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Electronics Q
A different type of DIY.
Im trying to make a modal railway crossing with flashing red Leds. Iv'e got some flashing leds and some ordinary ones, cant use two flashing leds together as the flash rate and sequence is wrong, so I had hoped to use one flashing led to drive another ordinary led. But ^&%^&% if I can make it work, if anyone can come up with a simple solution I would be most grateful. PS I know there are lots of methods of doing this from ic555 ic4011 or even two transistor oscillators, but that's not KISS enough for me. |
On Sat, 29 Jan 2005 20:17:11 GMT, "F-Red"
wrote: A different type of DIY. Im trying to make a modal railway crossing with flashing red Leds. Iv'e got some flashing leds and some ordinary ones, cant use two flashing leds together as the flash rate and sequence is wrong, so I had hoped to use one flashing led to drive another ordinary led. But ^&%^&% if I can make it work, if anyone can come up with a simple solution I would be most grateful. PS I know there are lots of methods of doing this from ic555 ic4011 or even two transistor oscillators, but that's not KISS enough for me. There's (was?) a dedicated LED flasher chip, the LM3909. Dead simple to use! Frank Erskine MJBC, OETKBC |
What about
http://www.kpsec.freeuk.com/proj.htm http://wild-bohemian.com/electronics/flasher.html http://ourworld.compuserve.com/homep...n/homepage.htm "F-Red" wrote in message 4... A different type of DIY. Im trying to make a modal railway crossing with flashing red Leds. Iv'e got some flashing leds and some ordinary ones, cant use two flashing leds together as the flash rate and sequence is wrong, so I had hoped to use one flashing led to drive another ordinary led. But ^&%^&% if I can make it work, if anyone can come up with a simple solution I would be most grateful. PS I know there are lots of methods of doing this from ic555 ic4011 or even two transistor oscillators, but that's not KISS enough for me. |
F-Red wrote:
I had hoped to use one flashing led to drive another ordinary led. No chance, I'm afraid: the electronics do do the flashing are all sealed up inside the body of the flashing LED; even when it's not flashing, it's wanting to draw a little bit of current for the flashing circuit, so you can't just put an ordinary LED in series with a flashing one and expect it to light up in 'sympathy' with the flasher. You'll just have to bite the bullet and knock up the simplest 555 timing circuit you can (very few external components needed: two resistors, one capicitor, one more capacitor for glitch-free running). A super-simple circuit diagram appears at http://www.hilaroad.com/camp/projects/electron5.html and Googling with "555 flasher" throws up hundreds of similar ones. You'd put your two LEDs, each with their own current-limiting resistor, where these circuits show a single LED, if you want them both flashing ON at the same time. |
In article ,
Frank Erskine wrote: There's (was?) a dedicated LED flasher chip, the LM3909. Dead simple to use! Or a voltage regulator, like the LM78 -- *Caution: I drive like you do. Dave Plowman London SW To e-mail, change noise into sound. |
In article ,
"F-Red" writes: A different type of DIY. Im trying to make a modal railway crossing with flashing red Leds. Iv'e got some flashing leds and some ordinary ones, cant use two flashing leds together as the flash rate and sequence is wrong, so I had hoped to use one flashing led to drive another ordinary led. But ^&%^&% if I can make it work, if anyone can come up with a simple solution I would be most grateful. What happens if you connect a flashing LED in series with an ordinary LED? Maybe the off-state current is still enough to light the other LED? Also, what supply voltage to you have to hand, and do you know the part number of the flashing LED? -- Andrew Gabriel Consultant Software Engineer |
PS I know there are lots of methods of doing this from ic555 ic4011 or even two transistor oscillators, but that's not KISS enough for me. Maplins do/used to do, a 2 x transister flashing led kit. Used one for my outside alarm box. Dave -- For what we are about to balls up may common sense prevent us doing it again in the future!! |
F-Red wrote:
