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Wireless Auto Tachometer

2016-11-28 22:02  
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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

This is the schematic of the Tach

 

PC board layout and parts placement

This is the parts placement and printed circuit pattern of the Tach

 

Parts

Part
Total Qty.
Description
Substitutions
C110.47uF Capacitor 
C2147uF Electrolytic Capacitor 
D118V 1W Zener Diode 
D2, D3, D431N914 Diode 
M11200uA Meter 
Q1, Q222N3391A Transistor 
R1, R2, R931K 1/2 W Resistor 
R3147K 1/2 W Resistor 
R4110K 1/2 W Resistor 
R5, R6225K Trim Pot 
R7110K Trim Pot 
R81200 Ohm 2 W Resistor 
R10115K 1/2 W Resistor 
R1112.2K 1/2 W Resistor 
S11SPST Togglae Switch 
S21Three Position Single Pole Rotary Switch 
MISC1Telescoping Radio Antenna, Enclosure, Power Cable and Battery Connector 
 

 

Notes

Calibrate the unit as folows:
    Set up this circuit:

     

    This is the setup for calibrating the Tach

     

     

    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.
     

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