Hello chaps, just been trying to find a tacho driver wiring schematic to convert the standard 20v AGU signal into a standard mk2 clocks signal. I know you can buy these off the shelf but I would rather build it myself. Cheers Neil
I'm using an OE AGU ecu runing 3 pin coils. I've scoped the signal and its not what I expected. Is a 12v signal but only drops to 10v instead of dropping to 0v. I have saved the signal on my scope so I can up load it if needed.
Not really an option for me, I'm running one of these bad boys... I've got it running though a CAN interface at the moment because it doesn't understand the OEM signal for rpm. It works but the rpm display is too slow to keep up with the actual rpm.
Well, might not be helpfull, but.. http://www.youtube.com/hidromail#p/u/34/g2hgrHivXIU We connected directly from the PIN 6 from the ECU to the cluster. Just a wild guess here, as I don't know STACK or similar.
Liking the videos mate. Was that mk1 a diesel? How much smoke!! I can't remember off the top of my head the pin layout on the ecu but i'll have a look today and see whats what. As long as it's a 12v square signal it will work. I may have to use an injector or coil trigger but I didn't really want to do this as I've got the wirring there and just needs a tacho driver to make it work.
Yeah, that orange mk1 is a Diesel PD150. That cluster you have, has a digital input, right? If so, I would assume it's like the Corrado one. So, the information provided by the ECU should be OK for you. PS- I mentioned the VSS, but I don't know what I was thinking at the time. VSS is for the speedo... So, just check pin 6 from the ECU, and you should see the voltage. Maybe Autodata can help you on this?
Double checked the wiring today and as I thought, I am already using pin 6 but the signal is no good for the cluster. This was the reason for trying to build a tacho driver for mk2 clocks as the cluster would be able to understand the old school signal. Failing that I'll have to run another wire to the cyl. 1 coil trigger at the ecu (yet to check signal but should work) Any ideas for the driver anyone?
could you not do a similar thing see link good info in there http://www.clubgti.com/forum/showthread.php?t=214566
Cheers Ben, that is some good info but I dont think it will work as I only the one signal wire to play with for now. I might have to resort to cutting into the coil wires and trying the diode trick if all else fails though. This is the standard 20v tacho output from pin 6 and this is roughly what I need to convert it to (shown in red)... Got a rough idea I think will be easier if someone can point in the right direction tho
This is what I was thinking, not sure on the current, but I'll investigate. I've got an old set of A3 clocks that I've taken apart and I found the transistors on the board but have yet to trace the signal to determin which is which.
The part numbers on the transistors are BTS409L1 http://www.datasheetcatalog.org/datasheet/siemens/BTS409L1.pdf and BTS426L1 http://www.datasheetcatalog.org/datasheet/siemens/BTS426L1.pdf Yet to check the input output signals as I have no means of generating the tacho signal on the bench so I'll have to hot wire it to the car.
I now have a working rev counter! I cant belive how easy things are when you know the answer I stripped out the A3 clocks and hot wired them so I could run them on the car, checked the signal off pin 6 and it had now changed to the 12v sqare wave that I was after This could mean only one thing, that there was not enough load on the circuit to bring it to earth! After quickly scrapping the now ruined A3 clocks, I fitted a 13K ohm resistor in there place dropped it to earth and job done! Took all of about an hour to fix and fit it up nicely.
Cheers dude! With this new found electrical mastery I'm now working on converting the speedo signal. Is a sine wave at the moment and needs changing to a square wave Managed to rob some bits off the A3 clocks which should sort it out fairly easily I hope.
