Digital Motorcycle Tachometer.

Hey Everyone,

I want to build a digital tach for my '05 Yamaha R6. I've got the display side down, it's just the input signal I need confirmation on.

I've found that the OEM tachometer signal is a square wave, average peak voltage of 10v, but can be upto 14v at higher RPMs.

  • Can I just use a resistive voltage divider to get the signal down to the 5v level?
  • I was planning on just using a LM7805CT-ND to step the supply voltage down to 5v to power the Arudino.

Thanks! Kelvyn

Can I just use a resistive voltage divider to get the signal down to the 5v level? I was planning on just using a LM7805CT-ND to step the supply voltage down to 5v to power the Arudino.

  1. You would be better off with a 4.3v Zener diode in series with a resistor to have a safe voltage below 5.5v on the input of Arduino.
  2. You might need to step the voltage down twice depending on how much current you need. You might want to consider a switching power supply. Automotive power is noisy.

cyclegadget:

Can I just use a resistive voltage divider to get the signal down to the 5v level? I was planning on just using a LM7805CT-ND to step the supply voltage down to 5v to power the Arudino.

  1. You would be better off with a 4.3v Zener diode in series with a resistor to have a safe voltage below 5.5v on the input of Arduino.
  2. You might need to step the voltage down twice depending on how much current you need. You might want to consider a switching power supply. Automotive power is noisy.

I've not taken a class with Zener diodes yet, how would that circuit look?

I don't need much current, and as long as the noisy power won't harm the arduino, it should suffice for now.

At the bottom of this page is the circuit I am describing. They used a 5volt zener in the diagram although a 4.3v zener might be a bit safer.

http://www.8051projects.net/lofiversion/t16450/atmega16-2x16-lcd-to-design-multimeter.html