Wow, Thanks for all the help.
Work (a definite 4 letter word) has kept me away for several weeks, but I will be able to get home this weekend and give it a try.
Can it really be so simple.
lonewoof I think there's an easier way to accomplish this: Geez, why didn't I think of that! Sometimes the obvious is just too simple. Thanks for the solution.Joe /Lone
I think there's an easier way to accomplish this:
Geez, why didn't I think of that! Sometimes the obvious is just too simple. Thanks for the solution.
Joe
/Lone
Yup - That'll work !
I was obviously over-thinking it !
Mark.
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ
Remember: In South Carolina, North is southeast of Due West... HIOAg /Bill
I have used 5 volt logic chips for this in some single target signals using 3mm bi-color LED's. I did this for our club layout with the older DC block system a number of years ago. I found the idea a number of years ago in an older N Scale magazine.
Just a common TTL inverter chip. I used what resistors I had in the junk box. You might adapt this to your circuit.
The CMOS chips use up to 12 volts DC. There are many on line surplus chip companies and you could find some on ebay also.
A couple CMOS chips with multiple inverters would work.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
I did some experimenting last night, and I believe I found the solution ....
You will need a bi-polar power source for it to work with the 2-legged LEDs though. You could build one from two 12 volt wall-warts (which is what I used) if they are rated high enough for all you current draw (which shouldn't be much really.
Take the positive of one transformer (wall wart) and the negative of the other and tie them together - this will become your "common" or neutral power source in addition to the positive and negative. The neutral will become negative or positive biased depending on whether the opposite source is either negative or positive biased which is what happens on pin 3 of the IC.
Use the positive and negative supply as per norm to power the circuit. Connect the neutral to one leg of the LED through a 1000 ohm resistor and the other leg to pin 3 of the IC. You will have to test the LED for proper color orientation - if it works backwards to how you want, just reverse the leads.
This concept worked as a "bench test", so it should work within this circuit.
There's just no way for a simple substitution in that circuit. The EASIEST thing to do would be to replace the SPDT relay with a DPDT relay and use the second set of contacts to control the bi-color LED. A DPDT relay with otherwise the same ratings should be only a little more expensive than the SPDT.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
I wasn't refering to his circuit, just that there is a source for the LED's There actually isn't a circuit needed. You could just switch voltage to the LED's with the appropriate dropping resistor.
Springfield PA
Mark R. Hamltnblue You can definitely do a tri color LED or 2 color with 3 wires. I have one of the tomar search lights and it works great. Look for search light signals on this site: You can also get just the LED's on the site. https://tomarindustries.com/signals.htm Did you look carefully at the schematic for the circuit. The "common" connection to both leads will be either negative or positive (high or low) depending of the state of pin 3 on the IC. The common pin on a 3-legged LED is either negative OR positive (yes, there are both) - but will only function on the one polarity it's designed for - NOT a polarity reversing common as this circuit requires by design. Mark.
Hamltnblue You can definitely do a tri color LED or 2 color with 3 wires. I have one of the tomar search lights and it works great. Look for search light signals on this site: You can also get just the LED's on the site. https://tomarindustries.com/signals.htm
You can definitely do a tri color LED or 2 color with 3 wires. I have one of the tomar search lights and it works great. Look for search light signals on this site: You can also get just the LED's on the site.
https://tomarindustries.com/signals.htm
Did you look carefully at the schematic for the circuit. The "common" connection to both leads will be either negative or positive (high or low) depending of the state of pin 3 on the IC. The common pin on a 3-legged LED is either negative OR positive (yes, there are both) - but will only function on the one polarity it's designed for - NOT a polarity reversing common as this circuit requires by design.
Mark,
Good point. It is always scary when the wrong answers to questions like this are added to a thread. Your answer will keep everyone on the right track, so to speak.
Alton Junction
Thanks for the quick response Joe and Mark. As you have pointed out Mark, the problem is the switching polarity of the middle contact. I had thought about using a relay but space is limited , I would need 18 of them). I have got to thinking about using a zenner diode to drop the +ve voltage applied to a Bi-colour (2 leg) from the +ve rail. would that give me one colour (say red) when pin 3 is low, whilst giving me a +ve bias in reverse when pin 3 is high, so giving me a current flow through the second colour of the LED. What do you think? I know the idea needs something else to make it work, can anyone help?
Even a three-legged LED won't work on that circuit as a direct replacement.
The only "simple" option would be to use DPDT relays instead of SPDT and use the extra contacts on the relay to control the LED utilizing a common input on a three legged LED (3mm commonly available through Digikey, Mouser, ebay, etc.)
To utilize a two-legged LED off the relay, you would need DPDT contacts JUST for the LED (wired like a typical reversing switch to flip the polarity to the LED)
Two lead bicolor leds won't work in this circuit since they are actually a red and a green led wired anti-parallel and contained in the same capsule. They work by swapping the polarity of the leads. My guess is that without some serious modification of the circuit you are going to need three lead leds. Sorry that I can't be of more help.
Hi there,
I have spent many hours looking through people's postings and have learnt more than I thought possible from other problems, so a big thanks to all those who are prepared to help us unfortunates who are lacking in the knowledge department.
I have a problem which I'm hoping someone will be able to solve for me.
I have built several signal circuits as shown on the 'Electronics Club' site http://www.kpsec.freeuk.com/projects/signal.htm
I want to use them as part of an switch indicator panel but to do this neatly I ned to use a single Bi-colour LED in place of the red/green individuals. There are 3 wires but no common! the annode of one LED is connected to the cathode of the other, I guess the output of the 555 goes either high or low to drive the corrisponding LED? is that right?
Can someone please help me to find a way of replacing these. Using 2 wire bi-colours would be great as the 3mm ones I can get hold of seem to all be 2 wire.
Many thanks in advance to the helpful people out there.