This infrared object counter can be put at the entrance gate to keep track of how many people are coming in. For instance, it can be used at bus stops or train stations to keep track of how many people arrive each day or week. A pair of infrared transmitters and receivers and a simple, low-cost calculator are used to make the counter. It works even when there is regular light around. The farthest it can find something is about 10 meters. That means that the transmitter and the receiver can't be more than 10 meters apart (at the opposite pillars of the gate). There is no need for a focusing lens. With an 8-digit calculator, the counter can easily reach 99,999,999, and with a 10-digit calculator, it can reach 9,999,999,999. Fig. 1: Infrared Object Counter: Transmitter circuit The transmitter circuit (see Fig. 1) is powered by a 9V battery and has two infrared light-emitting diodes and an IC 555 wired as an astable multivibrator with a center frequency of about 38 kHz (LEDs). The 5V regulated power supply built around transformer X1, bridge rectifier with diodes D1 through D4, and regulator IC2 powers the receiver circuit (see

Fig. 2). It has a simple calculator, an IR receiver module (RX1), and an optocoupler (IC3). Circuit operation When switch S1 is in the "on" position, the transmitter circuit turns on and sends out a square wave at pin 3. The two infrared LEDs (IR LED1 and IR LED2) connected to its output send out modulated IR beams at the same frequency (38 kHz). The frequency of the oscillator can be changed with preset VR1. In the receiver circuit, the sensor is an IR receiver module TSOP1738, which is often used in color TVs to pick up the IR signals sent from the TV remote. When the IR beams from IR LED1 and IR LED2 hit the IR receiver module IR RX1 of the receiver circuit, pin 2 gets a low signal. This keeps transistor T1 in a state where it is not conducting. Fig. 2: Infrared Object Counter: Receiver-cum-counter circuit Now, if someone walks through the gate and breaks the IR beam, the IR receiver module sends a high output pulse to pin 3 of the modules. So, T1 conducts to turn on IC3, and its internal transistor shorts out the '=' key on the calculator to move the count up by one.

Any general-purpose PCB can be used to put together both the transmitter and the receiver. About one meter should be between the transmitter and the

receiver. To calibrate the calculator, press the S1 and S2 switches and then the "on" key. Now, press the "1" and "+" keys one after the other to get the number "1" on the calculator's screen. Then, put a piece of cardboard between the transmitter and the receiver to stop the IR rays twice. If the calculator counts "2," the counter is working correctly for that range. You can also use this method for higher ranges. If there's a problem, you can change VR1. To set up the system, turn off the transmitter, the receiver, and the calculator. Then, put the transmitter and the receiver on opposite pillars of the main entrance gate so that they face each other. Put the calculator where it's easy to read. Connect pins 4 and 5 of IC3 to the calculator's "=" key connections on the PCB. Now, press the S1 and S2 switches on the transmitter and receiver to turn them on. After that, turn on the calculator and press the "1" key and then the "+" key to set it up. Your counter is now ready to do its job.