Counters with directional detection are useful for counting of objects moving along a predefined path. These may find application as visitor counters and also for counting of objects in a given direction and ignoring those moving in the reverse direction. Here we present a simple circuit that counts the number of persons or the objects entering the premises ignoring those exiting or leaving it.
The counter section consists of three IR LEDs, three photodiode detectors. The movement of objects including the direction of their movement is detected by the arrangement of the IR LED and photodiode detector pairs. The photodiode of each pair is mounted opposite to its corresponding IR LED fall directly on the photodiode detector.
Photodiodes D1 and D2 in conjunction with comparators N1and N2 from two sequential interruption detectors. The two outputs of the comparators are normally low (at ground level). When any person or object interrupts the light path of the first IR LED-photodiode pair, the output of comparator N1 goes high during the interruption period to set D-type flip-flop IC2-A, making its Q output (pin13) high. The high output of IC2-Ais fed to data input pin 5 of the second D-type flip-flop (IC2-B) inside CD4013.
Now when the same person/object interrupts the second pair of IR LED2-photodiode D2 during its forward movement, the output of comparator N2 goes high for the duration of interruption. Output pin 7 of comparator N2 is connected to the clock input (pin3) of flip-flop IC2-B.so when comparator N2 outputs a pulse on detecting an object, it clocks the D-type flip-flop, transferring the high state f its data pin5 to Output (pin1), which is otherwise at low level.
This, in turn, makes the reset input (pin4) of IC NE555 (IC3) high to make it active. Now when the person/object moves further in forward direction, it interrupts the third interruption-detector pair formed by IR LED3 photodiode D3.
The arrangement of photodiode D3 and its 1-mega-ohm series resistor (R6) is reversed compared to the previous two photodiodes connections. Thus, when photodiode D3 is interrupted, the non-inverting input (pin 10) of comparator N3 goes low to make its output pin8 low and trigger the Monostable multivibrator built around IC3 (NE555) to output a positive-going pulse.The output pulse of IC3 is used to trigger decimal counter/display driver IC 4033 (IC4).
Another IC 4033 (IC5) is cascaded with IC 4 to get the maximum count of ‘99’. The count (pin 5) of IC4 is used to trigger IC5. Thus up to 99 persons/objects moving is forward direction so as to sequentially interrupt the three IR LED-photodiode pairs will cause the dual 7-segment display to show the corresponding count on the display.
- Highly sensitive
- Low cost and reliable circuit
- Directional counting
- Can count up to 99 digits
- Error free counting with Monostable triggering
- Battle filling industries
- Visitors counting
- Cinema theaters
- Shopping malls
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