I am trying to convert the mechanical speedo in my car to run from the vehicle speed sensor that's fitted to the gearbox. I need a method to covert the pulses from the sensor (0 to +5v) to drive a 12v motor that will drive the speedo.
I've calculated that the VSS outputs 7Hz at 10MPH linearly up to 87HZ at 120MPH.
From this, the speedo requires a rotational input from the motor of 167RPM at 10MPH, linearly up to 2000RPM at 120MPH
I've looked at frequency to voltage converters and frequency to PWM converters but am unsure of the best way to do this. Ideally the motor should be accurately controlled so was erring towards a PWM output.
Can someone point me in the right direction? A simple circuit with some adjustability so it can be calibrated.
Apologies if this is a little short on info, I'm a newbie at this!
Thanks in advance 🙂
Best Answer
A DC motor has a voltage rating and maximum RPM which is linear above some threshold to get it started due to stiction. It is linear when there is no load on the motor. However when mechanically loaded , current will rise and the RPM will drop so another speed sensor on the motor is necessary to keep it regulated while voltage must be increased a bit to generate power to match the mechanical power.