diode series or array?

[carl0s]

Mechanical car speedos are usually driven by a rotating cable from the
gearbox, and are all mechanical.

Probably the simplest way to convert to digital would be to glue a pot
track on the instrument face, with a pot wiper on the needle. Run it
off a regulated 10v or whatever, and feed to a multimeter or voltmeter.
Bit crude, but youre going to have fun trying to do it other ways.

The analogue needles are definately electronic as I've had the dash out a
few times. The car is a 1994 Toyota Supra. I was imagining wiring this unit
in parallel with the pos and neg of the drive to the needle, if you see what
I mean. I realise it might screw the calibration a little as there is less
voltage driving the speedo but would this still not be possible?

 

[Jasen Betts]

["Followup-To:" header set to sci.electronics.basics.]

The analogue needles are definately electronic as I've had the dash out a
few times. The car is a 1994 Toyota Supra. I was imagining wiring this unit
in parallel with the pos and neg of the drive to the needle, if you see what
I mean. I realise it might screw the calibration a little as there is less
voltage driving the speedo but would this still not be possible?

it depends on how the needle is driven... if pulses fron the transmission
are use to clock a stepper motor like setup that drives conventional
speedo mechanism (or drives the needle directly) there will be no analogue
voltage available.

moving coil meters aren't suited to much over 90 degreees needle movement.
if you're seeing significantly more than that don't expect to find a
convenient voltage source behind the meter.

Bye.
Jasen