VDO Tach drive - IRF540 PIP Circuit or Ignition spike only?

[roo]

Hi,

I have a 16V Corrado running MS2 with EDIS that i've recently finished. I've been doing some tuning this past week and the engine is running like a dream. My last problem is that I don't have my tachometer working.

As an alternative to using the two diodes connected to either side of the coil pack to generate the tach signal, I decided to use Jim's driver circuit that I stumbled across, based on the IRF-540 and triggered by the EDIS PIP signal.

Despite this circuit working, (i've checked it on the scope) it doesn't appear to be sufficient to drive my VDO tach. As the tach was originally fed from the single coil connected to the dizzy I can only assume that it requires the voltage spike generated from ignition, and so i'll have to use the two diode method.

Before I change over, can anyone confirm that these VDO gauges are only driveable this way, or has anyone had any luck driving them from the PIP output using Jim's circuit.

Cheers,
Andy

[The Witzl]

I've had problems running a VDO tacho from the low voltage ECU tacho output signal... it seems like the VDO gauge wants to measure the back-EMF spike from the negative terminal of the ignition coil.

If you already have the low voltage tach signal, you can build a "tacho booster"..... see this:

[turboy]

I believe that circuit was only to isolate the ignition signals. What you can do, and it is a bit of work, is modify your tacho. Usally al it takes is to bypass the high ohm resistor at the input. I've done this with my own tacho (golf II) and it works flawless. Use pin2 or pin11 from the edis module.

Simon

I have a 16V Corrado running MS2 with EDIS that i've recently finished. I've been doing some tuning this past week and the engine is running like a dream. My last problem is that I don't have my tachometer working.

As an alternative to using the two diodes connected to either side of the coil pack to generate the tach signal, I decided to use Jim's driver circuit that I stumbled across, based on the IRF-540 and triggered by the EDIS PIP signal.

Despite this circuit working, (i've checked it on the scope) it doesn't appear to be sufficient to drive my tach, which is made by VDO. As the tach was originally fed from the single coil connected to the dizzy I can only assume that it requires the voltage spike generated from ignition, and so i'll have to use the two diode method.

Before I change over, can anyone confirm that these VDO gauges are only driveable this way, or has anyone had any luck driving them from the PIP output using Jim's circuit.

Cheers,
Andy






__________ NOD32 2314 (20070606) Informatie __________

Dit bericht is gecontroleerd door het NOD32 Antivirus Systeem.
http://www.nod32.nl

[roo]

Excellent, thanks very much or the info!.

As the MK2 Golf clocks should be essentially the same as my Corrado ones, I think i'll have a try at modifying them and running them directly from EDIS.

[roo]

Just to close this off.

I attempted to modify the tachometer in the hope of enabling it to take the EDIS tach signal directly. However, after removing the tach from the instrument cluster, I realised that VW must have used pretty strong glue as I found it impossible to remove the needle and consequently couldn't get access to any of the circuit board to modify it.

So, unfortunately this method was a bit of a non-starter for me, on the plus side though the two diode method works perfectly with my tach!

[mk2_20v]

hey any idea if this will also work for gm dual tower coils? do you bypass the high ohm resistor and use the tach out on the ms?