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Driving 0-5V tacho w/ 0-12V Vipec tacho aux out


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Hi guys

Not super clued up with electronics. How do I drive a 0-5V square wave tacho w/ 0-12V square wave Vipec tacho aux out?

A quick Google search shows a couple of different circuits (e.g. voltage divider) that may do the job but I would like to hear Vipec's preferred method or from those who have successfully modded the signal in the past.

Cheers, Chris

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Similarly, the factory speedo signal is an intercept of the cable that runs from engine ECU to VSS. The engine ECU supplies 5V to the hall sensor VSS (via the aforementioned cable) and the ecu internally monitors when the 5V is grounded by the VSS. Therefore, I take it that the speedo runs off a 0-5V square wave signal.

I'm assuming the Vipec speedo aux out is 0-12V square wave signal? If so, does this signal need to be reduced to 0-5V? What is the best way of doing this?

(Car in question is a 6G74 engined Mirage w/ the tacho instrument cluster from a 1.8L engined Lancer. Wiring diagrams are being done ahead of time as the parts procurement process will take a while.)

Thanks again, Chris

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The ECU typically switches the ground only and relies on the tacho to have an internal pullup to the correct voltage.

So in this case you would need to add a external pullup to 5V.

This can be done in the loom by adding a 1K resistor between the AUX out and 5V out of the ECU. This will then give you a 0-5 signal.

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