Tachometer as Fuel Gauge

When I installed my EVision, I removed my fuel gauge. I'm using a fixed gear ratio, so motor speed isn't particularly interesting. The EVision has an output to drive a fuel gauge, but it needs reprogramming to drive a tachometer. Victor suggested that I bypass the tachometer's circuit and drive the movement directly. This is made especially easy because the tachometer comes out of the instrument cluster on it's own, and the movement is connected to it's circuit board with wires. I simply reconnected the movement to the input of the rev counter circuit and connected the EVision to the existing plug. Unfortunately the EVision's driver wasn't powerful enough to drive the movement beyond 2000 rpm, so I added a small transistor to amplify the signal. Power for the amplifier was already available on the circuit board so this was easy.

One of the great things about an electric car is it can be totally silent when you're not moving. Unfortunately the PWM frequency is about 3kHz and while the tachometer makes a fairly bad speaker, it's quite audible. I'm going to soften the switching with some kind of capacitor, which will hopefully make it silent. I'm also planning to make a circuit to turn off my water pump when the car isn't moving.