MSgpio.com read only forums (Jan.15,2018)

I have a 67 camaro with the original mecanical speedometer.
The 4L80e I am installing does not have the provision for the cable.
I know that there are adapters from electronic to mecanocal but the price is high.
I was wondering if it is possible to run a stepper motor (as the IAC motor for MS2) to drive the cable and keep the original speedo. (the motor speed would be propostionnal to VSS.

Is it possible or is the idea crazy?

Guillaume

Guillaume,

A stepper isn't really what you need for this. Steppers require 2 outputs, and an H-bridge, and while they could be implemented on a GPIO board, it would be at the expense of other functions.

A DC motor might work. This would require a PWM signal from one of the outputs (presumably one of the spare outputs). This would be fairly easy to implement. It will likely require a table of PWM versus speed, because the speed likely won't be completely proportional to the PWM%. Perhaps a 10 element table of PWM versus speed with interpolation (sort of like the pressure control output, but not a 12x12 table). You'll want to do a bit of research on DC motors to see what you might be able to use for that.

Let me know what you need from the software and I will look further into it.

The other possibility is to use the speedo output to convert to an electronic speedo - this is how my car is.

The speedo output - PT4/PWM1/Amp31 - might make a better choice than one of the spare outputs, now that I think about it (since no-one would normally have both a mechanical and electronic speedo, of course). The PWM1 circuit can already handle at least an Amp or two.

Lance.

I was thinking about stepper motor because the speed could be controlled, to avoid the calibration of the DC motor.
Even if it is calibrated, I don't know if it would be very accurate on a 43 year speedometer: already with the cable there are variation depending on the outside temperature due to grease viscosity I guess.

I am looking for a standard eectronic to cable converter, depending on the price, I will decide if I try the DC motor driven with PWM or not.

thanks Lance

Guillaume