problem is turning on the relay
if you connect from the power supply to the twin t the twin t dosn't draw enough to turn on the relay (coil is 1600 ohms).
At least I couldn't get it to close.
going to try a few other options. like driving a transistor to close the relay or even lower voltage relays.
OK OK guys. We are now where we were two weeks ago. Ha!!!!!!!!
Angie those relays will be expensive clunkers. No No No. What you need is a 12 volt single pole single throw. i.e. a single set of contacts that are open when the coil is DE-energized. That means the signals will be green by default. Those relay contacts will never need to pass 10 Amps. A reed relay is the answer and is most cost effective. This type of relay is only a magnetic reed switch with the coils wrapped around it. The reed switch contacts will never have to deliver more than 500 milli amps (on your layout anyway) Search the net for "reed switch relays".
Now, while you guys have been playing I have stripped my first Twin-T and replaced the power transistors with 2N2222As. I then returned to my original design and added a booster transistor (inverter). This allows me to use TWO 1N5404s, back to back across the Twin-T transistors. The inverter is also a 2N2222A. This inverter is normally conducting and you can get a relay and use normally closed contacts. This inverter will pull in the relay when the track is clear and open the contacts. I did try that but was not satisfied as the wheel contacts with the rail is worst case conductivity and inherently noisy. So I fed the boosters output to a resistor/capacity delay and fed the output to the relay driver which consisted of another 2N2222A. (Hey! it's all I got in my junk box). The signal switching delay is about half a second.
The circuit is of course less sensitive but that is expected. My trigger is about 1.2K. I intend to play with the booster's collector resistor to optimise sensitivity. I will keep you posted. Please note I don't have any 3904s in my junk box. You can try and experiment. I think the results will be about the same. Right now the Twin-T transistor collectors meet at a 10K ohm resistor and wiggle between 0.7 volts and 0.1 volts. That is a half volt swing which is enough. The booster collector has a 4.7Kohm resistor and swings between 0.1 volts and 5 volts. That too is enough butI will experiment. Finally I drive an LED with resistor as a relay substitute as I dont have a 12 volt one in my box. That collector wiggles between 12 volts and about 3. Not quite full on but adequate.
So total components is as follows. 4 x 2N2222a transistors.
2 x 1N5404 diodes (2 or 3 amp ??)
1 x 0.1 Micro fard cap (35v working)
4 x resistors
1 x sig diode (to protect the driver xtr)
Over Xmas I will play some more.
Now about your existing circuit. The twin ts are only taking turns trying to short out the 1.4 volts across the four diodes. The voltage wiggle is only about 0.6 volts which is not enough to cut the driver transistor off. Hence the dim red and yellow. I suggest you put about 10K in the twin-T collector circuit and use the ouput from the collectors to drive a booster stage. then take the ouput of that and feed it to the transistor that provides current to the signal driver. This will add another stage to the circuit. Guess what! That's four transistors. This is 'dejavu all over again'
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I just have to optimize that post booster stage on my lash up. Stay tuned.
And Angie, please forget about those industrial clunkers. I'm going to check some British mail order companies.
Merry Xmas. Tomorrow is my last day teaching. It's "the best beer in the world" time.
P