Slot Car Brake Lights

Some of my older Scalextric cars have working brake lights which come on when the car power is reduced (usually by it coming off the track)

I was curious to understand how this worked so that I could fit it to some other cars, so I did some experiments to figure it out. This is what I found.

Red LED's are used for the brake lights. At first I thought they might be driven by the back emf from the car motor. Experiments quickly showed that there was not enough energy for a decent show. The energy had to be coming from somewhere else. It is actually done with capacitors.

The circuit is as follows;

When the car is driven capacitor C2 charges up via diodes D1 and D2. When drive is removed C2 discharges through the two LED brake lights and the headlights, via R1. C1 is there to remove "ripple" from the supply, which would otherwise cause the brake lights to flicker.

I have built a couple of these circuits and instaled them in Metro 6R4's and Porsche 911.