Adding LEDs to Turnouts

[Joseph Sroka-10.2.8]

I have an N-gauge train with some remote-controlled switch tracks,
"snap-switch" type.

This is an older style train, not the DCC type.

I would like to add red and green LEDs to the switch tracks. The switch
tracks are operated from the "accessories" terminals of a small power
supply which are nominally 17 V AC, (I measured it open-circuit at 17.7 V
AC).

The switch tracks are operated by pressing momentarily on a momentary SPDT
switch.

I'd like a simple way to hook up the LEDs either at the remote location or
at the SPDT switch. Since power to the switch track is applied only
momentarily, I suppose that some sort of latching mechanism is needed.

The 17 V AC is part of the complication, it seems.

For reference, the switch tracks are Atlas #'s 2580 and 2581; the power
supply is Model Rectifier Corp. Railine 370N.

The switch tracks are apparently solenoid powered.

The power for the tracks only is 15 V DC. I wouldn't want to power the
LEDs from that terminal pair because it turns off when the train is
stopped, and includes the speed control.

Anybody here ever do this stuff with this type of remote turnout?

My guesses are some sort of relay or solid state relay, but I have no idea
what the specific part number or circuit would be.

Thanks.

--- Joe

 

[OBones]

The switches I have are fitted with an extra SPDT on the other end that
selects one side depending on which end of the track is selected.
This is purely mechanical. Maybe you could fit something like this on
the moving part of the tracks, so that it pushes the inverter one way or
the other depending on which track is selected.
Then you can put whatever voltage in the inverter, it is not electricaly
connected to your solenoid.

 

[John Woodgate]

I read in sci.electronics.design that Joseph Sroka-10.2.8

I would like to add red and green LEDs to the switch tracks.

You mean 2-colour light signals?

The switch tracks are operated from the "accessories" terminals of a
small power supply which are nominally 17 V AC, (I measured it
open-circuit at 17.7 V AC).

The switch tracks are operated by pressing momentarily on a momentary
SPDT switch.

I'd like a simple way to hook up the LEDs either at the remote location
or at the SPDT switch. Since power to the switch track is applied only
momentarily, I suppose that some sort of latching mechanism is needed.

Yes, you have the right idea, but it isn't a simple thing for you to do
if, as seems to be the case, you don't have much experience of
electronics.

You need to get an 'always-on' DC supply of around 5 V minimum,
preferably 12 V for easy LED-driving. Can you get at the 17 V AC supply?
It's probably used to produce the 15 V DC as well, so make sure that you
never have ANY connection between the two supplies. 17 V AC will give
you 24 V DC when rectified, so you will need to halve it with a
potential divider (two 1 kohm 0.5 W resistors). You don't need much
current, so an unregulated 12 V supply with significant internal
impedance should be OK.

Alternatively, just get a cheap 12 V DC regulated wall-wart. Regulated,
in this case, because an unregulated one will give you around 16 V DC on
light load, and that is too much.

You can use 4000 series or 74HC series logic chips to do what you want.
You need flip-flops to 'latch' the LED drive signals. The tricky thing
may be how to get the signals you need to tell the flip-flops to change
state. You could take a sniff off the momentary solenoid-drive signal,
but that's 'fail-dangerous' - if the flip-flops get out of step with the
solenoids, you'll get a green signal on the wrong track!