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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#81
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
On Nov 23, 3:05*pm, Bob Engelhardt wrote:
wrote: ... * * * * *D1 * * * .--||--+-----+---- (+) to caliper * * + | * * * | * * | * .------. *+ | * * | * | * * *| * --- * --- * | ---- | * --- * \ / ~~ * | * * *| *C1| * *--- * | ---- | * *| * * | LED (red) * | * * *| * *| * * | * '------' * *| * * | * *- | PV * * | * * | * * *'--------+-----+--- (-) to caliper ... Doncha' need a current limiter on the LED? Bob Nope. These little PV panels barely manage 1 or 2 mA even in sunlight, 20uA under fluorescent. The LED's good for 10x the PV's max. output. I dragged an old calculator panel out[*] and connected it to one of those 0.6F super caps. It's charging the cap 1mV/8s, with no load. [*] this panel is 10x55mm--much larger than the one I referenced. I have several of the smaller ones, but they're all still working hard in $1 Walmart calculators. It's pretty impractical (clunky, delicate), but fun. -- Cheers, James Arthur |
#82
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
On Nov 23, 4:03*pm, Winston wrote:
wrote: (...) I saw a solar-powered Mitutoyo at a flea market and was intrigued, but resisted. Next time, advise jump on it before someone else does. I have two of those. They just keep working without any issues. *Well, except for turning off in low-light situations. *I just charge it up with the flashlight and it works just fine. *'Way better than having to run to the store for a $5 battery! *They are fine tools and have my highest recommendation. Yes, but I got one of the HF's and hacked it up with a Dremel tool, to mount to the lathe. Can't do that with a Mitutoyo! -- Cheers, James Arthur |
#83
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
John S wrote:
On 11/23/2011 2:05 PM, Bob Engelhardt wrote: Doncha' need a current limiter on the LED? Not if the PV cell's rated SC current is less than the max LED current rating. Isn't the capacitor's rated current MUCH more than the LED's? Bob |
#84
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
Winston wrote:
Bob Engelhardt wrote: Doncha' need a current limiter on the LED? Nup. It's a 'shunt regulator'. http://en.wikipedia.org/wiki/Linear_...ener_regulator The wiki ckt has a current-limiting resistor in series with the voltage source. Not so the posted ckt. Bob |
#85
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
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#86
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
Bob Engelhardt wrote:
Winston wrote: Bob Engelhardt wrote: Doncha' need a current limiter on the LED? Nup. It's a 'shunt regulator'. http://en.wikipedia.org/wiki/Linear_...ener_regulator The wiki ckt has a current-limiting resistor in series with the voltage source. Not so the posted ckt. It *is* in the posted circuit. Sort of. As James mentions, the internal resistance of the PV cell is the current-limiting resistor. --Winston --The BSA B50T POS used a single power zener across the battery as it's only voltage regulator. |
#87
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
Winston wrote:
Bob Engelhardt wrote: The wiki ckt has a current-limiting resistor in series with the voltage source. Not so the posted ckt. It *is* in the posted circuit. Sort of. As James mentions, the internal resistance of the PV cell is the current-limiting resistor. I meant the capacitor voltage source. Is its internal resistance a sufficient current limiter? I'm not familiar with super caps, but the common ones that I am familiar with will supply huge currents, momentarily. Bob |
#88
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
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#89
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
Bob Engelhardt wrote:
Winston wrote: Bob Engelhardt wrote: The wiki ckt has a current-limiting resistor in series with the voltage source. Not so the posted ckt. It *is* in the posted circuit. Sort of. As James mentions, the internal resistance of the PV cell is the current-limiting resistor. I meant the capacitor voltage source. Is its internal resistance a sufficient current limiter? I'm not familiar with super caps, but the common ones that I am familiar with will supply huge currents, momentarily. This circuit, yes? D1 .--||--+-----+---- (+) to caliper + | | | .------. + | | | | --- --- | ---- | --- \ / ~~ | | C1| --- | ---- | | | LED (red) | | | | '------' | | - | PV | | '--------+-----+--- (-) to caliper Under no circumstances would the voltage across the LED (and capacitor) go above, say 1.8 V because the LED turns any additional voltage into current. In order for C1 to produce a current large enough to endanger the LED or the caliper, it would have to be allowed to charge significantly above the 'zener point' of the LED. It just cannot. --Winston |
#90
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
On 11/23/2011 4:56 PM, Bob Engelhardt wrote:
John S wrote: On 11/23/2011 2:05 PM, Bob Engelhardt wrote: Doncha' need a current limiter on the LED? Not if the PV cell's rated SC current is less than the max LED current rating. Isn't the capacitor's rated current MUCH more than the LED's? Bob What has that to do with it? The voltage is clamped. What are you missing? |
#91
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
I get my LR44's and CR2032's he http://www.infinitelights.com/alkali...batteries.html
Orders $20 ship free. I use more CR2032's. |
#92
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
Winston wrote:
This circuit, yes? D1 .--||--+-----+---- (+) to caliper + | | | .------. + | | | | --- --- | ---- | --- \ / ~~ | | C1| --- | ---- | | | LED (red) | | | | '------' | | - | PV | | '--------+-----+--- (-) to caliper Under no circumstances would the voltage across the LED (and capacitor) go above, say 1.8 V because the LED turns any additional voltage into current. ... Oh ... right ... yeah. Dope slap for me. Bob |
#93
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
Bob Engelhardt wrote:
Winston wrote: This circuit, yes? (...) Under no circumstances would the voltage across the LED (and capacitor) go above, say 1.8 V because the LED turns any additional voltage into current. ... Oh ... right ... yeah. We are all here to learn. --Winston |
#95
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
On Nov 24, 5:20*pm, Jeff Liebermann wrote:
On Wed, 23 Nov 2011 06:45:46 -0800 (PST), wrote: The max. solar panel voltage doesn't matter--the LED regulator clamps the solar panel voltage, taking care of that. Yeah, but shunt regulators and leaky super-caps are not really appropriate for micropower devices. *They waste power. Small, cheap and simple are the main factors here. The r.c.m. guys aren't going to be building switching regulators, and switching regulators generally aren't more efficient at these power levels anyhow--their quiescent current draw's too high. (I've made a study of designing microwatt switchers, from scratch. It's possible, but wholly inappropriate here.) In a previous message, James Arthur measured: * Drain: 13.5uA (off), 14.5uA (on) * Battery low threshold (blinking display): 1.37V * Lowest operating voltage: 1.01V Nominal voltage on a silver oxide battery is 1.5V. *Therefore, the operating power is: * *1.5VDC * 15uA = 22.5 microwatts. From the standpoint of a resistive load, that's about: * *1.5VDC / 15 uA = 100K ohms The first question is whether a small solar cell will product 22.5 microwatts. *Testing a somewhat oversized polycrystaline cell that I found in my junk box (quality unknown), it produces 3.0VDC at 6ma with a short circuit load (my milliamps guesser). *My guess(tm) is that this cell is about three times as big as will conveniently fit on the calipers, so I'll just cut the current to 2ma . *Delivered power with my desk lamp is 6 milliwatts. *Yeah, it will a 22.5 microwatt load. Not so fast... The advantage of the thin-film PV panels is that (appropriate) panels excel at producing power even in dim light. Polycrystalline silicon panels don't. The array I suggested for experimentation is thin-film for that reason--so it can work in indoor light levels. The next question is for how long will it run? *Assuming the calipers can handle 3.0VDC without damage, how long will a junk 100UF electrolytic cap run the calipers? a) How long will it run? Not nearly long enough, and b) 3.0VDC is waayyy too risky for my blood. 