Wireless auto tachometer

INTRODUCTION
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.

Notes
Calibrate the unit as folows:
Set up this circuit:


Turn on the Tach and allow a few minutes for temperature stabilization.
Set S2 to 4 cylinders and adjust R5 for a meter indication of 180 (1800 rpm).
Set S2 to 6 cylinders and adjust R6 for a meter indication of 120 (1200 rpm).
Set S2 to 8 cylinders and adjust R7 for a meter indication of 90 (900 rpm).
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.
The unit draws power from the car battery. If it is connected backwards, it will not work, but it won't be damaged.

parts required

Part Total Qty. Description Substitutions
C1 1 0.47uF Capacitor

C2 1 47uF Electrolytic Capacitor

D1 1 8V 1W Zener Diode

D2, D3, D4 3 1N914 Diode

M1 1 200uA Meter

Q1, Q2 2 2N3391A Transistor

R1, R2, R9 3 1K 1/2 W Resistor

R3 1 47K 1/2 W Resistor

R4 1 10K 1/2 W Resistor

R5, R6 2 25K Trim Pot

R7 1 10K Trim Pot

R8 1 200 Ohm 2 W Resistor

R10 1 15K 1/2 W Resistor

R11 1 2.2K 1/2 W Resistor

S1 1 SPST Togglae Switch

S2 1 Three Position Single Pole Rotary Switch

MISC 1 Telescoping Radio Antenna, Enclosure, Power Cable and Battery Connector