In the proposed circuit, each pulse of light or infrared radiation that hits the photodiode generates a pulse whose duration depends on the RC network connected at peaks 6 and 7 of the 555. This pulse is counted by the 4026 which directly excites an anode display common. The circuit is supplied with a voltage of 6 V. The sensitivity can be adjusted by connecting in series with the 10k resistor on pin 2 of the CI of a 1 M ohms trimpot. For greater directivity and sensitivity, the photodiode can be mounted on an opaque tube with a lens. The reader can also improve the circuit by increasing the number of digits, thus enabling counting to 99 or even 999.
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