20uA will discharge 100uF from 2.0V to 1.35V in 3.25 seconds. Of the setup I suggested, the most marginal part is the itty bitty PV panel (its output is on the low side). Dark leakage on my much-larger 10x55mm calculator panel is about 8uA @ 1.7V bias. The supercap works wonderfully well. Charge 0.6F to 1.8V, and you've got 4 hours' runtime until you reach the 1.35V battery-low display- starts-blinking level. (Assuming 20uA total draw, to allow for some leakage.) http://www.kpsec.freeuk.com/capacit.htm From 1.37V is roughly 50% of full 3.0VDC charge. *That's about 80% of 1RC time constant. *1RC is: * *0.8 * 100K * 1000uF = 80 seconds That's probably enough to make a few measurements. *Any longer and a super-cap will probably be needed. *Picking 50% of full charge out of the hat is rather convenient, as it makes the time to charge from zero to the dropout point the same 80 seconds (yes, I'm lazy). *Whether the user really wants to wait 1.5 minutes under a desk lamp for the calipers to be usable is dubious. *Of course, a longer run time, means a longer charge time. *For example, a 1F 5V 1ua leakage super-cap, will run the calipers for 80,000 seconds, but will also take 80,000 seconds to charge. Not 80,000s. Expose the PV to sunlight (or directly to a lamp), and it'll charge (initially) 50x faster. You'd only have to do that once. Indoors, the PV would keep it topped off, that's the idea. Alternatively, an electrolytic works, but gives a caliper that quickly quits if you accidentally shadow it. There are much smaller supercaps--0.02F--used in cellphones. That's another option / compromise. Leakage should be better too. There are low voltage DC-DC boost/buck switching regulator chips available that can tolerate a wide range of input voltages, and deliver a constant 1.5VDC. In my never humble opinion, what makes more sense is to do it exactly like the typical solar powered calculator. *They all have one or two LR44 batteries inside. *However, the solar cell does NOT charge the battery. *When you turn the calculator on, and there's enough light to run from the solar cell, the battery is essentially disconnected. When there's not enough light to run the calculator, it runs off the battery. *No waiting to charge a capacitor from the solar cell. That uses the PV as, basically, a battery-extender. That's fine, but complex--you need a micro-power switch to disconnect the battery, etc. (A diode drops waayyy too much voltage.) That puts it out of the realm of a simple project that can fit into the existing caliper. If you're into high tech, there are various energy scavenging devices that can also power the calipers. http://en.wikipedia.org/wiki/Energy_harvesting With only 22.5 microwatts required, it might be possible to power the device with a wind up key, piezo pressure, body heat, kinetic magnetic generator, etc. *I kinda like the idea of a wind up caliper. Windup would be fun--steampunk. The "real" solution is to design the caliper to draw less current in the first place, like Mitutoyo and Starrett. If you've done that, solar-powering is a snap, but then, if the battery lasts years, you don't need solar power, do you? -- Cheers, James Arthur |
#96
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
On 2011-11-23, Bob Engelhardt wrote:
Winston wrote: Bob Engelhardt wrote: The wiki ckt has a current-limiting resistor in series with the voltage source. Not so the posted ckt. It *is* in the posted circuit. Sort of. As James mentions, the internal resistance of the PV cell is the current-limiting resistor. I meant the capacitor voltage source. Is its internal resistance a sufficient current limiter? I'm not familiar with super caps, but the common ones that I am familiar with will supply huge currents, momentarily. The capacitor gets its voltage from the PV cell. Assuming that you don't put a switch between the LED and the cap (there is none shown in the schematic), the cap will never charge high enough to be able to damage the LED, because the LED will have already clamped the maximum voltage based on the current limit of the PV cell. Not sure what would happen with the PV cell close to an arc welding process like a TIG -- it depends on the internal resistance of the PV cell and the peak voltage which the PV cell can produce with such excessive illumination. Enjoy, DoN. -- Remove oil spill source from e-mail Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
#97
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
On Thu, 24 Nov 2011 18:13:15 -0800 (PST),
wrote: I found this, which calculates and measures caliper battery life: http://www.davehylands.com/Machinist/Caliper-Batteries/ Small, cheap and simple are the main factors here. The r.c.m. guys aren't going to be building switching regulators, and switching regulators generally aren't more efficient at these power levels anyhow--their quiescent current draw's too high. True. However, switching regulators usually have some manner of load shedding when the supply voltage is insufficient. Below that threshold, the current drain is usually in nanoamps. (I've made a study of designing microwatt switchers, from scratch. It's possible, but wholly inappropriate here.) You're ahead of me. I've never designed anything in that low power class. Different world. Can you point me to a suitable (or close to suitable) regulator chip? Not so fast... The advantage of the thin-film PV panels is that (appropriate) panels excel at producing power even in dim light. Polycrystalline silicon panels don't. The array I suggested for experimentation is thin-film for that reason--so it can work in indoor light levels. Decisions, decisions, and more decisions. Polycrystaline has a cost advantage and is more efficient than single layer thin-film. Well, if I wanted to go cheap, I would use amorphous cells and mold them into the plastic case. For small solar cells, the cost of monocrystaline isn't all that much more (i.e. most of the cost is in packaging and handling) but won't work well with indoor lighting. So, I guess thin-film is the least disgusting. http://en.wikipedia.org/wiki/Solar_powered_calculator "Solar calculators may not work well in indoor conditions under ambient lighting as sufficient lighting is not available." The next question is for how long will it run? *Assuming the calipers can handle 3.0VDC without damage, how long will a junk 100UF electrolytic cap run the calipers? a) How long will it run? Not nearly long enough, and b) 3.0VDC is waayyy too risky for my blood. 20uA will discharge 100uF from 2.0V to 1.35V in 3.25 seconds. I used 1000uF elsewhere in my calcs, but slipped here and used 100uF instead. Sorry. I think you might be a bit too conservative. 