The diode should block the negative current, right?
This is the opto isolated circuit that I think was the one purchased...here is the schematic of it (the dual ckt schematic shown here but just one in the relay unit he bought).
When the RSC signal goes to +5, the relay is off (normally closed contact active). When the RSC signal goes to -5, the relay will close (normally open contact active).
BUT when at -5 vdc, the voltage thru the led and opto is double the intended voltage swing which is +5 to GND. So I put the 2.2K resistor in so that the current is not too high for the opto-isolator. So no diode needed actually, but I figured it won't hurt any thing as long as it points the same way as the LED in the input of the circuit.
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One would think that at -5 you'd be reverse biasing the LED internally, and the series diode if you use one, and no current would flow.
Gentlemen,
This is great. I'm going to test the waters and advise. My goal, not to mention having a block signal tied to a Fastrack CC remote switch, is to provide results with everyone who wish to take on this encounter. Thank you. Will advise.
Originally Posted by gunrunnerjohn:
One would think that at -5 you'd be reverse biasing the LED internally, and the series diode if you use one, and no current would flow.
in the same direction as the LED. Not pointing at it but rather the same way.
Pointing in the same direction as the LED, not pointing AT the LED.
Just so we're on the same page, the RSC connection goes to the IN terminal. The top of the LED and Opto diode is +Vcc and gets the +5 volt dc supply. It's hard to see the IN terminal on the schematic unless you click on it and make it bigger.
These relay boards were designed to operate the relay when the input voltage at "IN" went to ground or zero volts. We are going all the way to -5 volts, so I put in the resistor. And the extra diode would help there too.
Good point Chuck, it is negative active, I'm thinking backwards. I'd just use the resistor.
Gentlemen,
Success.... See pics
Chuck you were right on with your diagram... I did not place any resistors on the yellow line (2.2K OHM). I thought I would see what would happen.
1. The switch works fine through the Legacy Remote. Solid switch movement... no issues.
2. I used one wall wart 5V.
3. I used accessory power, not track power for testing reasons. My meter showed 10.2 volts coming into the switch from my auxillary transformer (not sure if I used track power of 16V if all would work so smoothly).
4. Its not pretty looking right now... but your help Chuck and John made it happen and I thank you. Once I get it on my layout, I will advise on any mishaps, and may consult you.
5. Need to place correct color code wiring and heat shrink to pretty it all up.
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Great! 
Just a diode on the yellow line. No resistors.... Just a thought of precaution, should I add a resistor, or don't mess with success?
Super. I was concerned that the input circuit of the relay board would load down the RSC output or maybe it would over stress the opto input. Looks like neither. So great. I like the way the Fastrack switches work. Easy to do special apps with the RSC output.
Originally Posted by USCGRET:
Just a diode on the yellow line. No resistors.... Just a thought of precaution, should I add a resistor, or don't mess with success?
If I were sending it to the moon, I'd do it with a resistor. The diode actually helps drop the voltage a bit though, and it's fine as is.
