This project is a simpler version of a circuit that’s in use every day around the world. If you’ve ever wondered how stores or airports are able to count how many people enter their buildings each day, this project will show you how it’s done.
|1||568-9431-5-ND||IC JK TYPE NEG TRG DUAL 16DIP|
|1||100KQBK-ND||RES 100K OHM 1/4W 5% AXIAL|
|2||4.7KQBK-ND||RES 4.7K OHM 1/4W 5% AXIAL|
|1||47KQBK-ND||RES 47K OHM 1/4W 5% AXIAL|
|2||2N5087RLRAGOSCT-ND||TRANS PNP GP 50MA 50V TO92|
|1||10KEBK-ND||RES 10K OHM 1/6W 5% AXIAL|
|1||22KQBK-ND||RES 22K OHM 1/4W 5% AXIAL|
|1||3310C-001-503L-ND||POT 50K OHM 9MM SQ RTANG PLAST|
|1||2.2KQBK-ND||RES 2.2K OHM 1/4W 5% AXIAL|
|1||296-1563-5-ND||IC QUAD 2-INPUT NAND GATE 14-DIP|
|4||P563-ND||LED RED DIFFUSED 3MM ROUND|
|1||470EBK-ND||RES 470 OHM 1/6W 5% AXIAL|
|1||1.0KQBK-ND||RES 1K OHM 1/4W 5% AXIAL|
|1||MPSW42RLRAGOSCT-ND||TRANS NPN SS 1W 300V TO92|
As you can see from the schematic, this project uses a divide by four counter circuit and line decoder. Each time the light falling on the CdS cell is interrupted, a clock signal is sent to the first J-K flip-flop. A different LED will light to represent the number of “interruptions” the circuit manages to count.
The 50k variable resistor will adjust the sensitivity of the circuit. This circuit doesn’t show the light source, which can be a flashlight. Since the circuit uses visible light, the room should be dark to allow it to work. Each time the light to the CdS is interrupted, the LEDs should turn on and off to indicate the count.
Many buildings have similar devices in their doorways for counting and security purposes. Therefore they would be using more sophisticated counting, display, and alerting systems, but the concept is the same.