5ua leakage is high. Most of the spec sheets I've skimmed show 1-2ua for a typical 1F 5.5V super-cap. Of the setup I suggested, the most marginal part is the itty bitty PV panel (its output is on the low side). Dark leakage on my much-larger 10x55mm calculator panel is about 8uA @ 1.7V bias. The alternative is to lose approximately 0.3V in a series Schottky diode. That's about 20% of the power budget, which is probably too much. The supercap works wonderfully well. Charge 0.6F to 1.8V, and you've got 4 hours' runtime until you reach the 1.35V battery-low display- starts-blinking level. (Assuming 20uA total draw, to allow for some leakage.) Ok. You've sold me. I was trying to see what could be done with commodity electrolytic caps. Also, super-caps fail to appreciate high humidity, which may become a problem. http://www.kpsec.freeuk.com/capacit.htm From 1.37V is roughly 50% of full 3.0VDC charge. *That's about 80% of 1RC time constant. *1RC is: * *0.8 * 100K * 1000uF = 80 seconds That's probably enough to make a few measurements. *Any longer and a super-cap will probably be needed. *Picking 50% of full charge out of the hat is rather convenient, as it makes the time to charge from zero to the dropout point the same 80 seconds (yes, I'm lazy). *Whether the user really wants to wait 1.5 minutes under a desk lamp for the calipers to be usable is dubious. *Of course, a longer run time, means a longer charge time. *For example, a 1F 5V 1ua leakage super-cap, will run the calipers for 80,000 seconds, but will also take 80,000 seconds to charge. Not 80,000s. Expose the PV to sunlight (or directly to a lamp), and it'll charge (initially) 50x faster. You'd only have to do that once. Indoors, the PV would keep it topped off, that's the idea. Yep. However, I screwed up. The discharge load is: 1.5VDC / 15uA = 100K ohms However, the charging ESR is much less. 3.0VDC / 2ma = 1.5K It will certainly be higher a lower illumination levels. Checking my junk cell under random room lighting conditions, and again scaling for size, I get: 0.333 * 0.55v / 0.02mA = 9.2K I don't have a small thin film panel to test. (I have 90watt panel, but that's a bit much for scaling to caliper size). Alternatively, an electrolytic works, but gives a caliper that quickly quits if you accidentally shadow it. Not if you do exactly like it's done with a calculator. When the cell is shaded, it runs on battery. A silver-oxide battery holds: 1.5v * 150 mA-Hr = 22.5 milliwatt-Hrs and will deliver most of that before the voltage drops to unusable levels. The super cap will deliver (very roughly): 1.5v * 15uA * 4Hr = 90 microwatt-Hrs There are much smaller supercaps--0.02F--used in cellphones. That's another option / compromise. Leakage should be better too. Overview of CDE super-caps: http://www.cde.com/catalogs/EDL.pdf Some interesting notes on charge time and lifetime near the bottom. In my never humble opinion, what makes more sense is to do it exactly like the typical solar powered calculator. *They all have one or two LR44 batteries inside. *However, the solar cell does NOT charge the battery. *When you turn the calculator on, and there's enough light to run from the solar cell, the battery is essentially disconnected. When there's not enough light to run the calculator, it runs off the battery. *No waiting to charge a capacitor from the solar cell. That uses the PV as, basically, a battery-extender. That's fine, but complex--you need a micro-power switch to disconnect the battery, etc. (A diode drops waayyy too much voltage.) That puts it out of the realm of a simple project that can fit into the existing caliper. There has to be a chip in the calipers anyway to count pulses, run the display, and deal with the push buttons. Adding a power management feature does not add much real estate or complexity. However, if you're thinking of a retrofit, I suspect something could be done with a separate switcher chip. If you're into high tech, there are various energy scavenging devices that can also power the calipers. http://en.wikipedia.org/wiki/Energy_harvesting With only 22.5 microwatts required, it might be possible to power the device with a wind up key, piezo pressure, body heat, kinetic magnetic generator, etc. *I kinda like the idea of a wind up caliper. Windup would be fun--steampunk. In the late 1960's, I designed and built a paging receiver, that produced the message output on a 1/4" wide roll of paper tape. Battery power to the mechanics for such a portable device was impossible. So, I went to a wind up coil spring mechanism. I've been somewhat of a fan of spring power ever since. The "real" solution is to design the caliper to draw less current in the first place, like Mitutoyo and Starrett. If you've done that, solar-powering is a snap, but then, if the battery lasts years, you don't need solar power, do you? Agreed. It would be like a digital watch, which typically has a 10 year battery life. However, the solar cell is still a problem because of the dark current (reverse leakage). An isolating Schottky diode can reduce that, but then the solar cell would need to be about 20% larger to compensate for the added loss. Another problem is that it would be no fun. Windup calipers offer a far more entertaining problem to solve. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#98
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
On Thu, 24 Nov 2011 21:46:48 -0800, Jeff Liebermann
wrote: The next question is for how long will it run? *Assuming the calipers can handle 3.0VDC without damage, how long will a junk 100UF electrolytic cap run the calipers? a) How long will it run? Not nearly long enough, and b) 3.0VDC is waayyy too risky for my blood. 20uA will discharge 100uF from 2.0V to 1.35V in 3.25 seconds. Trying the same calc using the super-cap formula from Pg 6 of: http://www.cde.com/catalogs/EDL.pdf t = C delta V / I t = C[V0-(i*R)-V1] / (i+iL) whe t: Back-up time (sec) C: Capacitance of Type EDL (Farads) V0: Applied voltage (Volts) V1: Cut-off voltage (Volts) i: Current during back-up (Amps) iL: Leakage current (Amps) R: Internal resistance (ohms) at 1 kHz For this example, I'll use a 0.1F (type F) 5.5V 100 ohm cap. The low end of the tolerance range might drop this to 0.08F. V0 = 2.0V, V1 = 1.4V, i = 15uA, iL = 2uA Plugging in: t = C[V0-(i*R)-V1] / (i+iL) t = 0.08F[2.0V-(15uA*100ohms)-1.4V]/(15uA+2uA) t = 2800 sec = 47 minutes. Not bad. I guess the protective case that most calipers use will need a clear plastic window to keep it charged. Maybe another window on top of my toolbox. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#99
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
On Thu, 24 Nov 2011 22:29:50 -0800, Jeff Liebermann
wrote: On Thu, 24 Nov 2011 21:46:48 -0800, Jeff Liebermann wrote: The next question is for how long will it run? *Assuming the calipers can handle 3.0VDC without damage, how long will a junk 100UF electrolytic cap run the calipers? a) How long will it run? Not nearly long enough, and b) 3.0VDC is waayyy too risky for my blood. 20uA will discharge 100uF from 2.0V to 1.35V in 3.25 seconds. Trying the same calc using the super-cap formula from Pg 6 of: http://www.cde.com/catalogs/EDL.pdf t = C delta V / I t = C[V0-(i*R)-V1] / (i+iL) whe t: Back-up time (sec) C: Capacitance of Type EDL (Farads) V0: Applied voltage (Volts) V1: Cut-off voltage (Volts) i: Current during back-up (Amps) iL: Leakage current (Amps) R: Internal resistance (ohms) at 1 kHz For this example, I'll use a 0.1F (type F) 5.5V 100 ohm cap. The low end of the tolerance range might drop this to 0.08F. V0 = 2.0V, V1 = 1.4V, i = 15uA, iL = 2uA Plugging in: t = C[V0-(i*R)-V1] / (i+iL) t = 0.08F[2.0V-(15uA*100ohms)-1.4V]/(15uA+2uA) t = 2800 sec = 47 minutes. Not bad. I guess the protective case that most calipers use will need a clear plastic window to keep it charged. Maybe another window on top of my toolbox. http://www.judgetool.com/500seriessu...weredip67.aspx http://www.widgetsupply.com/page/WS/...-digital/BAP30 (only 2 digits) http://www.alibaba.com/showroom/sola...l-caliper.html Quite a number of them..... One could not be a successful Leftwinger without realizing that, in contrast to the popular conception supported by newspapers and mothers of Leftwingers, a goodly number of Leftwingers are not only narrow-minded and dull, but also just stupid. Gunner Asch |
#100
