C U W 3 E DU

This simple circuit can be used to count the number of cars entering a parking lot. The circuit is built around comparator LM311 (IC1), timer 555 (IC2), 4-digit counter IC 74C926 (IC3), four LTS543 seven-segment displays (DIS1 through DIS4), four npn transistors BC548 (T1 through T4), a foot switch S2 and a few discrete components.

In place of the foot switch, you can also use a normally-open-type reed switch. Mount the reed switch on the gate along with a magnet such that when someone opens the gate, the switch closes momentarily to provide a clock pulse for IC3 from timer IC2. The foot switch or reed switch plays an impotant role in timer NE555 operation and hence counting of the cars, provided mains power switch S1 is ‘on.’

LED1 indicates that power to the circuit is switched on and the circuit ready to count. The circuit has a facility to check the battery voltage. At normal voltage (6V to 9V), LED2 remains off and LED1 glows. When the voltage goes below 4V, LED2 glows to indicate that the battery requires replacement or recharging.

Install the foot switch on the vehicle track at the entrance gate such that when any vehicle passes through the gate, the foot switch is pressed or pushed down momentarily by the wheel of the vehicle. This provides a trigger pulse to pin 2 of timer IC2, which is configured in monostable