As part of the TesLorean project (http://dmctalk.org/showthread.php?13316-The-TesLorean) I'm keeping the stock gauge cluster, but attempting to "re-program" the gauges to present useful information from the Tesla drive unit, cooling system, traction battery, etc. The cluster will be driven by a microcontroller.

The Tach gauge is proving tricky. It takes GND, 12v, and a signal that comes from the coil and runs to the RPM relay and the Idle Speed relay. I've been experimenting with different signals but no sure success just yet. What I'm looking for is a waveform or the electrical characteristics of the tach signal.

Thanks
Jeff

PS. Just in case you're wondering, the plan is to use the Tach to display the "Miles of Range Remaining" The TesLorean has a 21kWh battery and should get about a 70 mile range. Miles Remaining is guestimated from the battery state of charge, the drive unit power consumption, and recent driving habits (miles/kWh).