A different type of DIY. Im trying to make a modal railway crossing with flashing red Leds. Iv'e got some flashing leds and some ordinary ones, cant use two flashing leds together as the flash rate and sequence is wrong, so I had hoped to use one flashing led to drive another ordinary led. But ^&%^&% if I can make it work, if anyone can come up with a simple solution I would be most grateful. Should work. You connect the flashing LED in series with the ordinary one (it'll need 2-4V (red-blue) more to work. What happens? |
In article , Andrew Gabriel
writes In article , "F-Red" writes: A different type of DIY. Im trying to make a modal railway crossing with flashing red Leds. Iv'e got some flashing leds and some ordinary ones, cant use two flashing leds together as the flash rate and sequence is wrong, so I had hoped to use one flashing led to drive another ordinary led. But ^&%^&% if I can make it work, if anyone can come up with a simple solution I would be most grateful. What happens if you connect a flashing LED in series with an ordinary LED? Maybe the off-state current is still enough to light the other LED? I think you have the right idea andrew, a quick look at some flashing LED data shows some latitude in the supply voltage (9-12V) so should work from a 12V supply with an LED in series. A resistor in parallel with the slave LED will allow some quiescent flow without it lighting, 1k would let 1mA flow w/o any risk of lighting. 20mA seems to be a typical ON current. A possible problem is that the flasher chip will see its voltage change from ~10 when both LEDs are on to ~12 when both are dark which may upset it, so it is one to suck and see. Other risks are intensity, spread & colour matching. -- fred |
Ian Stirling
F-Red wrote: A different type of DIY. Im trying to make a modal railway crossing with flashing red Leds. Iv'e got some flashing leds and some ordinary ones, cant use two flashing leds together as the flash rate and sequence is wrong, so I had hoped to use one flashing led to drive another ordinary led. But ^&%^&% if I can make it work, if anyone can come up with a simple solution I would be most grateful. Should work. You connect the flashing LED in series with the ordinary one (it'll need 2-4V (red-blue) more to work. What happens? Thank's for everyone replies, but the LEDs have to flash in sequence, one on other off. Just like on a real crossing ! I had hoped to do this with *ONE* transistor, ie bias for base being supplied by resistor/ Flashing led junction. But that don't work because they both flash together. I shall have to go to bed tonight and dream about this, that always provides a solution. |
In article ,
"F-Red" writes: Thank's for everyone replies, but the LEDs have to flash in sequence, one on other off. Just like on a real crossing ! I had hoped to do this with *ONE* transistor, ie bias for base being supplied by resistor/ Flashing led junction. But that don't work because they both flash together. I shall have to go to bed tonight and dream about this, that always provides a solution. Ah -- I was thinking you wanted them on together. Try something like this: +ve ---------------- | | | / --- \ \ / flasher / 680 ohms --- \ | | | ------ | NPN | | | |/ | |------| --- | |\| \ / LED / -| --- 100 \ | | ohms/ | | \ | | | | | | | | 0v -------------------- Any small low gain NPN transistor should do here which can handle, say, 20mA base current, e.g. BC635, BC639 (or BC546, BC547 but their gain is a bit high). If the separate LED does not switch right off, reduce the value of the 100 ohm resistor. Adjust the 680 ohm resistor if the two LEDs are different brightness. -- Andrew Gabriel |
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On Sat, 29 Jan 2005 23:46:15 GMT, "F-Red"
wrote: Ian Stirling F-Red wrote: A different type of DIY. Im trying to make a modal railway crossing with flashing red Leds. Iv'e got some flashing leds and some ordinary ones, cant use two flashing leds together as the flash rate and sequence is wrong, so I had hoped to use one flashing led to drive another ordinary led. But ^&%^&% if I can make it work, if anyone can come up with a simple solution I would be most grateful. Should work. You connect the flashing LED in series with the ordinary one (it'll need 2-4V (red-blue) more to work. What happens? Thank's for everyone replies, but the LEDs have to flash in sequence, one on other off. Just like on a real crossing ! Do you have barriers that come down in sequence as well? I had hoped to do this with *ONE* transistor, ie bias for base being supplied by resistor/ Flashing led junction. But that don't work because they both flash together. I shall have to go to bed tonight and dream about this, that always provides a solution. That could produce a short circuit.... -- ..andy To email, substitute .nospam with .gl |
