Digital speedo output

[BioniC187]

Hey guys,
I have the typical mechanical speedo in my car.
I want to be able to read my speed via the cable so i can send it to a micro controller. Has anyone done this before?
Maybe i should use an encoder and some sort of gear mechanism to run of the steel cable
Thanks

 

[picbits]

All depends on the car and the gearbox fitting for the existing cable.

On many older Vauxhall cars in the UK the cable drives a spinning disc in the speedometer which has an optical sensor to give the pulse.
Newer Vauxhall cars use one of the ABS sensors to provide the VSS signal

I've spent the day building amplifiers for ABS sensors to allow electronic VSS signals to be generated from cars without an existing electronic drive.

There are aftermarket sensors you can attach to many gearboxes but you'd have to see if yours is one of them.

 

[MikeMl]

If your car is so old that it has a spinning magnet inside the speedometer, then put a Hall Effect sensor inside the speedo case.

 

[envious]

or check into the old cruise control modules that used a cable and vacuum to control speed. it would give you excellent access to the cable and i belive most had gears inside, to where you could setup a magnet/pickup setup.

 

[BioniC187]

I'm gonna put a reed switch on the spinning magnet. The car instrument cluster is that old that it has that hehe

 

[picbits]

Don't use a reed switch, it will be too slow, you'll get switch bounce and potentially wear out fairly quickly.

Put a hall effect sensor on and get a nice clean square wave out. Heck - even painting the ends of the magnet white and using a reflective optical sensor would work fine.