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How remote controls work

How they work


The emission spectrum of a typical sound system remote control is in the near infrared. The infrared diode modulates at a speed corresponding to a particular function. When seen through a video camera, the diode appears to illuminate purple light.Most control remotes for electronic appliances use a near infrared diode to emit a beam of light that reaches the device. A 940 nm wavelength LED is typical. This infrared light is invisible to the human eye, but picked up by sensors on the receiving device. Video cameras see the diode as if it produces visible purple light.

With a single channel (single-function, one-button) remote control the presence of a carrier signal can be used to trigger a function. For multi-channel (normal multi-function) remote controls more sophisticated procedures are necessary: one consists of modulating the carrier with signals of different frequency. After the demodulation of the received signal, the appropriate frequency filters are applied to separate the respective signals. Nowadays digital procedures are more commonly used. One can often hear the signals being modulated on the infrared carrier by operating a remote control in very close proximity to an AM radio not tuned to a station.

Standby power

To be turned on by a wireless remote, the controlled appliance must always be partly on, consuming standby power. Studies indicate that around 5-10% of domestic electricity is consumed by appliances when they are off. In the average home, 75% of the electricity used to power home electronics is consumed while the products are turned off.