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An Arduino tachometer for your older vehicle

Arduino TeamNovember 28th, 2016

Unlike most cars today, deepsyx’s old Opel Astra did not have a tachometer. So what’s a Maker to do? Build your own, of course.

To accomplish this, deepsyx used an Arduino Uno along with a few LEDs. The first LED turns on at 4000 RPM, while the others light up with every 500 RPM increment. At 5800 RPM, however, all the LEDs flash as a warning. There’s even a serial output of the RPM value, so logging real-time data can be a possible enhancement down the road.

I started by cutting a 5cm x 1.5cm piece of an old credit cart, drilled 4 holes in it, painted it black and glued 4 LED diodes to it. Then I soldered 220ohm resistors to each positive LED pin and used a common ground. I connected them to an Arduino via 5 x 30cm jumpers and hid the Arduino in a hole under the wheel. I connected the Arduino data pin via voltage divider to the signal pin of the coil and used an old phone charger to power the Arduino. In order to work, I shared the phone charger and Arduino’s grounds.

Intrigued? You can read more about this project on deepsyx’sGitHub page and over on Hackaday.



2 Responses to “An Arduino tachometer for your older vehicle”

  1. DocStein99 Says:

    I looked at the circuit diagram to capture the tachometer signal. It’s a little risky using a resistor direct to the board, from the car ignition signal – but I guess it got the job done.

    If you wanted to consider some protection, you may want to try using opto-isolation circuits (such as a 817c) between the projects and outside signals.

  2. JoeNova Says:

    Your code doesn’t seem to work. I’ve followed everything exactly.

    I noticed that you declare the Input pin for the tach signal, but its not used anywhere else in your code. I’m not sure exactly how you’re supposed to calculate the RPM when you ignore the input.

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