New simple tachometer circuit based on 555
As shown in the figure, the pulse signal V1 from the switch contact, which is proportional to the rotational speed, is differentiated and added to the trigger of the IC, so that the circuit generates a fixed-width pulse when the single-stability is generated, and different rotational speeds have a proportional pulse number. The pulse outputted by the one-shot circuit is integrated by the constant current source VT1 and C3 to obtain a voltage proportional to the rotational speed, so that the number of revolutions can be uniquely on the electric meter.
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