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
On Nov 25, 12:46*am, Jeff Liebermann wrote:
On Thu, 24 Nov 2011 18:13:15 -0800 (PST), wrote: I found this, which calculates and measures caliper battery life: http://www.davehylands.com/Machinist/Caliper-Batteries/ Yes, good site. I linked to it earlier in this thread. Small, cheap and simple are the main factors here. *The r.c.m. guys aren't going to be building switching regulators, and switching regulators generally aren't more efficient at these power levels anyhow--their quiescent current draw's too high. True. *However, switching regulators usually have some manner of load shedding when the supply voltage is insufficient. *Below that threshold, the current drain is usually in nanoamps. (I've made a study of designing microwatt switchers, from scratch. It's possible, but wholly inappropriate here.) You're ahead of me. *I've never designed anything in that low power class. *Different world. *Can you point me to a suitable (or close to suitable) regulator chip? There aren't any ICs with low enough Iq, at least not that I know of. I used discrete transistors. Not so fast... *The advantage of the thin-film PV panels is that (appropriate) panels excel at producing power even in dim light. Polycrystalline silicon panels don't. The array I suggested for experimentation is thin-film for that reason--so it can work in indoor light levels. Decisions, decisions, and more decisions. *Polycrystaline has a cost advantage and is more efficient than single layer thin-film. *Well, if I wanted to go cheap, I would use amorphous cells and mold them into the plastic case. *For small solar cells, the cost of monocrystaline isn't all that much more (i.e. most of the cost is in packaging and handling) but won't work well with indoor lighting. *So, I guess thin-film is the least disgusting. http://en.wikipedia.org/wiki/Solar_powered_calculator * *"Solar calculators may not work well in indoor * *conditions under ambient lighting as sufficient lighting * *is not available." You can scavenge a PV from a cheap solar calculator, as low as $1. I also linked to a part from Goldmine-elec.com. Polycrystalline cells put out lots more in bright light, but AFAIK, all solar calculators (and calipers, for that matter), use the amorphous (thin-film) cells for the low-light performance. Cost might also be a factor. The next question is for how long will it run? *Assuming the calipers can handle 3.0VDC without damage, how long will a junk 100UF electrolytic cap run the calipers? a) How long will it run? *Not nearly long enough, and b) 3.0VDC is waayyy too risky for my blood. *20uA will discharge 100uF from 2.0V to 1.35V in 3.25 seconds. I used 1000uF elsewhere in my calcs, but slipped here and used 100uF instead. *Sorry. I think you might be a bit too conservative. *5ua leakage is high. Most of the spec sheets I've skimmed show 1-2ua for a typical 1F 5.5V super-cap. Of the setup I suggested, the most marginal part is the itty bitty PV panel (its output is on the low side). *Dark leakage on my much-larger 10x55mm calculator panel is about 8uA @ 1.7V bias. The alternative is to lose approximately 0.3V in a series Schottky diode. *That's about 20% of the power budget, which is probably too much. I believe the panels put out a high enough overvoltage that the diode loss doesn't matter--it's only going to get wasted in the LED shunt regulators any how. I'll check. MEASUREMENTS Panel: 4-section 10x50mm panel, from a (retired) TI calculator: Lighting 1: 1.8V (open), 18.5uA (short-circuit) Lighting 2: 2.5V (open), 300uA (short-circuit) [1] Modest indoor light (indirect sunlight, filtering through blinds, measured from the ceiling bounce). [2] 2' from 20W halogen bulb. So, a 1n4148 drops too much for comfort. A BAT54 drops about 150mV forward at these currents, and leaks a fraction of a uA at these temperatures and reverse biases. Or, you could omit the diode and just let the thing power down in the shade. The supercap works wonderfully well. *Charge 0.6F to 1.8V, and you've got 4 hours' runtime until you reach the 1.35V battery-low display- starts-blinking level. (Assuming 20uA total draw, to allow for some leakage.) Ok. *You've sold me. *I was trying to see what could be done with commodity electrolytic caps. *Also, super-caps fail to appreciate high humidity, which may become a problem. http://www.kpsec.freeuk.com/capacit.htm From 1.37V is roughly 50% of full 3.0VDC charge. *That's about 80% of 1RC time constant. *1RC is: * *0.8 * 100K * 1000uF = 80 seconds That's probably enough to make a few measurements. *Any longer and a super-cap will probably be needed. *Picking 50% of full charge out of the hat is rather convenient, as it makes the time to charge from zero to the dropout point the same 80 seconds (yes, I'm lazy). *Whether the user really wants to wait 1.5 minutes under a desk lamp for the calipers to be usable is dubious. *Of course, a longer run time, means a longer charge time. *For example, a 1F 5V 1ua leakage super-cap, will run the calipers for 80,000 seconds, but will also take 80,000 seconds to charge. Not 80,000s. *Expose the PV to sunlight (or directly to a lamp), and it'll charge (initially) 50x faster. *You'd only have to do that once. *Indoors, the PV would keep it topped off, that's the idea. Yep. *However, I screwed up. *The discharge load is: * *1.5VDC / 15uA = 100K ohms However, the charging ESR is much less. * *3.0VDC / 2ma = 1.5K It will certainly be higher a lower illumination levels. *Checking my junk cell under random room lighting conditions, and again scaling for size, I get: * *0.333 * 0.55v / 0.02mA = 9.2K I don't have a small thin film panel to test. *(I have 90watt panel, but that's a bit much for scaling to caliper size). Alternatively, an electrolytic works, but gives a caliper that quickly quits if you accidentally shadow it. Not if you do exactly like it's done with a calculator. *When the cell is shaded, it runs on battery. *A silver-oxide battery holds: * *1.5v * 150 mA-Hr = 22.5 milliwatt-Hrs and will deliver most of that before the voltage drops to unusable levels. The super cap will deliver (very roughly): * *1.5v * 15uA * 4Hr = 90 microwatt-Hrs There are much smaller supercaps--0.02F--used in cellphones. *That's another option / compromise. *Leakage should be better too. Overview of CDE super-caps: http://www.cde.com/catalogs/EDL.pdf Some interesting notes on charge time and lifetime near the bottom. In my never humble opinion, what makes more sense is to do it exactly like the typical solar powered calculator. *They all have one or two LR44 batteries inside. *However, the solar cell does NOT charge the battery. *When you turn the calculator on, and there's enough light to run from the solar cell, the battery is essentially disconnected. When there's not enough light to run the calculator, it runs off the battery. *No waiting to charge a capacitor from the solar cell. That uses the PV as, basically, a battery-extender. *That's fine, but complex--you need a micro-power switch to disconnect the battery, etc. (A diode drops waayyy too much voltage.) *That puts it out of the realm of a simple project that can fit into the existing caliper. There has to be a chip in the calipers anyway to count pulses, run the display, and deal with the push buttons. *Adding a power management feature does not add much real estate or complexity. *However, if you're thinking of a retrofit, I suspect something could be done with a separate switcher chip. If we're designing it from scratch, we just wouldn't use so darn much power to start with. Then, a PV panel and a capacitor are all you need. Switcher chips just don't do well on 20uA power input. If you're into high tech, there are various energy scavenging devices that can also power the calipers. http://en.wikipedia.org/wiki/Energy_harvesting With only 22.5 microwatts