Remote controlled DC Drive

Abstract:- in most of the industries for motion control AC motor or DC motor are used. To control the motion there is a need of either AC drive or DC drive. The basic functions of this drive is to give smooth start to motor change the direction, change the speed etc. Here I am demonstrating one such application of DC drive that will control speed and direction of a DC motor using standard TV remote control. All the standard TV remote controls works on RC5 protocol developed by philips. So here I am using one RC5 decoder chip ST3049 that will decode the codes of RC5 remote control and directly gives 6bit digital data. Controlling of DC motor is handled by micro controller 89C51 with help of dual H-Bridge chip L293D.

Note:- RC5 decoder chip ST3049 is available at www.sunrom.com. The details of this chip given here are taken from datasheet of ST3049.

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Before starting directly the explanation of application let us first understand what is RC5 code?

RC5 code: -

RC5 is most popular protocol used for IR remote control. It was developed by philips. Now it has become universal protocol and used in almost each and every remote control. Also care is taken that IR code is unique for electronics equipments and manufacturers.

IR transmitter transmits 14bit code. This IR code is repeated after certain interval. This 14 bit code can be divided into 4 parts.

1. Two start bits.

2. One Toggle bit.

3. Five address bits.

4. Six Command bits.

Start bits:- Initial two start bits are always ‘1'.

Toggle bit:- Toggle bit changes every time when new button is pressed. Now this is useful for volume control. For example if you long press mute or any number key button then this 14 bit code is transmitted multiple time but command is executed first time only. But this is not the case with volume/channel change button. For volume change long press is important feature. So receiver controller uses this toggle bit and decodes command.

Address and command bits:- Five Address bits are used for system address. There is unique address for each equipments. Similarly there are 64 commands.

Here is the figure given for the RC5 code frame.

Now let us see how ST3049 will decode this code. So now let us understand working and operation of RC5 decoder chip ST3049.

RC5 decoder ST3049: -

The above figure shows shows pin diagram of chip ST3049. Pin functions are as described in below table

Pin no	Pin name	Function
4	input	receives input form IR sensor
Vcc	positive bias	connected to +V
Gnd	Ground	connected to Ground
T0	toggle	This bit toggles each time a new key is pressed. That allows identifying between holding down a key and pressing a key twice or more.
CA	command ack	this pin goes low for 50ms as valid RC5 code is received and data is updated on D0-D5
X1-X2	external crystal input	connect 4 MHz crystal along with two 22pf capacitors with these pins
A0-A4	address inputs	5 bit address input.
D0-D4	data outputs	6 bit data output. when any key is pressed from remote control it will generate 6 bit data

so with very few extra components we can decode RC5 code with the help of this chip. Here is the circuit that will receive RC5 code and generate 6bit output.

RC5 decoder circuit:-

As shown in above figure we need IR sensor TSOP1738, 4 MHz crystal, 1 LED, 2 capacitors and a current limiting register.

Connection: - the output of IR sensor is directly connected with input pin of ST3049. A 4 MHz crystal along with two 22pf capacitors connected with X1 & X2. One LED is connected to CA pin as shown. All the address inputs are connected to ground to set an address for TV set 1. 6 bit data outputs A-F can be connected with microcontroller directly. CA pin is also taken out to generate an interrupt when ever data is available on D0-D5.

Operation: - IR sensor will detect 40KHz IR signal generated form any standard remote (either TV, VCR, CD player etc.) It demodulates it and gives the RC5 code to ST3049 chip. St3049 Verifies valid RC5 code and depending upon the key pressed from remote control it will latch  6bit data on D0-D5 and also gives low pulse on CA pin. Some of the data outputs for very popular keys on remote control are as given.

Key on Remote control	6 bit data output
0 - 9	000000 (0) - 001001(9)
stand by	010010(12)
mute	010011(13)
volume up	010110(16)
volume down	010111(17)

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