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.