What Is a Remote Control ?
A Remote Control is a unit that receives optical signals from remote control transmitters used to control various devices in various situations, including AV equipment such as TVs.
Specifically, it receives optical signals from remote control transmitters, converts them into electrical signals, amplifies the signals, and converts them into digital signals. This signal is output and sent to a microcontroller or other device control device incorporated in a subsequent stage.
Uses of Remote Control
Remote controls are used in pairs with remote control transmitters and are widely used in home appliances and audio equipment. Typical examples of such applications are AV equipment such as TVs, Blu-ray and HDD recorders and players, audio equipment such as AV components, and home appliances such as air conditioners and lighting fixtures.
In the case of a typical TV, almost all functions of the device can be controlled by the remote control transmitter, such as power on/off, volume control, channel selection, input switching, menu display and selection, and so on. Therefore, these functions are converted from optical to electrical signals by the remote control in order to output signals from the transmitter to the microcontroller for control of the TV unit.
Principle of Remote Control
The principle of the remote control is that it receives modulated optical signals transmitted from the remote control transmitter and, after demodulation, converts the received optical signals into digital signals for output to transmit control signals to the microcontroller at a later stage.
The wavelength of the light emitted to the remote control receiver unit is usually near-infrared light of 940 nm or 960 nm. The remote control transmitter transmits the original signal modulated at 37.9 KHz to limit the signal ON period to a few percent in order to extend the battery life of the remote control. It is this modulated light that is received by the remote control.
The remote control receives the light at the light receiving element, amplifies this signal, demodulates the modulated wave at 37.9KHz, and outputs it as a digital signal of 3 to 6V. This is to match the operating voltage of the power supply voltage of the microcontroller, etc. connected in the subsequent stage. The microcontroller receiving the remote control signal analyzes the contents of the signal and controls the device according to the results.
There are several types of data formats used in remote control signals. All of these formats use similar light wavelengths and modulation frequencies, but they have different data structures so that they do not interfere with each other’s signals and cause malfunctions.
Characteristics of Remote Control
The items listed as features of a remote control often refer to a receiver circuit corresponding to Band I as specified by the EIAJ, but may also include one corresponding to Band III. The output of a photo diode that receives near-infrared modulated light sent from a remote control transmitter becomes a weak signal when it detects reflected light from a long distance or from a wall, but becomes a very large signal when operated from close range of the equipment.
Therefore, the amplification circuit that receives the signal is required to have a wide dynamic range of 80 dB or more, which is achieved by the built-in AGC. Since light emitted by lighting fixtures can have an adverse effect as noise, the photo diode is covered with a resin that has visible light cutoff characteristics (near-infrared light is transmitted) to eliminate the effect of lighting fixture light.
Furthermore, a bandpass filter with a steep pass-through characteristic is provided to avoid the influence of inverter fluorescent lamps, which blink at high frequencies. The output terminal of the remote control is typically an open collector to match the power supply voltage of the processor that receives the output signal, and a pull-up resistor is provided at the processor’s input terminal to receive the signal.
Other Information on Remote Control
1. Noise Suppression of Remote Control
If the environment in which the remote control is used contains noise sources (e.g., ambient light noise from inverter fluorescent lamps, power supply ripple, electromagnetic noise from power supply circuits, etc.), the remote control receiving distance may be shortened by such noise sources. Therefore, it is necessary to devise ways to avoid them.
While power supply ripple and noise contamination of the power supply circuit can be addressed in the circuit design, preventing the effects of fluorescent lamps requires structural innovations such as blocking light from the ceiling direction.
2. Precautions for Using Remote Control
The remote control has a very high gain, so it is sensitive to noise. Therefore, if the remote control has a shield case, it is important to connect it to the GND securely.
Most remote control modules are designed to be used indoors. When used outdoors, the current output of the photodiode becomes extremely large when sunlight shines on it, saturating the amplifier circuit that receives it and making it impossible to receive near-infrared light from the remote control transmitter.
Therefore, for equipment used outdoors (e.g., cameras and other photographic equipment), a remote control with specifications to prevent saturation by sunlight should be used.