Club 80-90 Forums

Hi Guys,

The green wire running from the coil to the dash ...
For models with a tachometer i understand this is what the green wire is used for?
For models without, why do i still have the green wire running into my dash?
Is it just ran up regardless and only taken advantage of in models with a tachometer?

How does a tachometer interpret the signal from the green wire? Does a voltage drop each time a sparkplug is fired? In which case how does the tachometer know how many sparks is required to turn the engine once?

Regards

Rob

The tachometer measures the root mean square of the voltage output, my aftermarket tacho has a switch on the back 4,6,8 depending on the number of cylinders. So switch it on 4 and it calculates the rms for a four cyliner, I would imagine the factory spec is already set at this.

Dont know if the green wire is standard, if not maybe you have had a dash swap at some time and had a clock fitted in instead

NicBeeee wrote:The tachometer measures the root mean square of the voltage output

Ah, that's useful. So it's not counting pulses then. Do you know if there's a conversion chart/algorithm somewhere? Does the voltage spike (upwards) or dip (downwards) with each pulse, and if it spikes do you know how high it gets?

you said root,snigger,different meaning in Oz

If you have the late van the green wire to dash feeds the buzzer of doom as well as optional tacho
buzzer will only sound with low pressure and above 2000 rpm, it needs the green wire to know what your engine speed is.
green is switched neg of the coil, it gets switched to ground for each spark so can be counted, when open circuit voltage on green can be quite high so be careful.

scottbott wrote:you said root,snigger,different meaning in Oz

Had a friend called Lisa Root, she was most popular when visiting our antipodean cousins!

itchyfeet wrote: green is switched neg of the coil, it gets switched to ground for each spark so can be counted, when open circuit voltage on green can be quite high so be careful.

Thanks Itchy

I found this site which shows a zener diode in the green wire to limit this voltage to 5V. Bertie says that's what's required for an Arduino voltage sensor. The rest of the circuit diagram looks like it's perfect as the basis for an Arduino tachometer.

Sorry don't know enough to comment

worth a read...

https://club8090.co.uk/forum/viewtopic.p ... 2&start=15" onclick="window.open(this.href);return false;