Wireless Auto Tachometer

Anyone performing their own automobile tune-ups knows how important it is to know your engines speed. With this tachometer, you can measure your engines speed without any connections or annoying timing lights.

Schematic

PC board layout and parts placement

Parts:

Notes:

1. Calibrate the unit as follows:

1. Set up this circuit:



2. Turn on the Tach and allow a few minutes for temperature stabilization.

3. Set S2 to 4 cylinders and adjust R5 for a meter indication of 180 (1800 rpm).

4. Set S2 to 6 cylinders and adjust R6 for a meter indication of 120 (1200 rpm).

5. Set S2 to 8 cylinders and adjust R7 for a meter indication of 90 (900 rpm).

2. To use the Tach, turn it on and let it sit for one minute to allow for temperature stabilization. Extend the antenna, select the right number of cylinders and hold the unit over the engine. If the reading is erratic or the needle jumps around, move the antenna closer to the ignition coil or spark plug wires.

3. The unit draws power from the car battery. If it is connected backwards, it will not work, but it won't be damaged