[woodcote]

Too impatient to wait for the reverse direction module from Modelling Electronics, I have been playing with the basic single-channel relay board (eg this one at bitsbox) that I'll be using to trigger the module...

   

I use one of these to launch the cars on my HO drag strip and use a simple momentary push switch to complete the circuit and power the strip while I'm holding the button down. So would simply attaching a wire to each rail in the 1-inch dead section on my loop give me the circuit I needed to trigger the relay in the same way? As a car crossed the dead section it would complete the circuit (irrespective of any current created by the motor), acting in the same way as the momentary push switch. So I gave it a go...

   

The relay board is powered by a 5 volt phone charger plug via a USB to 2.1mm DC plug (available at bitsbox here). I will also be powering the reverse direction module with this 5v supply - it should all fit neatly in a small plastic box.. but at the moment it's a bit of a mess! The output has a circuit with a motor in it, so I am not just relying on the green LED on the board telling me it's all working, I look for the circuit to work too.

   

I soldered a 150-ohm resistor between the cable and the relay board input on each wire. I'd tested the maximum voltage I was getting through the bare cables when a powered car crossed the dead section. Not surprisingly, the more powerful the motor, the more volts generated. The most I got was 0.25 volts.

When I placed a car on the 1-inch dead section, the green light lit up and the motor sprung into life and kept going. Rolling the car over the dead section caused the green light and motor to work from the moment the leading edge of both braids were on the dead rails, to the moment the trailing edge lost contact. Perfect. Running the car normally (at 9.5 volts via the driver station), it all happened much quicker, but the green LED and motor came on every time. And I didn't blow up the relay board (the relay is separated from the input via an opto-coupler), which was a bonus.

So all ready to go with the reverse direction module... which arrived this afternoon