In the initial state, the transistor VT1 closed and open VT2. At this time, the left side of capacitor scheme C 5 is connected through a small on-resistance transistor VT2 bus +5 V supply at this time through the ammeter PA1 is not. When the first negative half cycle of alternating voltage applied to the input of the tachometer, the transistor VT1 opens and closes VT2. At this time, the C5 quickly charged through the ammeter PA1, VD3 and R5. With positive half cycle of the input voltage VT1 closes and opens VT2. Now C5 discharges through low-resistance VT2 and VD4. The next negative half cycle process is repeated. Trimmer R6 set the upper limit of the frequency of the signal. Par C5 is selected depending on the type of engine. The higher the engine speed, the smaller the capacitor C5. Properly collected scheme does not require adjustment. It should only trimmer R6 set maximum RPM readings, opening the throttle motor to the end. Wiring Tachometer for electrical motorcycle is shown in Figure 2.
If the ignition pin, tachometer input is connected to point A. For contactless ignition -to point B.