required, it might be possible to power the device with a wind up key, piezo pressure, body heat, kinetic magnetic generator, etc. *I kinda like the idea of a wind up caliper. Windup would be fun--steampunk. In the late 1960's, I designed and built a paging receiver, that produced the message output on a 1/4" wide roll of paper tape. Battery power to the mechanics for such a portable device was impossible. *So, I went to a wind up coil spring mechanism. *I've been somewhat of a fan of spring power ever since. The "real" solution is to design the caliper to draw less current in the first place, like Mitutoyo and Starrett. *If you've done that, solar-powering is a snap, but then, if the battery lasts years, you don't need solar power, do you? Agreed. *It would be like a digital watch, which typically has a 10 year battery life. *However, the solar cell is still a problem because of the dark current (reverse leakage). *An isolating Schottky diode can reduce that, but then the solar cell would need to be about 20% larger to compensate for the added loss. Another problem is that it would be no fun. *Windup calipers offer a far more entertaining problem to solve. Windup calipers--that's cool! -- Cheers, James Arthur |
#101
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
On Nov 25, 1:29*am, Jeff Liebermann wrote:
On Thu, 24 Nov 2011 21:46:48 -0800, Jeff Liebermann wrote: The next question is for how long will it run? *Assuming the calipers can handle 3.0VDC without damage, how long will a junk 100UF electrolytic cap run the calipers? a) How long will it run? *Not nearly long enough, and b) 3.0VDC is waayyy too risky for my blood. *20uA will discharge 100uF from 2.0V to 1.35V in 3.25 seconds. Trying the same calc using the super-cap formula from Pg 6 of: http://www.cde.com/catalogs/EDL.pdf * *t = C delta V / I * *t = C[V0-(i*R)-V1] / (i+iL) whe * * t: Back-up time (sec) * * C: Capacitance of Type EDL (Farads) * *V0: Applied voltage (Volts) * *V1: Cut-off voltage (Volts) * * i: Current during back-up (Amps) * *iL: Leakage current (Amps) * * R: Internal resistance (ohms) at 1 kHz For this example, I'll use a 0.1F (type F) 5.5V 100 ohm cap. The low end of the tolerance range might drop this to 0.08F. V0 = 2.0V, V1 = 1.4V, i = 15uA, iL = 2uA That cap is 14x10mm, pretty humungous. You don't need 5.5v, so the 'EN' type, at 7x2mm and 0.2F might be a better fit. Plugging in: *t = C[V0-(i*R)-V1] / (i+iL) *t = 0.08F[2.0V-(15uA*100ohms)-1.4V]/(15uA+2uA) *t = 2800 sec = 47 minutes. Not bad. I calculated the caliper as being a constant-current drain on the super cap, then applied Q=CV. Actual current drain drops a tad with falling Vdd, so my approximation is probably slightly conservative. I guess the protective case that most calipers use will need a clear plastic window to keep it charged. *Maybe another window on top of my toolbox. Yep. Another retro-fit possibility is to fit a supercap in the caliper, and a lithium-AA (1.65v) in the caliper case that recharges the supercap when not in use. That'll last forever (about 10years on the 'AA'), runs for hours per charge, fits the case easily, and doesn't need a PV or any fancy circuitry. The PAS920 I linked before costs 5/$1 surplus, from Goldmine-elec.com. -- Cheers, James Arthur |
#102
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
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#103
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
On Nov 25, 5:31*pm, "
wrote: On Fri, 25 Nov 2011 07:06:57 -0800 (PST), wrote: On Nov 25, 12:46*am, Jeff Liebermann wrote: On Thu, 24 Nov 2011 18:13:15 -0800 (PST), wrote: I found this, which calculates and measures caliper battery life: http://www.davehylands.com/Machinist/Caliper-Batteries/ Yes, good site. *I linked to it earlier in this thread. Small, cheap and simple are the main factors here. *The r.c.m. guys aren't going to be building switching regulators, and switching regulators generally aren't more efficient at these power levels anyhow--their quiescent current draw's too high. True. *However, switching regulators usually have some manner of load shedding when the supply voltage is insufficient. *Below that threshold, the current drain is usually in nanoamps. (I've made a study of designing microwatt switchers, from scratch. It's possible, but wholly inappropriate here.) You're ahead of me. *I've never designed anything in that low power class. *Different world. *Can you point me to a suitable (or close to suitable) regulator chip? There aren't any ICs with low enough Iq, at least not that I know of. I used discrete transistors. There are some pretty good ones, designed for USB applications, but I don't thing they're quite good enough for this. The TPS6205x Iq is around 5uA to and in shutdown less than 2uA. *You're looking for something an order of magnitude better than this? ... http://www.ti.com/lit/ds/symlink/tps62050.pdf From the graph on the front page, it looks like n = ~35% @ 15uA output. That's actually very good. Thanks. My designs were mostly boost topology, so there may be ICs I didn't consider (plus new ICs I haven't seen). I did some nutty stuff, like nano-amp oscillators and micro-amp switchers that were roughly 75% efficient. -- Cheers, James Arthur |
#104
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
On Fri, 25 Nov 2011 21:28:54 -0800 (PST),
wrote: On Nov 25, 5:31*pm, " wrote: (...) http://www.ti.com/lit/ds/symlink/tps62050.pdf From the graph on the front page, it looks like n = ~35% @ 15uA output. That's actually very good. Thanks. That's because of the 12uA typical quiescent current, where the chip draws about the same current as the caliper load. For equal currents, that's 50% maximum efficiency. The TPS62054 shows 50% efficiency at 2.7V in and 1.8V out (See Pg 8 Fig 4). The chips do have a shutdown pin that cuts the quiescent current to "less than 2uA". Still high, but much better. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#105
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
"Jeff Liebermann" wrote in message
... That's because of the 12uA typical quiescent current, where the chip draws about the same current as the caliper load. For equal currents, that's 50% maximum efficiency. The TPS62054 shows 50% efficiency at 2.7V in and 1.8V out (See Pg 8 Fig 4). The chips do have a shutdown pin that cuts the quiescent current to "less than 2uA". Still high, but much better. A step-down regulator/converter could be made from a Microchip PIC18LF14K22 (http://ww1.microchip.com/downloads/e...Doc/41365c.pdf) which has a quiescent current of 34nA and an operating current of about 10 uA at 1.8 VDC. And it may be even more efficient to use a low power linear regulator such as the TPS71501 (http://www.ti.com/product/tps71501) which has 3.3 uA quiescent current. If the input voltage is, say, 2 VDC and the output is 1.6 VDC at 12 uA, the overall efficiency is (1.6*12)/(2*15.3) or almost 63%. Even at 3 VDC input it is 42%. Paul |
#106
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
On Nov 26, 12:36*pm, Jeff Liebermann wrote:
On Fri, 25 Nov 2011 21:28:54 -0800 (PST), wrote: On Nov 25, 5:31*pm, " wrote: (...) http://www.ti.com/lit/ds/symlink/tps62050.pdf From the graph on the front page, it looks like n = ~35% *@ 15uA output. *That's actually very good. *Thanks. That's because of the 12uA typical quiescent current, where the chip draws about the same current as the caliper load. *For equal currents, that's 50% maximum efficiency. *The TPS62054 shows 50% efficiency at 2.7V in and 1.8V out (See Pg 8 Fig 4). The chips do have a shutdown pin that cuts the quiescent current to "less than 2uA". *Still high, but much better. Yes, but, in the caliper context, who's going to turn the switcher off, how, and when? See the problem? -- Cheers, James Arthur |
#107
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
