3 aspect model RR signalling help plse

[MrDEB]

I found the higher the resistor across the track rails the lower the current to third transistor (detect switch)
this mod will save buying opticoupliers.

 

[MrDEB]

new mod works in simulation but then maybe it won't for real???
ONLY Angi can tell for sure

 

[angie1199]

Ok, so I got same as mine,

Loco Present
Greens off on both blocks, red on yellow on

No loco present
Greens on but red and yellow only dim.

This was, I hasten to add, after I blew two transistors when the loco wasn't on the rails properly so created a short.

 

[MrDEB]

did you connect as per my schematic?
if so I would like to know how much current the loco pulls. Perhaps my sim has the "TRACK RESISTOR" wrong value.
will sim with amp meter on all LEDs to see if I can get a dim LED.

 

[MrDEB]

I get ua or pa depending on "track RAIL" resistor (went from 10 ohm to 10k)
are the led resistors big enough? I have 500 on the TINA sim.
are you connecting 12v or higher? that would make a difference on the LEDs being dim.

 

[Raiway Pete]

LED's bias resistor just dims the green led, all the time, just dims slightly when loco is present.

Trying to keep away from expensive relays.

What I was thinking, using my logical brain, was to reduce the current/voltage (whatever) to the base of the transistor controlling the green led being on. If there's less current there to start with then surely there's less to beat to switch it off? Or is that too logical?

Might have a go at building the LM393 comparator based detector, I got some of those and it uses 2 power diodes as the bridge

Dear Angie,

That's what I meant about the bias resistor. Try increasing that with a temporary potentiometer in series with the resistor. Then read the resistance of the pot + the bias resistr just before the green goes out. Replace the pot and bias resistor with a resistor as close to the read value as you can. The "non absolute ground" from the opto-isolator might now be enough to tip the green into the off state.

P

 

[MrDEB]

I think Angi is trying out my solution of a second diode on the GREEN LED base.
It works in sim but for real?
see a few post back where I have a screen shot of simulation.

 

[angie1199]

As per your schematic here

https://www.electro-tech-online.com/attachments/correct2-png.36535/

Loco Present
Greens off on both blocks, red on yellow on

No loco present
Greens on but red and yellow only dim. Sharing current.

It's like the detect transistor (T9) is not shutting off completely.

 

[MrDEB]

well we got part of the problem solved I guess?
will comer up with another solution?

 

[angie1199]

Beginning to think a relay might be the easier way to go.

What about these? I have no idea what I'm looking for on datasheets

RS Online
492-907 https://www.electro-tech-online.com/custompdfs/2009/12/0900766b80b76b3c.pdf


RapidOnline
60-0310 **broken link removed**

 

[MrDEB]

that would be better than trying to get the right bias etc.
one slight problem I see is getting the current right so you don't fry a relay coil.
putting n same place as the opticouplier is doable but my concern is current draw based on the resistance across the RAILS.
how much do they want for the relays?

 

[angie1199]

the 60-0310 is 50p (25+)

the 492-907 is 46p (15+, less over 50)

Still don't really want to fry them.

Pete looks like we going your way. Simplest way to switch the relay, without it frying if/when a loco derails and causes short?

 

[MrDEB]

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.

 

[Raiway Pete]

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' .
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

 

[angie1199]

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).

I was thinking the 12V version, which draws 400 ohms. Is it not possible to turn the output voltage from the twin t to 12vdc?

 

[angie1199]

And Angie, please forget about those industrial clunkers. I'm going to check some British mail order companies.

Merry Xmas Pete. Not so sure reed switches are cheaper though. Cheapest I could find from two mail order firms is **broken link removed**

£1.02 if I get 25+

 

[MrDEB]

the link shows .82 and .89
where do you see 1.02?
you can work with the 5 or the 12v reed switches.

 

[angie1199]

Yep, I'm getting old, I think I might have misread the single 12v switch as 102 instead of 112.

Still put's cost up a lot compared to the two relays I saw, just wish I understood the formulae that go behind electronics.

 

[Raiway Pete]

Merry Xmas Pete. Not so sure reed switches are cheaper though. Cheapest I could find from two mail order firms is **broken link removed**

£1.02 if I get 25+

Good God! I know the pound and dollar are in the tank but my All Electronics store still has them for much less. Or maybe it'sbecause I use 24 volt relays and the higher the volts the higher the rebate

I optimized the circuit. Angie the reason the twin -T won't drive a relay directly is because although the Vcc voltage is +12 the Twin-T transistors in parallel (one common emitter and the other common base configuration) the voltage wiggle goes from 0 to about half a 0.7 at the collector. Just like the back to back diodes it goes from 0.7 (approx) when off. Bt when either one conducts it shorts the 0.7 volts to ground. That 0.7 volt swing really needs to be amplified by a booster stage. In your circuit where you are taking the output from an emitter base junction you need to up the collector resistor to provide the full 0.7 volt swing and then feed it to a booster transistor. Connect the base of the booster directly to the Twin-T collectors, the emitter to ground and the collector to a 4.7 K resistor. If you put a relay in the booster circuit the whole signalling system will work backwards (when block is clear red and yellows will be on). So you either get a SPDT relay with a normaly open and normaly closed contacts and use the NC part of the switch. So when the TWIN-T is not conducting the booster is and will pull the relay. The NC contacts will open and your signals will indicate green.

But some don't like an active relay to indicate clear. So another amplifier is used to invert the output of the booster. That way the relay is not conducting in the "clear block" state. What is nice about that is one can put in a debounce RC network to delay the switching action by half a second or summat so that the twin-t doesn't cause flicker. This is what I suggest you do.

BUT before you do that hook the base of your 'detect' driver transistor directly to the Twin-T collectors. (no base resistor) Also up the Twin-T collector resistor to 3.9K. Your signal driver should work backwards (red when clear)but it should work clean. ie no dim lights. Once you got that straight I suggest you add another inverter transistor and use that to drive you signals. If that works then goodbye relays.

Go fer it.

P

 

[Raiway Pete]

Merry Xmas Pete. Not so sure reed switches are cheaper though. Cheapest I could find from two mail order firms is **broken link removed**

£1.02 if I get 25+

There is a magnetic shielded 12 volt reed relay for 0.65 for 25. I'd look at that because you need 25.