11 Apr 2012

How to Make a People Counter

This is a very useful circuit and has unimaginable applications. You could use this counter to know how many people enter a mall daily, or use it with a conveyor to count the number of objects made, or with a powerful LASER you could even count the number of vehicles passing at a certain point! Moreover, by replacing the calculator by a stop watch, you could make an accurate automatic stop watch.

Materials Required:
  • An ordinary calculator
  • A powerful LASER
  • 9v Battery
  • 9v Battery Connector
  • PCB
  • 5v DC Relay 
  • LDR (photocell)
  • NPN Transistor
  • 100K Variable Resistor
  • Diode
  • 2 Push Button Switches
  • 2 Toggle Switch
  • Box to keep the circuit compact
People Counter Circuit Diagram
Step by Step Guide:
  • Firstly, solder all the components on a circuit board as indicated in the circuit diagram above
  • Open up the calculator and identify the points for the 'on', '+', '1' buttons 
  • Solder push button switches to the 2 points of the '+' and '1' buttons and a toggle switch to the 'on' button  such that they can be easily accessed
  • Identify the '=' button and solder the relay output to it
  • Cut out openings in the box for the 4 switches coming from the calculator, the toggle switch that switches on and off the entire circuit, the calculator's LCD display, and, most importantly, the LDR
  • Fix the PCB, the calculator and the switches into the box
  • As you want the LDR to be sensitive to the LASER's light and not be affected by ambient light, you need to block all ambient light coming to the LDR and let only the LASER beam to hit the LDR. For this you can fix an opaque tube (e.g. the body of a pen) to the LDR

      Now that the receiver component is complete, you just have set up the system in the desired place. So if you want to know the number of people that enter somewhere, place this receiver box at the trunk level of a person on one side of the door and the LASER on the other side exactly at the same level. It is preferable that the LASER be powered by the mains power rather than a battery as a weak beam of light would not be efficient. 

      Once you have placed the transmitter and the receiver, switch on the circuit and the LASER, press the '+' switch, then the '1' switch. Cut the beam a couple of times and see if the counter detects it. If it doesn't, increase the resistance of the potentiometer until the calculator adds a '1' at the slightest rupture of the LASER beam. Great! you have made your LASER pleople counter, but how does it function?

Let's go through electrical the process:
  • While the LASER beam is falling on the LDR, the latter's resistance remains negligible and the 'base' and the 'emitter' pins of the transmitter are shorted. Thus the relay does not get power
  • While the beam is cut, the LDR's resistance shoots up and the 'base' gets power. The relay goes on.
  • As the coil is charged, it shorts its two output pins emulating that the '=' button gets pressed and a '+1' is added on the display
  • Everytime someone or something breaks the LASER beam, a '1' keeps getting added to your total and you have your DIY LASER People Counter!
This is a simple weekend project that has applications in every field. Use your imagination, finds undiscovered applications for this counter and do write them to me! 


Anonymous said...

Very interesting site.

Anonymous said...

How big is the people counter

Gallactronics said...

The people counter circuit could fit in a box which is a little bigger than your calculator.
On the other end of the door/passage there'll be a small LASER pointer.
That's all!

Anonymous said...

is it possible to get photo of the finished product looks like

Anonymous said...

When kight is blocked from the LDR, then the relay is activated. However, the activation is not clean and sharp. The relay counts several times in a split second. To avoid this "switch bounce" it may be necessary to send the relay signal through a 555 timer set in monostable mode with a duration of 0.25 seconds.

Jaymar Caba said...

I have a question, if the peole will exit, it will be a minus of the counter. ?

borogol said...


...then make another one and add it on other side like this...


gallactronics said...

Unfortunately, if people exit, the counter still increments.

For differentiating between people entering and exiting, you will need to add another LASER transmitter/receiver and some additional circuitry.

soumik sengupta said...

I just want to know the number of npn transistor.. There are different npn transistors of different number, available in the market.

soumik sengupta said...

I just want to know the number of npn transistor.. There are different npn transistors of different number, available in the market.

Pranav Agarwal said...

It's an NPN 2N3904.

Matthew Theakstone said...

Just wondering what laser is suggested? perhaps with examples?


Pranav Agarwal said...

Any cheap key chain laser pointer will do the job

Anonymous said...

Is there a way to create a counter that would trigger a gate when a certain number is reached? And could it be set to trigger at different numbers for different situations?

Pranav Agarwal said...

It should be possible with logic gates. An easier alternative would be to use a microcontroller such as the Arduino