revolution counter - with digital read-out

with digital read-out The circuit presented is not only a suitable replacement of an existing mechanical rev counter, but may also be fitted in cars that have not one. The counting and memorizing occur in IC2, which also arranges the multiplexing of the signals to the three-segment display. Suitable units of time are arranged by oscillator N3 whose frequency is set to 1/3 Hz by P1. NAND schmitt trigger N2 generates a short negative pulse at the leading edge of the oscillator pulses, that is once every three seconds. The content of the counter is then stored in the on-chip memory from where it will be provided to the display. Network C3/R7/D4 resets the counter at the leading edge of each LE pulse: a new counting cycle then starts. The number of revolutions is derived from the pulses generated by the contact breaker in the car. These pulses are first limited by zener diode D1 to 12 V and then used to set transistor T1 into conduction via D2 and R2. Network C2/R6 arranges a logic lo...