Simple infrared sensor

The simplest infrared sensor, which will report the presence of an obstacle, can be made using just one transistor. This homemade product does not have a practical application, but rather a theoretical one, demonstrating the operation of an infrared obstacle sensor. Of course, no one bothers us to make a practical application, say, when building simple robots.

Infrared obstacle sensor circuit

The operation of the circuit is very simple. Infrared Light-emitting diode emits infrared radiation in a spectrum invisible to the human eye. If an object appears in the path of radiation, the infrared rays begin to reflect from the object and return back to the side LED. An infrared photo element (IR photodiode) serves as a trap for these rays. When reflected rays hit it, its resistance decreases. As a result, the current in the base circuit of the transistor increases and the transistor opens. The transistor load is blue Light-emitting diode, which begins to glow. You can connect a buzzer to the output and hear a sound signal.
If there is no obstacle to the sensor, then the rays are not reflected and the transistor does not open.
You can take any transistor of the same structure, you can use the Soviet KT315 or KT3102.

Sensor assembly

The circuit is assembled using wall-mounted installation. No setup required - works right away. I power it from a 3.7 V battery.

Infrared sensors are used by robotic vacuum cleaners, various control systems; a regular printing printer must have a couple of these, or even more, etc.

Watch a video of the infrared sensor in action