On Nov 26, 5:09*pm, "P E Schoen" wrote:
"Jeff Liebermann" *wrote in message ... That's because of the 12uA typical quiescent current, where the chip draws about the same current as the caliper load. *For equal currents, that's 50% maximum efficiency. *The TPS62054 shows 50% efficiency at 2.7V in and 1.8V out (See Pg 8 Fig 4). The chips do have a shutdown pin that cuts the quiescent current to "less than 2uA". *Still high, but much better. A step-down regulator/converter could be made from a Microchip PIC18LF14K22 (http://ww1.microchip.com/downloads/e...Doc/41365c.pdf) which has a quiescent current of 34nA and an operating current of about 10 uA at 1.8 VDC. And it may be even more efficient to use a low power linear regulator such as the TPS71501 (http://www.ti.com/product/tps71501) which has 3.3 uA quiescent current. If the input voltage is, say, 2 VDC and the output is 1.6 VDC at 12 uA, the overall efficiency is (1.6*12)/(2*15.3) or almost 63%. Even at 3 VDC input it is 42%. Paul The LED shunt regulator saves the 2uA, so it's simpler, cheaper, and even more efficient. -- Cheers, James Arthur |
#108
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
On Sun, 27 Nov 2011 07:35:00 -0800 (PST), wrote:
On Nov 26, 12:36*pm, Jeff Liebermann wrote: On Fri, 25 Nov 2011 21:28:54 -0800 (PST), wrote: On Nov 25, 5:31*pm, " wrote: (...) http://www.ti.com/lit/ds/symlink/tps62050.pdf From the graph on the front page, it looks like n = ~35% *@ 15uA output. *That's actually very good. *Thanks. That's because of the 12uA typical quiescent current, where the chip draws about the same current as the caliper load. *For equal currents, that's 50% maximum efficiency. *The TPS62054 shows 50% efficiency at 2.7V in and 1.8V out (See Pg 8 Fig 4). The chips do have a shutdown pin that cuts the quiescent current to "less than 2uA". *Still high, but much better. Yes, but, in the caliper context, who's going to turn the switcher off, how, and when? When the photocell voltage output too low to power the calipers? See the problem? |
#109
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
On Sun, 27 Nov 2011 07:35:00 -0800 (PST),
wrote: On Nov 26, 12:36*pm, Jeff Liebermann wrote: On Fri, 25 Nov 2011 21:28:54 -0800 (PST), wrote: On Nov 25, 5:31*pm, " wrote: (...) http://www.ti.com/lit/ds/symlink/tps62050.pdf From the graph on the front page, it looks like n = ~35% *@ 15uA output. *That's actually very good. *Thanks. That's because of the 12uA typical quiescent current, where the chip draws about the same current as the caliper load. *For equal currents, that's 50% maximum efficiency. *The TPS62054 shows 50% efficiency at 2.7V in and 1.8V out (See Pg 8 Fig 4). The chips do have a shutdown pin that cuts the quiescent current to "less than 2uA". *Still high, but much better. Yes, but, in the caliper context, who's going to turn the switcher off, how, and when? A timer. Caliper runs for 120 seconds and then shuts off. I have a few small battery operated devices like this that have no OFF switch. Just punch any button, and it turns on. Wait a while, and it turns off. My Central Tools "Storm" 3C301 cheapo electronic calipers has this feature. http://www.amazon.com/Storm-6in-Digital-Caliper-Model/dp/B000VZ2ZB6 The unintelligible owners manual proudly highlights this feature on the cover. Apparently, previous versions did NOT turn off automatically. Oddly, it still has an on/off push button, even though it will turn on if the jaws are moved. Hmmm... the catalog says that it ships with an SR44/357 silver oxide battery. Yet, the one I purchased had alkaline LR44 batteries. http://www.centraltools.com/pdf/Catalog_Storm.pdf See the problem? Nope. I still think that wind up power would be more interesting. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#110
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
On Nov 27, 12:17*pm, Jeff Liebermann wrote:
On Sun, 27 Nov 2011 07:35:00 -0800 (PST), wrote: On Nov 26, 12:36*pm, Jeff Liebermann wrote: On Fri, 25 Nov 2011 21:28:54 -0800 (PST), wrote: On Nov 25, 5:31*pm, " wrote: (...) http://www.ti.com/lit/ds/symlink/tps62050.pdf From the graph on the front page, it looks like n = ~35% *@ 15uA output. *That's actually very good. *Thanks. That's because of the 12uA typical quiescent current, where the chip draws about the same current as the caliper load. *For equal currents, that's 50% maximum efficiency. *The TPS62054 shows 50% efficiency at 2.7V in and 1.8V out (See Pg 8 Fig 4). The chips do have a shutdown pin that cuts the quiescent current to "less than 2uA". *Still high, but much better. Yes, but, in the caliper context, who's going to turn the switcher off, how, and when? A timer. *Caliper runs for 120 seconds and then shuts off. But then the caliper forgets its "zero" every two minutes. That's very annoying. I have a few small battery operated devices like this that have no OFF switch. Just punch any button, and it turns on. *Wait a while, and it turns off. *My Central Tools "Storm" 3C301 cheapo electronic calipers has this feature. http://www.amazon.com/Storm-6in-Digital-Caliper-Model/dp/B000VZ2ZB6 The unintelligible owners manual proudly highlights this feature on the cover. *Apparently, previous versions did NOT turn off automatically. *Oddly, it still has an on/off push button, even though it will turn on if the jaws are moved. Hmmm... the catalog says that it ships with an SR44/357 silver oxide battery. *Yet, the one I purchased had alkaline LR44 batteries. http://www.centraltools.com/pdf/Catalog_Storm.pdf See the problem? Nope. The problem is that it's a much more complicated design, much more than a metalworking hobbyist could reasonably tackle to upgrade his HF cheapies. If we're designing calipers from scratch, we'd just design them for 2uA total draw, not add an outboard switcher with Iq=2uA, then add a timer to turn it off. I still think that wind up power would be more interesting. Yep, that's still intriguing. As a practical matter, how do you turn spring tension into 15uA / 1.55V? A generator, an escapement, a coil and a magnet I suppose. Time to call a watchmaker. -- Cheers, James Arthur |
#111
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
On Sun, 27 Nov 2011 10:45:00 -0800 (PST),
wrote: But then the caliper forgets its "zero" every two minutes. That's very annoying. Mine doesn't. The initial position is apparently stored in the circuitry. I can also set it to any position, turn it off, and it will read the same value when turned back on. One of the benefits of having it draw power continuously. The problem is that it's a much more complicated design, much more than a metalworking hobbyist could reasonably tackle to upgrade his HF cheapies. Retrofits are always more complicated. I tend to think in terms of new product designs. If this were for a retrofit or modification, the design philosphy would certainly be different. If we're designing calipers from scratch, we'd just design them for 2uA total draw, not add an outboard switcher with Iq=2uA, then add a timer to turn it off. Agreed. At 2uA, it probably wouldn't need an on/off switch. I still think that wind up power would be more interesting. Yep, that's still intriguing. As a practical matter, how do you turn spring tension into 15uA / 1.55V? A generator, an escapement, a coil and a magnet I suppose. Time to call a watchmaker. Pancake PM generator which offers the highest velocity at the edge. Basically a magnetized disk and a stator coil. Spring loaded spool parallel to the pancake motor and the same size. Ratchet to control direction. Inertial clutch and some plastic gears between the spool and the pancake motor. Much like a generator powered flashlight. Pull on the string and the spool spins, which causes the generator to run, charging a super-cap. If a pull string is too crude, a spiral mainspring mechanism can be added. If the pull string and generator are too sophisticated, a moving magnet inside a coil, that you shake back and forth to charge the super-cap, much like in some battery-less flashlights. Maybe a thumb wheel for spinning the pancake generator might better. Plenty of options. I can grind the energy budget numbers (later) if you want. There's plenty of power available in string pull and wind up. However, without a backup battery, the stored zero setting will be lost when the super-cap discharges. Such is the price of entertainment value. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#112
