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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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#1
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Timing Circuit
I need to design a circuit that I can tell it to start (digitally), and
then it will tell me when 10 minutes have passed. I just need to be pointed in the right direction. What's the difference bewteen a timer/clock/counter. I have a good understanding of circuit theory but does anyone know of a good IC that can be surface mounted (and is cheap) that I shoulod use. Any help or tips are greatly appreciated |
#2
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Timing Circuit
wrote in message ups.com... I need to design a circuit that I can tell it to start (digitally), and then it will tell me when 10 minutes have passed. I just need to be pointed in the right direction. What's the difference bewteen a timer/clock/counter. I have a good understanding of circuit theory but does anyone know of a good IC that can be surface mounted (and is cheap) that I shoulod use. Any help or tips are greatly appreciated All depends on how accurate that you need to be really. A simple timer circuit - the CMOS version of the good old 555 is quite capable of this sort of delay - could be set up fairly precisely in monostable mode, to do 10 minutes or thereabouts, say give or take a few seconds. If you really need an accurate 10 minutes, then you need to use a counter. You would start with a clock generator, probably a standard watch crystal at 32.768kHz, then divide it down to get your 10 minute interval. If you don't want to divide as far, you can start with a lower frequency, but it's usually convenient to use a ' binary ' frequency. A 16 bit counter on the end of a 32k clock, will get you down to a second. You then need a further 10 bits of counter and a bit of AND-ing to get you to the 10 minutes. You could also pick a ' custom ' frequency for the clock to suit your final time, which saves the gates at the end. Horses for courses really Arfa |
#3
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Timing Circuit
wrote in message ups.com... I need to design a circuit that I can tell it to start (digitally), and then it will tell me when 10 minutes have passed. I just need to be pointed in the right direction. What's the difference bewteen a timer/clock/counter. I have a good understanding of circuit theory but does anyone know of a good IC that can be surface mounted (and is cheap) that I shoulod use. Any help or tips are greatly appreciated buy a cheap cooking timer http://www.maplin.co.uk/Module.aspx?...130&doy=search |
#4
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Timing Circuit
Arfa Daily spake thus:
wrote in message ups.com... I need to design a circuit that I can tell it to start (digitally), and then it will tell me when 10 minutes have passed. I just need to be pointed in the right direction. What's the difference bewteen a timer/clock/counter. I have a good understanding of circuit theory but does anyone know of a good IC that can be surface mounted (and is cheap) that I shoulod use. Any help or tips are greatly appreciated All depends on how accurate that you need to be really. A simple timer circuit - the CMOS version of the good old 555 is quite capable of this sort of delay - could be set up fairly precisely in monostable mode, to do 10 minutes or thereabouts, say give or take a few seconds. If you really need an accurate 10 minutes, then you need to use a counter. You would start with a clock generator, probably a standard watch crystal at 32.768kHz, then divide it down to get your 10 minute interval. If you don't want to divide as far, you can start with a lower frequency, but it's usually convenient to use a ' binary ' frequency. A 16 bit counter on the end of a 32k clock, will get you down to a second. You then need a further 10 bits of counter and a bit of AND-ing to get you to the 10 minutes. Since it looks like 32.768 kHz is the lowest-frequency oscillator available (checked both Digikey & Jameco), I'd say all you need would be one of them (a complete oscillator, not a crystal) and 2 counter chips (like the 74HCT4040), one set to divide/16 as you explained, the other /10. This would give you a TTL pulse at the end of the countdown cycle. -- The only reason corrupt Republicans rule the roost in Washington is because the corrupt Democrats can't muster any viable opposition. |
#6
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Timing Circuit
In article ,
Fred McKenzie wrote: There is an IC that might get you started, the NE-555. Other sources make it, but always with the "555" number. This chip can be configured to start timing on command, and charge-up a capacitor through a resistor, until a preset time has past. At that point it should reset and generate an output pulse or level shift. The trouble with this approach is that it is best for short time delays. Ten minutes is a relatively long time, so circuit leakage may cause the delay to be longer than what you would calculate based on the R-C time constant. If you use the CMOS version - usually 7555 - the low current allows times of much more than 10 minutes. -- *Even a blind pig stumbles across an acorn now and again * Dave Plowman London SW To e-mail, change noise into sound. |
#7
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Timing Circuit
Dave Plowman (News) wrote:
The trouble with this approach is that it is best for short time delays. Ten minutes is a relatively long time, so circuit leakage may cause the delay to be longer than what you would calculate based on the R-C time constant. If you use the CMOS version - usually 7555 - the low current allows times of much more than 10 minutes. The problem is that you end up needing absurd component values - ten minutes delay would need 1.2Mohms and 470mf, for example, and the latter is likely to be inaccurate and probably variable. You can use two of them (or a 556), or there used to be a chip that would work up to many hours delay, the number of which I cannot recall; I think it was a TDA- something. -- rgds LAurence ....Enter any 12-digit prime number to continue. ---*TagZilla 0.059* http://tagzilla.mozdev.org |
#8
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Timing Circuit
Laurence Taylor spake thus:
Dave Plowman (News) wrote: The trouble with this approach is that it is best for short time delays. Ten minutes is a relatively long time, so circuit leakage may cause the delay to be longer than what you would calculate based on the R-C time constant. If you use the CMOS version - usually 7555 - the low current allows times of much more than 10 minutes. The problem is that you end up needing absurd component values - ten minutes delay would need 1.2Mohms and 470mf, for example, and the latter is likely to be inaccurate and probably variable. You can use two of them (or a 556), or there used to be a chip that would work up to many hours delay, the number of which I cannot recall; I think it was a TDA- something. Why would you want to mess with a 555 at all? Not precise, and more complicated. I already posted a possible solution using an oscillator (1MHz) and two 74HCT4040 chips, which will give you an *exact* time and uses fewer components. (Like no resistors or capacitors, except for maybe one 0.01 uf bypass cap.) -- If the United States government, with all its capacity to collect and interpret information, did not see Hamas doing very well in the Palestinian election in the wake of these other Islamist victories, then it is either willfully blind or totally incompetent—- and neither possibility is a very comforting thought. - Rami G. Khouri, editor at large of the Beirut-based _Daily Star_ |
#9
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Timing Circuit
Laurence Taylor wrote: Dave Plowman (News) wrote: The trouble with this approach is that it is best for short time delays. Ten minutes is a relatively long time, so circuit leakage may cause the delay to be longer than what you would calculate based on the R-C time constant. If you use the CMOS version - usually 7555 - the low current allows times of much more than 10 minutes. The problem is that you end up needing absurd component values - ten minutes delay would need 1.2Mohms and 470mf, for example, and the latter is likely to be inaccurate and probably variable. You can use two of them (or a 556), or there used to be a chip that would work up to many hours delay, the number of which I cannot recall; I think it was a TDA- something. -- rgds LAurence Well letcher laurence.... Does everyone know that you are a pedophile? laurence likes to **** children..... alt.support.boy-lovers |
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