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Andy Hall
Thank's for everyone replies, but the LEDs have to flash in sequence, one on other off. Just like on a real crossing ! Do you have barriers that come down in sequence as well? Oh yes, and a little amber Led that comes on first, triggered by an approaching train. |
I think this is the premade unit from CPC, http://cpc.farnell.com/jsp/endecaSearch/partDetail.jsp?SKU=SR00227&N=401, not sure though as there's no picture. I might have a flick through the catalogue to confirm if I can be arsed to go and get it! Hi Lurch No, mine was bought ages ago as a kit. Bit of a admission as I work 5 days a week in electronics, but it was cheaper than designing, making a pcb etc etc. CU Dave -- For what we are about to balls up may common sense prevent us doing it again in the future!! |
On Sun, 30 Jan 2005 00:56:07 GMT, "F-Red"
wrote: Andy Hall Thank's for everyone replies, but the LEDs have to flash in sequence, one on other off. Just like on a real crossing ! Do you have barriers that come down in sequence as well? Oh yes, and a little amber Led that comes on first, triggered by an approaching train. Impressive. Bells as well? Presumably with this level of attention to detail, you also try to operate the trains at scale speed. I once worked out that the average child operates their train set (as opposed to model railway) at a scale speed of over 300mph - and we are talking about a steam tank engine. A philosophical thought for you: So for the flashing LEDs, do you think it's most appropriate to operate them at the same speed as in real life, scaled down to the scale speed of the trains, or faster on the principle that the heart of a small animal beats more quickly than that of a large one? -- ..andy To email, substitute .nospam with .gl |
Maybe rather than KISS, make it complex... How's your software experience?,
how's your son's? One dead simple solution from the point of view of number of soldered connections would be to use a little PIC micro-controller; These can drive LEDs directly, and with sufficient software nounce you can get it to do whatever you need. Could be fun for the sprog too (dunno if you mentioned his age?) Regards "F-Red" wrote in message . .. Andy Hall Thank's for everyone replies, but the LEDs have to flash in sequence, one on other off. Just like on a real crossing ! Do you have barriers that come down in sequence as well? Oh yes, and a little amber Led that comes on first, triggered by an approaching train. |
On Sat, 29 Jan 2005 23:46:15 GMT, F-Red wrote:
Thank's for everyone replies, but the LEDs have to flash in sequence, one on other off. Just like on a real crossing ! I had hoped to do this with *ONE* transistor, I think it should be possible with one Tr but failing that an astable multivibrator will certainly do it. http://www.play-hookey.com/digital/e...l_astable.html Scroll down for the circuit diagram, the good 'old 555 timer chip can perform this operation. Or you could buy a Brio level crossing that has two poles with alternate flashing LEDs, bell sound and gates that drop all triggered by the coupling magnets closing reed relays. -- Cheers Dave. pam is missing e-mail |
On Sun, 30 Jan 2005 09:08:43 +0000, Dave Stanton
strung together this: I think this is the premade unit from CPC, http://cpc.farnell.com/jsp/endecaSearch/partDetail.jsp?SKU=SR00227&N=401, not sure though as there's no picture. I might have a flick through the catalogue to confirm if I can be arsed to go and get it! Hi Lurch No, mine was bought ages ago as a kit. Bit of a admission as I work 5 days a week in electronics, but it was cheaper than designing, making a pcb etc etc. Sorry, I meant if the OP was after so simple it was simpler than simple itself you can get pre-made LED flasher units for bell boxes that flash alternately, which I think was at the end of the link, all you need to do is stick 12VDC on it and that's it. -- SJW Please reply to group or use 'usenet' in email subject |
