Photo-Counter

Raju R. Baddi

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You can use this gadget to detect whether somebody opened your cupboard or drawer in your absence. The gadget is small and highly power-efficient. The small size means it can be easily camouflaged within boxes or containers of suitable size. The gadget is powered by a re-chargeable 4.5V NiCd battery, which can be used again and again. The quiescent power consumption is extremely small, so the gadget remains active for several days with a single charge.

Fig. 1: Photo-counter circuit
Fig. 1: Photo-counter circuit

Fig. 1 shows the circuit of the photo-counter. Working of the circuit is simple. When light falling on the photodiode is interrupted, counter CD4040 advances by one and the binary output is shown on the LED display. For example, if light falling on the photodiode is interrupted three times, LED1 and LED2 glow to indicate three counts.

Please note that only two output connections (LED1 for LSB and LED12 for MSB) are shown in the circuit. Others are indicated through dotted lines but are not shown here. You can connect the remaining outputs of IC1 with other LEDs (LED2 through LED11, not shown here) for appropriate counting.

Fig. 2: Author’s prototype
Fig. 2: Author’s prototype
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After assembling the circuit on a compact circuit board and giving it necessary camouflage, charge the battery once. Put the unit inside a cupboard or drawer, close the same and open it. You will find that the reading of the counter has incremented by ‘1’ and can be read in binary fashion through LEDs. The reset button is used to reset the counter. The prototype in Fig. 2 shows the size of the gadget without LEDs.

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EFY note. Try using a separate power source to power the reading LEDs.


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