Remote Control System Contents: Basic remote control system Electromechanical remote system Electronic remote control system Automatic frequency tuning (AFT) IR-based remote control system

Basic remote control system The transmitter has provision to generate three ultrasonic signals having frequencies 41.25 KHz, 37.75 KHz, and 43.25 KHz. The microphone picks up the radiated tone and converts it into an electrical signal. The broad-band (30 to 50 KHz) high gain (≈ 106) amplifier amplifies this signal and delivers it to an array of tuned circuits. Each tuned circuit is resonant to one of the three frequencies that can be radiated by the transmitter. The output of each circuit is coupled to the armature of a functional relay through a driver. Thus, depending on the function to be performed, the corresponding series tuned circuit develops a large voltage across its inductor.

Block diagram of electromechanical control system

Block diagram of electromechanical control system

Electronic control system The ‘memory module’ consists of a neon bulb (NE), a lowleakage capacitor C6 and a MOSFET Q1. The neon lamp acts as an open circuit unless the voltage across it reaches the ionizing potential. Similarly, the input impedance of the MOSFET, being of the order of 108 ohms, behaves almost like an open circuit. Thus any charge once stored in the memory capacitor C6 will stay on for a long time.

Automatic frequency tuning (AFT) The local oscillator frequency may change due to ambient temperature changes, component aging, power supply voltage fluctuations and so on If the local oscillator frequency becomes higher than the correct value, the picture IF, subcarrier IF and sound IF frequencies will also become higher by the same amount. This will result in poor picture quality. Similarly, if the local oscillator frequency becomes less than the desired value, color reproduction will become weak and only a black and white picture will be seen on the screen. Similar troubles can also result imperfections of the mechanical/ electronic system employed for channel selection.

Block diagram of an AFT circuit

AFC circuit

IR based remote control system An IR remote control works on a pretty simple principle.  There are two arts.  1. Transmitter which would like to send some information (Remote) 2. Receiver which would like to see that information (The TV) The transmitter, which is simply an LED which emits photons in the 750 nm frequency range (IR), can be turned on or off by on an electronic control circuit. The receiver, which is a photo diode or a photo-transistor detects this IR signal and converts it into an electrical impulse. There is a physical link between the Tx and RX. The communication method used in remotes is called as PCM. In this technique we essentially assign a Tx information to each sequence of bits. Here's a sample 3 bit sequence... S D

IR based remote control system There is a physical link between the Tx and RX. The communication method used in remotes is called as PCM. In this technique we essentially assign a Tx information to each sequence of bits. Here's a sample 3 bit sequence... Now say If one want to turn on the TV, he has to press a button on the remote, then the electronic circuitry turn the IR LED on in the '111' (ON ON ON) pattern. Which is just keeping it ON for say 3 ms. If any one press the switch to increase volume, the LED is turned OFF, ON, ON (011) each with a predefined delay. Now at the receiver this pattern is detected as a sequence of ONs and OFFs. Which can be made to trigger the control circuits for doing the action which the bit sequence implies. 000 - Turn Off TV 001 - Select Next Channel 010 - Select Prev Channel 011 - Select Volume Up 100 - Select Volume Down 101 - Select Brightness Up 110 - Select Brightness Down 111 - Turn ON TV