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
Jeff Liebermann wrote:
On Sun, 27 Nov 2011 10:45:00 -0800 (PST), wrote: But then the caliper forgets its "zero" every two minutes. That's very annoying. Mine doesn't. The initial position is apparently stored in the circuitry. I can also set it to any position, turn it off, and it will read the same value when turned back on. One of the benefits of having it draw power continuously. The problem is that it's a much more complicated design, much more than a metalworking hobbyist could reasonably tackle to upgrade his HF cheapies. Retrofits are always more complicated. I tend to think in terms of new product designs. If this were for a retrofit or modification, the design philosphy would certainly be different. If we're designing calipers from scratch, we'd just design them for 2uA total draw, not add an outboard switcher with Iq=2uA, then add a timer to turn it off. Agreed. At 2uA, it probably wouldn't need an on/off switch. I still think that wind up power would be more interesting. Yep, that's still intriguing. As a practical matter, how do you turn spring tension into 15uA / 1.55V? A generator, an escapement, a coil and a magnet I suppose. Time to call a watchmaker. Pancake PM generator which offers the highest velocity at the edge. Basically a magnetized disk and a stator coil. Spring loaded spool parallel to the pancake motor and the same size. Ratchet to control direction. Inertial clutch and some plastic gears between the spool and the pancake motor. Much like a generator powered flashlight. Pull on the string and the spool spins, which causes the generator to run, charging a super-cap. If a pull string is too crude, a spiral mainspring mechanism can be added. If the pull string and generator are too sophisticated, a moving magnet inside a coil, that you shake back and forth to charge the super-cap, much like in some battery-less flashlights. Maybe a thumb wheel for spinning the pancake generator might better. Plenty of options. How about a weighted leaf switch in series with the cell? It could take the form of a thicker 'battery door'. The bulk bypass caps in the caliper would hopefully maintain power during vibration glitches and overhead measurements. Place the caliper 'display down' and power is removed. --Winston--Cheap! Quick! |
#113
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
On Sun, 27 Nov 2011 14:08:41 -0800, Winston
wrote: How about a weighted leaf switch in series with the cell? It could take the form of a thicker 'battery door'. The bulk bypass caps in the caliper would hopefully maintain power during vibration glitches and overhead measurements. Place the caliper 'display down' and power is removed. --Winston--Cheap! Quick! Retch. A position sensitive on/off mechanism is prone to failure if the device is parked in an unusual position. For example, if I put it in it's protective case, and then toss it into my toolbox face up, it will remain on. It would also prevent me from using in the face down position. Please don't suggest an inertial on/off mechanism (shake to operate). Bouncing around in my car will probably turn it on. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#114
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
Jeff Liebermann wrote:
(...) Retch. A position sensitive on/off mechanism is prone to failure if the device is parked in an unusual position. For example, if I put it in it's protective case, and then toss it into my toolbox face up, it will remain on. Even if you stored the caliper 'face up' for a year, it would cost you no more than if you had no switch at all. Net net, battery life would increase because, the caliper would be turned off for a far longer time than it would be turned on. It would also prevent me from using in the face down position. I was appalled that I can't use my blender upside down too, until I realized that I never have a need to do that. Please don't suggest an inertial on/off mechanism (shake to operate). Bouncing around in my car will probably turn it on. If you drive your car 24/365, you have much bigger efficiency worries than a $1.00 cell! --Winston |
#115
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
On Sun, 27 Nov 2011 22:18:49 -0800, Winston
wrote: Jeff Liebermann wrote: (...) Retch. A position sensitive on/off mechanism is prone to failure if the device is parked in an unusual position. For example, if I put it in it's protective case, and then toss it into my toolbox face up, it will remain on. Even if you stored the caliper 'face up' for a year, it would cost you no more than if you had no switch at all. Net net, battery life would increase because, the caliper would be turned off for a far longer time than it would be turned on. This is what happens when we lose sight of the original problem that we're trying to solve. The problem is that the calipers have a short battery life mostly because they don't really turn off and secondarily because the dropout voltage is too high to use cheap alkaline batteries. Turning the calipers off (actually in standby) for a year won't do much, when the operating current is 14.5uA and the off current is 13.5uA. It would also prevent me from using in the face down position. I was appalled that I can't use my blender upside down too, until I realized that I never have a need to do that. You need to contact a product liability attorney, and sue for damages resulting from inverted operation. Be sure to mention that there was no warning in the user manual about inverted operation. I've used calipers and other measuring instruments in probably every orientation possible. If the calipers turned off while I was making measurements in a contortionists position, I would be rather irritated. Please don't suggest an inertial on/off mechanism (shake to operate). Bouncing around in my car will probably turn it on. If you drive your car 24/365, you have much bigger efficiency worries than a $1.00 cell! True. Also, if I don't drive the car at all, I get an infinitely large gasoline mileage. Both extremes are worthless. I non-cleverly installed a "shake to unlock" (iShakeLock) application on my iPhone 3G. The standard method of unlocking the phone requires both hands. I figured that one handed unlocking would be better. The problem was that it kept unlocking in my pocket. Battery life deteriorated rapidly. So, I dumped the app. -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
#116
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
Jeff Liebermann wrote:
