August 17
Somebody asked how we do occupancy detection. It’s easy--a 38K resistor on one wheelset of each car, attached with conductive epoxy. If you look carefully, you can see that the wheels on the far side of the car are insulated from the axle by a black plastic sleeve (the other wheel is pressed onto the axle and is in contact with it) so our resistor is installed so as to bridge the insulating sleeve. Thus there is conduction from wheel to wheel via the axle and the resistor.