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Shonali55

Shonali55

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  • Remote controls use the 36 kHz (or around) to put out information. Infrared light emitted by IR Diodes is pulsated at 36 thousand times per second, when transmitting logic level "1" and silence for "0".To generate a 36kHz pulsating infrared is quite easy, more difficult is to receive and identify this frequency. Infrared receivers that contain the filters, decoding circuits and the output shaper, that delivers a square wave.
  • Quartz crystals are seldom used in such handsets. They are very fragile and tend to break easily when the handset is dropped. Ceramic resonators are much more suitable here, because they can withstand larger physical shocks. The fact that they are a little less accurate is not important. This ceramic crystal (XL1) for reference oscillator is connected between pins no. 2 and 3 of M58484. The crystal along with capacitors C1 and C2 decide the frequency of reference oscillator. The reference oscillator work when the key button is pressed. This help in prolonged battery life. The circuit is always connected with battery but stand by current is very low. When one 20 keys is of the key is pressed the ceramic oscillator on automatically. Inside IC m58484 12 to provide clock pulse frequency of 38 KHz divide the 455 KHz of frequency. Each transmitted pulse has 20 clock pulses so that pulse width is approximately 0.53 mS. The key matrix is attached to IC M58484 through 6 X 5 matrix. The six input pins are 9, 10, 11, 12, 13, 14.the five output pins are 4, 5, 6, 7, and 8. The input referred as I1, I2, I3, I4, I5 and I6. While scanner output referred as. When no key button pressed all the inputs I1, I2, I3, I4, I5 and I6 are high and all scanner outputs QA, QB, QC, QD and QE are low.
  • In this mode significant part of circuit is switched off. When ay key is pressed, the signal Q will give an instruction to key encoder in relation with key input. The rows and columns information from the key-board is encoded with 6-bit binary. Each bit of a word is either 0 or 1. The short duration pulse is recognize by receiver as binary-0, and long duration pulse as binary-1.thus the 6-bit word formed from the unevenly spaced bursts
  • Each time you press a button at the Philips remote control, it sends a train of 14 bits, 1.728ms per bit, the whole train is repeated every 130ms if you keep the button pressed Each bit is sliced in two halves. The left and right half has opposed levels. If the bit to be transmitted is one (1), its left side is zero while its right side is one.  If the bit to be transmitted is zero (0), its left side is one while the right side is zero.  It means that the second half of the bit is actually the same meaning of the bit to be transmitted, as you can see at the shaded blue right side of the bit as on, means bit transmitted = 1. If you want to measure the correct logic level directly from the Receiver Output, you should measure at the first half of the bit. The correct interpretation, is that it changes level exactly at the middle of bit time.  At the IR Receiver output a bit Zero changes level from Low to Up, while a bit One changes level from Up to Low. There are a minimum quantity of incoming 27µs pulses to the demodulator understand it is at the right frequency and then drop its output.  The quantity of pulses used at the Philips remotes are 32 pulses per each half of the bit, 64 pulses per bit.  So, a bit "0" to be transmitted it means 32 square pulses of  27µs each, then 32 x  27µs of silence.  The bit "1" is the opposite, 32 x 27µs of silence followed by  32 square pulses of  27µs.
  • When you press a key at the remote, it transmits the train of pulses, and Microprocessor will receive bit #1 first.  It will be sensed right after the middle of the bit when it changes from high to low level to means bit "1".  This is the first time that microprocessor will "see" the incoming IR signal. Those first  two bits are need not to be decoded , not even the CHK bit so those 3 bits are skipped and start to receive the ADDRESS bits. To do that, 2.75 bits time it skip , and at the middle of the right level of the first ADDRESS bit to be read (non inverted level). After waiting for 4.752 milliseconds and then start to read the next 11 bits spaced 1.728ms each.   The first 5 bits are Address and the next 6 bits are  Command, logic correct level, LOW = 0, HIGH = 1.
  • The led driver circuit played a major role in transmission of IR signal. A square wave of approximately 0.53 mS (milliseconds) injected at the base of a transistor, can drive an infrared LED to transmit this pulsating light wave.  Upon its presence, the commercial receiver will switch its output to high level (+5V). This Circuit includes transistors TR1 and TR2. TR1 drives the transistor TR2. When TR2 conducts large current flows through infrared LEDs D1 and D2. The LED D3 works as indicator. The emission causes transmission of IR wave towards the remote receiver. The use of two parallel connected diodes instead of one ensures that the radiated signal has an adequate power level. The LED driver circuit shown in fig. h.Both the transistors operated as electronic switch. In quiescent state TR1 is held cut off by resistor R1. No current flows through R6, since TR1 is not conducting. With TR1 and TR2 cut off, the IR diodes D1 and D2 are also not conducting and no signal flow. When viewer enters a command like volume- up or volume-down into the remote controller key board, a positive going pulse appears at pin no. 16 of IC M58484. This pulse drive transistor TR1 into saturated condition. The transistor TR1 drives the transistor TR2 into conduction. When transistor TR2 conducts it acts as short circuit. Large current of 1 ampere flows from the battery to the two diodes D1 and D2 for a very short period. This give rise to an intense burst of IR radiation from the transmitter. The sequence of events is repeated until the 20 pulse code word corresponding to the desire command is transmitted full.
  • The oscillator circuit with in m58485 operates at frequency 455 KHz. Its precise value determined by components connected to pin-12 and pin-13. This frequency is divided internally to provide clock pulses. It is this clock pulse whose mark-to-space ratio varied by the command word pulses and converted by integration circuit to equivalent dc voltages. This dc voltage then becomes controlling signals. The integration circuit for color control is R4033 and C4019, brightness control isR4032 and C4018 and volume control is R4031 and C4017
  • Until and unless the Neon-lamp doesn’t get its equalized voltage it acts as open circuit. Due to which the input Impedance of MOSFET is getting high and also act as open circuit as neon lamp is connected to its base. If any charge get deposited in capacitor then it retain for a long period of time.To use the deposited charge in capacitor and make memory circuit functional DC control voltage is used. This DC voltage is obtain from broad band amplifier. its operation can be easily understand by the circuit diagram given below.

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