CIRCUIT IDEAS ELECTRONICS FOR YOU JULY 2002 T his add-on circuit enables remote switching on/off of battery-operated toy cars with the help of a TV/ video remote control handset operating at 30–40 kHz. When the circuit is energised from a 6V battery, the decade counter CD4017 (IC2), which is configured as a toggle flip-flop, is immediately reset by the power-on-reset combination of capacitor C3 and resistor R6. LED1 connected to pin 3 (Q0) of IC2 via resistor R5 glows to indicate the standby con-dition. In standby condition, data output pin of the integrated infra-red receiver/demodulator (SFH505A or TSOP1738) is at a high level (about 5 volts) and tran-sistor T1 is ‘off’ (reverse biased). The monostable wired around IC1 is inactive in this condition. When any key on the remote control handset is depressed, the output of the IR receiver momen-tarily transits through low state and transistor T1 conducts. As a result, the monostable is triggered and a short pulse is applied to the clock
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