List of DIY Electronics Engineering Projects

Simple Object/Visitors Counter Circuit using LDR

After a short time off, I am back with a simple object/visitor detecting and counting circuit, dedicated to  all electronics hobbiests. This project counts how many objects or persons passed through its field of visibility. In order to keep the circuit simple, it is implemented with a single digit seven segment display, so it can count only up to 9. It is also possible to extend the count by interfacing more seven segment display and its driver IC’s (CD4033). This simple electronics project mainly consists of two sections
   1. Transmitter Section
   2. Receiver Section

The Transmitter Section

It consists of only an ordinary LED and a 3V battery. By wiring it correctly the LED glows. Mount the battery inside a case, by protruding the led out of it. This will function as the transmitter. You can even use a laser, flash light or any other light source for longer range.

Circuit Diagram of Transmitter

Simple led connected to battery

The Receiver Section

The receiver mainly consists of an LDR(Light Dependent Resistor), CD4033 IC, a common cathode 7 segment display and a 6v battery to power the circuit.

Circuit Diagram of Simple Object Counter

Circuit Diagram

The Light Dependent Resistor (LDR) lowers its resistivity when light falls on it. This makes the NPN transistor (SL 100) to be forward biased. The voltage or current from the collector terminal is feed to the BCD to 7 segment counter IC, CD4033. This IC is capable of driving common cathode seven segment display. The count can be incremented by giving a positive voltage to its clock input or by any suitable electromagnetic radiation to its clock pin (Pin1).

Align the transmitter LED and Receiver LDR closely, keeping a space to pass the objects to be counted. Now, switch on the circuit, the 7 segment display may show zero initially if the wiring is made correctly. Just interrupt the direct falling of light from led to the ldr, by passing any suitable opaque objects in between the transmitter and receiver. Then you can see the counter increments and counting the number of objects passed!!


Author & Editor

I'm Tittu Thomas, An Electronics and Communication Engineer from India, Kerala. I love doing hobby electronics circuits, blogging, programming, etc. Started this blog while doing my B-Tech degree under CUSAT university.

5 comments so far:

  1. Sir pls tell me how to increase or decrease sensitivity of this circuit.

  2. Can anyone help me with power point presentation on this, please help me..

  3. Can I replace LDR to Photodiode? Im a newbie.

  4. Can I replace LDR to Photodiode? Im Newbie.


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