On Sun, 27 Nov 2011 22:18:49 -0800, wrote: Jeff Liebermann wrote: (...) Retch. A position sensitive on/off mechanism is prone to failure if the device is parked in an unusual position. For example, if I put it in it's protective case, and then toss it into my toolbox face up, it will remain on. Even if you stored the caliper 'face up' for a year, it would cost you no more than if you had no switch at all. Net net, battery life would increase because, the caliper would be turned off for a far longer time than it would be turned on. This is what happens when we lose sight of the original problem that we're trying to solve. The problem is that the calipers have a short battery life mostly because they don't really turn off and secondarily because the dropout voltage is too high to use cheap alkaline batteries. Turning the calipers off (actually in standby) for a year won't do much, when the operating current is 14.5uA and the off current is 13.5uA. Er. Jeff? I was talking about the open circuit represented by a 'position' switch. Off current would be *far* lower than 13.5 uA. It would also prevent me from using in the face down position. I was appalled that I can't use my blender upside down too, until I realized that I never have a need to do that. You need to contact a product liability attorney, and sue for damages resulting from inverted operation. Be sure to mention that there was no warning in the user manual about inverted operation. I've used calipers and other measuring instruments in probably every orientation possible. If the calipers turned off while I was making measurements in a contortionists position, I would be rather irritated. What proportion of the time do you measure with the display facing down? For me it is a very tiny amount of time. Like seconds-per-decade. I own seven pairs of calipers, two of which are dial, two of which are solar, two of which are very cheap digitals and one is a vernier. Of them, only the cheap digitals would benefit from this conversion. I would select the proper measuring tool for the job. You do as well, I trust. Please don't suggest an inertial on/off mechanism (shake to operate). Bouncing around in my car will probably turn it on. If you drive your car 24/365, you have much bigger efficiency worries than a $1.00 cell! True. Also, if I don't drive the car at all, I get an infinitely large gasoline mileage. Both extremes are worthless. I dunno. The 24/365 commute places an upper limit on the amount of time that the calipers would remain powered up. It probably would cost you say $1.20 a year to leave them 'rightside up' in your toolbox. I don't think of this as a huge toll, somehow. Perspective! I non-cleverly installed a "shake to unlock" (iShakeLock) application on my iPhone 3G. The standard method of unlocking the phone requires both hands. I figured that one handed unlocking would be better. The problem was that it kept unlocking in my pocket. Battery life deteriorated rapidly. So, I dumped the app. You keep your iPhone next to your calipers in your pocket? Don't the pointy 'inside' anvils smart a bit? --Winston--Tell me about your pocket lint. |
#117
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
On Nov 27, 5:08*pm, Winston wrote:
Jeff Liebermann wrote: On Sun, 27 Nov 2011 10:45:00 -0800 (PST), wrote: But then the caliper forgets its "zero" every two minutes. *That's very annoying. Mine doesn't. *The initial position is apparently stored in the circuitry. *I can also set it to any position, turn it off, and it will read the same value when turned back on. *One of the benefits of having it draw power continuously. The problem is that it's a much more complicated design, much more than a metalworking hobbyist could reasonably tackle to upgrade his HF cheapies. Retrofits are always more complicated. *I tend to think in terms of new product designs. *If this were for a retrofit or modification, the design philosphy would certainly be different. If we're designing calipers from scratch, we'd just design them for 2uA total draw, not add an outboard switcher with Iq=2uA, then add a timer to turn it off. Agreed. *At 2uA, it probably wouldn't need an on/off switch. I still think that wind up power would be more interesting. Yep, that's still intriguing. *As a practical matter, how do you turn spring tension into 15uA / 1.55V? *A generator, an escapement, a coil and a magnet I suppose. *Time to call a watchmaker. Pancake PM generator which offers the highest velocity at the edge. Basically a magnetized disk and a stator coil. *Spring loaded spool parallel to the pancake motor and the same size. * Ratchet to control direction. *Inertial clutch and some plastic gears between the spool and the pancake motor. *Much like a generator powered flashlight. Pull on the string and the spool spins, which causes the generator to run, charging a super-cap. *If a pull string is too crude, a spiral mainspring mechanism can be added. *If the pull string and generator are too sophisticated, a moving magnet inside a coil, that you shake back and forth to charge the super-cap, much like in some battery-less flashlights. *Maybe a thumb wheel for spinning the pancake generator might better. *Plenty of options. How about a weighted leaf switch in series with the cell? * It could take the form of a thicker 'battery door'. The bulk bypass caps in the caliper would hopefully maintain power during vibration glitches and overhead measurements. Place the caliper 'display down' and power is removed. --Winston--Cheap! Quick! Decent! How about this as a retrofit to the Harbor Freight cheapies: push a pushbutton switch, which charges a supercap when you need it, giving an hour or so runtime per press? Iq = 0uA. Battery life: Same as shelf life. Parts list: homemade switch, supercap. $0.20. Caliper starts blinking? Press the button again to keep it going. -- Cheers, James Arthur |
#118
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
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#119
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
On Nov 28, 2:43*pm, Winston wrote:
wrote: (...) Decent! *How about this as a retrofit to the Harbor Freight cheapies: push a pushbutton switch, which charges a supercap when you need it, giving an hour or so runtime per press? * *Iq = 0uA. * *Battery life: Same as shelf life. * *Parts list: homemade switch, supercap. *$0.20. Caliper starts blinking? *Press the button again to keep it going. I like that! *But I can reduce the BOM size. Just a (rotary?) switch in the battery cover. If you leave it on, you get 10 months out of the battery. If you use the power switch religiously, you get 'shelf life'. * A switch handling ~40 uA does not have to * *be nearly as stout as one handling 'short circuit' * *current into the super cap. Low-current switches can be a bear--the contacts oxidize. Gold fixes that generally, IIRC. * Most super caps don't tolerate high current well. No problem here. The low battery voltage and high internal resistance of these tiny cell-phone super caps limits the current nicely. * This mod is dead simple, reversible and does not * *require access to a ground connection. I like some sort of dead-man timer better. It could be just a low threshold mosfet with a gate cap which you charge, and a *large* discharge resistor(*) so it times out. That guarantees the battery- saving feature even if you forget. (*) (From the jellybean / junkbox standpoint, the discharge "resistor" might be a reverse-biased rectifier's leakage.) But yes, just adding a real switch is a huge improvement over not having it. A real switch also lets you hold the zero setting over night if you want to. I sometimes do that with the lathe, if, for example, I'm in the middle of something when it's time to turn in. You *do* need access to the underside of the cell, since that's where the (-) contact is. Insert a very thin piece of double-sided printed circuit mat'l, wire a tiny slide switch to both sides of that, and Bob's yer uncle. That's reversible, and if you're a brute, you can even hang the switch outboard by the wires. That way there's no modification of the caliper needed at all. That's good enough and simple enough that I'll put 'er on the list. I've got maybe a dozen of these (two on the lathe alone), and it'd be nice not pulling the batteries (as I do now). -- Cheers, James Arthur |
#120
Posted to rec.crafts.metalworking,sci.electronics.design,sci.electronics.repair
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Repaired Harbor Freight digital caliper
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