Infrared circuits

Infrared circuits work with infrared light, a band of electromagnetic radiation just beyond the red end of the visible spectrum that the human eye cannot see. Because infrared can be generated and detected with inexpensive semiconductor components, it is widely used to carry signals through the air over short distances. An infrared system pairs an emitter, usually an infrared light-emitting diode, with a detector such as a photodiode or phototransistor, and the circuit controls how light is sent and how the received light is turned back into an electrical signal.

The most familiar use is the remote control, where pressing a button causes the emitter to send a coded series of infrared pulses that the appliance's receiver decodes into a command. To distinguish these signals from background light and heat, the infrared is usually switched on and off rapidly at a fixed modulation frequency, and the receiver responds only to that frequency. This modulation, combined with coding, lets several commands and even several devices share the same medium without confusion.

Beyond remote controls, infrared circuits are used for proximity and object detection, where reflected light reveals the presence of a nearby surface, and for short-range data links between devices. Other applications include safety beams that detect when something crosses a path and simple optical communication links. Collections of infrared circuits include transmitters, receivers, detectors and remote-control projects, illustrating how emitters and sensors are combined with modulation to send information using invisible light.

Frequently asked questions

What is infrared light?

Electromagnetic radiation just beyond the visible red end of the spectrum, invisible to the eye but easily generated and detected electronically.

How does a remote control use infrared?

It sends a coded series of infrared pulses from an emitter that the appliance's receiver decodes into a command.

Why is infrared often modulated?

Switching it on and off at a fixed frequency lets receivers distinguish the signal from background light and heat.