The tape counter described gives a ten-step indication with the aid of two ICs and a seven-segment display. Its great advantage is that it can be connected to a recorder in a straightforward manner since it records the length of time the motor runs.
The motor of the cassette player is connected to the reset input of IC2 and to the circuit earth. It is necessary for the motor to run only when the tape runs: in two- and three-motor decks the capstan motor usually runs continuously. At the instant the reset input of IC2 goes high, the timer begins to deliver very-low-frequency pulses: one pulse every three minutes with S2 in position C60 as shown in the diagram, and one every 4 1/2 9 18V minutes in position C90.
The pulses are applied to decade counter/display driver IC1. This stage raises the display position by 1 for every pulse. so that at the end of a C60 or C90 cassette the display has gone through positions 0-9. The display is reset by pressing S1.
Owing to leakage currents and the tolerances of the electrolytic capacitors in the timing network. R3-R2-R3-C2 (or R3-R2-R1-C3), it may be necessary for the value of R2 to be changed (empirically).
Because the first cycle of a Type 555 timer is always longer than the next, repeated stopping and starting of the tape may result in an appreciable error in the displayed time.
It is essential that the input voltage is free of noise pulses to prevent the 555 being reset erroneously.
The counter draws a current of not more than 50 mA.