TVs, DVDs players, stereos, ACs – all these components are operated using remote controls from a distance. These remote control devices utilize low frequency light that are invisible to our eyes to send out signals.
The device has got an internal circuit with a processor and a light emitting device. Based on the function that you press (say changing a channel or reducing the volume), the processor is activated. The light emitting device sends a corresponding signal to the photocell (light sensitive area) of your TV. The TV receives the signal and a processor decodes the signal and activates the function accordingly.
There are two types of remote control devices – IR (infrared) and RF (radio frequency) devices depending on the nature of the signal it uses. You must be familiar with the electromagnetic spectrum which consists of radio waves, microwaves, infrared, visible, ultraviolet, x ray and the gamma rays in the order of their increasing frequency. Those frequencies not in the visible range are invisible to our eyes. Any warm object emits infrared radiation. Human, animals, the earth, the sun, stars, galaxies all emit infra red light.
Like visible light, infrared light too has a range of wavelengths. Those close to the microwaves are ‘far infrared’ and those close to the visible light are ‘near infrared’. Far infrared rays are hot (thermal) while near infrared rays are not hot at all and hence cannot even be felt. These near infrared waves are the ones used by the TV remote controls.
Infra red devices send out signal in the form of pulses while RF sends out in the form of radio waves. The range of operation is less for the IR device compared to RF. IR device can only operate within a maximum range of 9 meters while RF operates within the range of 30 meters. Also IR functioning requires a clear line of sight with no obstacle between the device and the TV. It is not so in the case of RF devices. Radio waves can travel through obstacles. What are the major applications of remote controls?