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"F-Red" wrote in message 4... A different type of DIY. Im trying to make a modal railway crossing with flashing red Leds. Iv'e got some flashing leds and some ordinary ones, cant use two flashing leds together as the flash rate and sequence is wrong, so I had hoped to use one flashing led to drive another ordinary led. But ^&%^&% if I can make it work, if anyone can come up with a simple solution I would be most grateful. PS I know there are lots of methods of doing this from ic555 ic4011 or even two transistor oscillators, but that's not KISS enough for me. Surely a simple 2 transistor multivibrator (flip flop) with the leds in the loads would suffice, it would have the advantage that you could set the frequency and the mark to space ratio as you require. 2 transistors, 2 capacitors, 2 resistors, 2 leds(non flashing ) Cheers Tom |
Mike Dodd wrote:
Maybe rather than KISS, make it complex... How's your software experience?, how's your son's? One dead simple solution from the point of view of number of soldered connections would be to use a little PIC micro-controller; These can drive LEDs directly, and with sufficient software nounce you can get it to do whatever you need. Yup, could be fun... I once had a ten page requirement spec come in from one of the bods on a hardware team (big defense contractor) to write software for a pair of flashing LEDs! They had an azimuth and elevation meter, with a couple of analogue dials that indicated the position of a steerable turret under a helicoptor. They wanted an enhancement to have an LED flash when an endstop was reached on each axis. They had arranged to send a single byte command down a serial link to the meter, and then use a microcontroller in the back of the (small) meter to decode it and flash/light the required LEDs. Since they were short of space they used a "micropack" 8031 based controller, these where seriously expensive beasties (600 quid a shot at the time) with all the supporting circuitry and the 8031 all built on one substrate - just add power. Anyway, did the software for them (about 3 days work by the time all the documentation and QA stuff was done), and then to rub salt into the wound suggested an alternate design for the same functionality, using a hard wired UART, a PAL, and an astable at a total cost of under a tenner! (compared to what must have worked out at something getting on for 1.5 grand per LED, given the customer was only buying three meters!) -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
In article ,
"F-Red" writes: (Andrew Gabriel) Ah -- I was thinking you wanted them on together. Try something like this: Hmm that's were I started :-? Current flows to tr/base when flashing led is ON ;-( Indeed, which switches the other LED off. It was after my last post that I had that penny-dropping DOH! Moment. Works fine now, one flashing led, one ordinary led, one transistor, and two resistors, KISS ! Glad it works. If I'd had a flashing LED, I would have tried it before posting, but I don't;-) Incidently, if you're running it from a battery supply, the addition of a second transitor and resistor could knock a third off the current consumption. Im building this level crossing for a 19-year-old nephew who is severely disabled after an accident, the mental and physical stimulus of operating a train layout is helping enormously in his recovery. Best of luck with it. -- Andrew Gabriel |
"Tom"
PS I know there are lots of methods of doing this from ic555 ic4011 or even two transistor oscillators, ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Surely a simple 2 transistor multivibrator (flip flop) with the leds in the loads would suffice, it would have the advantage that you could set the frequency and the mark to space ratio as you require. 2 transistors, 2 capacitors, 2 resistors, 2 leds(non flashing ) Cheers Tom Yes but I had already built the board to control the level crossing, with no spare room for adaptations. For simplicity sake I was going to use two flashing leds per signal post x4 until I realised that the flash timing looked unrealistic. So I had a space of about 5mm x 5mm within each post to birds-nest in something that worked, which this does superbly. And it scores higher on the KISSometer than any other design i've seen. -- F-Red |
Sorry, I meant if the OP was after so simple it was simpler than simple itself you can get pre-made LED flasher units for bell boxes that flash alternately, which I think was at the end of the link, all you need to do is stick 12VDC on it and that's it. Got ya ! Dave -- For what we are about to balls up may common sense prevent us doing it again in the future!! |
On the subject of flashing LEDs, anyone know of a low power consumption
slow flashing all in one? For a car burglar alarm where the existing one - built into an external sensor didn't flash, but the one I've fitted from IIRC Maplin is very bright with about a 50% duty cycle, but draws too much current on a car which isn't used every day. And there's no room inside the sensor to add any circuitry. Something like one flash every 10 seconds would be ideal. -- *If all the world is a stage, where is the audience sitting? Dave Plowman London SW To e-mail, change noise into sound. |
Dave Plowman (News) wrote:
On the subject of flashing LEDs, anyone know of a low power consumption slow flashing all in one? I don't, nor does the RS catalogue: the integral-flasher types I see there all quote a consumption of give-or-take 40mA; galling when there are 'high-efficiency' LEDs pulling as little as 2mA, and a CMOS 555 could readily have high-value Rs and a 10microF tant to give the slow, low-duty-cycle flashing you want, if only there were room. However, it's not clear to me that it's the LED which is the main culprit in your alarm discharging the rarely-charged battery - have you had a chance to measure the whole alarm's draw, with and without the LED connected? 40mA times 24hours would be 1AH, so a week's draw for the LED alone wouldn't be more than 7AH - which should be well within the realms of 'trivial' for a typical car battery of claimed 50-80AH. Maybe a little solar trickle-charger, or maximally-convenient way of connecting a mains lead-acid charger (with decent charging control), would meet the overall requirement? |
On Mon, 31 Jan 2005 10:07:02 +0000 (GMT), Dave Plowman (News) wrote:
Something like one flash every 10 seconds would be ideal. Have a look on RS/Maplin for a flashing LED driver chip (8 pin DIP). I fitted one to my old Escort (old as in '85ish) as a deterant(*) flashes at about that rate but as a bright pulse, takes very little current as it charges a C which it then discharges through the LED. google LM3909 is the chip datasheet at: http://www.solarbotics.net/library/d...ts/default.htm Not found by Maplin, RS, CPC or Farnell, discontinued due to age I suspect. B-( (*) Probably worked, the car was stolen when the LED wasn't flashing for some reason... -- Cheers Dave. pam is missing e-mail |
"Dave Plowman (News)"
On the subject of flashing LEDs, anyone know of a low power consumption slow flashing all in one? For a car burglar alarm where the existing one - built into an external sensor didn't flash, but the one I've fitted from IIRC Maplin is very bright with about a 50% duty cycle, but draws too much current on a car which isn't used every day. And there's no room inside the sensor to add any circuitry. Something like one flash every 10 seconds would be ideal. Don't know of one, but you could build a circuit to you own requirements that will run for a year on a 1.5v battery. http://discovercircuits.com/PDF-FILES/1vled3.pdf so even if the car battery is being drained by something else and goes flat, the LED keeps flashing. I know you said "no room inside the sensor" but only two wires from led need to go into the sensor. -- F-Red |
In article om,
Dave Liquorice wrote: Something like one flash every 10 seconds would be ideal. Have a look on RS/Maplin for a flashing LED driver chip (8 pin DIP). I fitted one to my old Escort (old as in '85ish) as a deterant(*) flashes at about that rate but as a bright pulse, takes very little current as it charges a C which it then discharges through the LED. Snag is the LED is part of the motion detector assembly which has no spare room inside for extra components. The original was a non flashing very dim LED which I replaced with a very bright all in one with a 50% duty cycle. I'd prefer one just as bright, but a slower flash rate. The factory fit one on my other car flashes about every ten seconds. -- *Gaffer tape - The Force, light and dark sides - holds the universe together* Dave Plowman London SW To e-mail, change noise into sound. |
In article ,
F-Red wrote: I know you said "no room inside the sensor" but only two wires from led need to go into the sensor. Snag is the sensor mounting is hinged, and the cable goes through the hinge. Would be possible to change it for one with more cores, but difficult. And the sensor is mounted on a removable parcel shelf so is plugged in - that would have to be changed too. ;-) -- *If they arrest the Energizer Bunny, would they charge it with battery? * Dave Plowman London SW To e-mail, change noise into sound. |
On Mon, 31 Jan 2005 15:24:50 GMT, F-Red wrote:
Don't know of one, but you could build a circuit to you own requirements that will run for a year on a 1.5v battery. http://discovercircuits.com/PDF-FILES/1vled3.pdf All those parts... the LM3909 t run from 12v has just the chip, 2 Rs, and a C... I know you said "no room inside the sensor" but only two wires from led need to go into the sensor. My thoughts as well, normally plenty of space behind trim panels. I don't think Dave will find a pulse type flashing LED, they generally need a decent sized C to store the charge, difficult to manufacture on a bit of silicon. B-) -- Cheers Dave. pam is missing e-mail |
Dave Liquorice wrote:
My thoughts as well, normally plenty of space behind trim panels. I don't think Dave will find a pulse type flashing LED, they generally need a decent sized C to store the charge, difficult to manufacture on a bit of silicon. Indeed - though there's no reason-in-principle that the little-bit-of-silicon couldn't have a relatively high-freq oscillator (so minimal C needed), a string of dividers, and finally a counter so as to light the LED on a 1:7, 1:15, or 1:31 duty-cycle... |
On Mon, 31 Jan 2005 19:47:03 +0000, Stefek Zaba wrote:
Indeed - though there's no reason-in-principle that the little-bit-of-silicon couldn't have a relatively high-freq oscillator (so minimal C needed), a string of dividers, and finally a counter so as to light the LED on a 1:7, 1:15, or 1:31 duty-cycle... But with a minimal C where does the energy for the pulse come from? These pulse flashers are just a few mS long at 40mA or more. The amount of light you get from the normal 10 or 20mA of just a few mS duration is pretty dim... -- Cheers Dave. pam is missing e-mail |
Dave Liquorice wrote:
But with a minimal C where does the energy for the pulse come from? Shamelessly drawn from Vcc - I'm happily assuming I can draw the 20mA or so to light the LED load from the powerline, for the brief duration of the lit pulse, without having to accumulate the coulombs myself during the longer unilluminated period. I'm only solving the average current-draw problem with the shorter duty-cycle, not a cycle-long limited current-draw constraint... |
"Dave Liquorice"
On Mon, 31 Jan 2005 15:24:50 GMT, F-Red wrote: Don't know of one, but you could build a circuit to you own requirements that will run for a year on a 1.5v battery. http://discovercircuits.com/PDF-FILES/1vled3.pdf All those parts... the LM3909 t run from 12v has just the chip, 2 Rs, and a C... Er but the 3909 has been obsolete for at least 3 years, you can still get them though. $14 plus postage. You could buy a new Fng alarm for that. ! -- F-Red |
On Mon, 31 Jan 2005 23:09:40 GMT, "F-Red"
wrote: "Dave Liquorice" On Mon, 31 Jan 2005 15:24:50 GMT, F-Red wrote: Don't know of one, but you could build a circuit to you own requirements that will run for a year on a 1.5v battery. http://discovercircuits.com/PDF-FILES/1vled3.pdf All those parts... the LM3909 t run from 12v has just the chip, 2 Rs, and a C... Er but the 3909 has been obsolete for at least 3 years, you can still get them though. $14 plus postage. You could buy a new Fng alarm for that. ! I have a load of LM3909s. In fact a chip just fell to the floor from a "bookshelf" in the living room - it was a 3909 :-) -- Frank Erskine Sunderland |
Frank Erskine
On Mon, 31 Jan 2005 23:09:40 GMT, "F-Red" wrote: "Dave Liquorice" On Mon, 31 Jan 2005 15:24:50 GMT, F-Red wrote: Don't know of one, but you could build a circuit to you own requirements that will run for a year on a 1.5v battery. http://discovercircuits.com/PDF-FILES/1vled3.pdf All those parts... the LM3909 t run from 12v has just the chip, 2 Rs, and a C... Er but the 3909 has been obsolete for at least 3 years, you can still get them though. $14 plus postage. You could buy a new Fng alarm for that. ! I have a load of LM3909s. In fact a chip just fell to the floor from a "bookshelf" in the living room - it was a 3909 :-) Good for you, now for a little gold star, tell me were you can still buy them in the UK and at what price. -- F-Red |
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