Building an RF remote control

The easiest solution would be to take a cheap wireless toy car take out its receiver module along with its remote and use them in your robot. The other way round is this to make your own RF remote .

We will be using ASK (Amplitude Shift Keying) based Tx/Rx (transmitter/receiver) pair operating at 433 MHz. The transmitter module accepts serial data at a maximum of XX baud rate. It can be directly interfaced with a microcontroller or can be used in remote control applications with the help of encoder/decoder ICs.

RF Receiver Transmitter Module

The encoder IC takes in parallel data which is to be transmitted, packages it into serial format and then transmits it with the help of the RF transmitter module. At the receiver end the decoder IC receives the signal via the RF receiver module, decodes the serial data and reproduces the original data in the parallel format.

 

RF communication flowchart

 

Now in order to control say a dc motor, we require 2 bits of information (switching it on/off) while we need 4 bits of information to control 2 motors. HT12E and HT12D are 4 channel encoder/decoder ICs directly compatible with the specified RF module. The schematic is as shown below.

 

RF transmitter

RF receiver

 

In order to drive motors, we would need to connect a suitable motor driver at the output of the decoder IC. The motor driver circuit can consist of a relay, transistorized H-Bridge or motor driver ICs like the L293D, L298 etc. 

The example above shows the receiver section using the HT-12D decoder IC for a 4-bit RF remote control system.  Similarly the transmitter and receiver module can also use the Holtek 8-bit HT-640/HT-648L remote control encoder/decoder combination for an 8-bit RF remote control system.

 

Driving a motor through NPN

Driving a motor using PNP

 

Here we have used a flyback protection diode to prevent the damage of the diode. The data output of the decoder ICs should be connected to base of transistor (as shown in the figure).

Tip: Also note that we can also use a Darlington pair ULN2803, as it will provide higher voltage and eliminate the need of flyback diode (as it has an internal diode for protection.

 

Download the datasheets of encoder/decoder -

 

 

  

Comments

Member since:
15 March 2009
Last activity:
7 years 41 weeks

How can the TX/RX pair can be directly interfaced through microcontroller (Atmega16)...

Member since:
15 March 2009
Last activity:
7 years 41 weeks

I think the output are latched until unless you cut off the power...

Member since:
21 February 2009
Last activity:
7 years 9 weeks

Yes it is possible to operate more than one input simultaneously and correct output will be assigned automatically. Yes the outputs are latched and they do not change until some new data is received.

 

Member since:
15 March 2009
Last activity:
7 years 41 weeks

Thanks for updating the circuit.. its fine assembly now.. and should work fine.

will it be possible to operate morethan one inputs simultaneously and have the corrrect outputs assigned. Are the outputs latched or momentary?

will it be possible to operate morethan one inputs simultaneously and have the corrrect outputs assigned. Are the outputs latched or momentary?

Member since:
21 February 2009
Last activity:
7 years 9 weeks

 

Oscillator frequency vs supply voltage HT12D

 

From the above graph of Oscillator frequency vs supply voltage for HT12D (decoder) the oscillator frequency corresponding to 5V supply and 47kohm resistance comes out to be approximately 160kHz.

 

Oscillator frequency vs supply voltage - HT12E

 

Similarly from the above Oscillator frequency vs supply voltage graph for HT12E (encoder) the oscillator frequency corresponding to 5V supply and 1Mohm resistance comes out to be approximately 3kHz.

 

For the RF remote control setup to work properly oscillator frequency of decoder should be approximately equal to 50 times that of oscillator frequency of encoder which is true in your case.

Hence you can use 1Mohm resistance for encoder and 47kohm resistance for decoder.

Member since:
28 April 2009
Last activity:
7 years 7 weeks

L293D has special inbuilt protection diodes unlike other versions

Member since:
28 April 2009
Last activity:
7 years 7 weeks

Power Rating ?? , I have not used the Holtek Encoder and Decoder IC's but what i see from the schematic is , that the resistors mentioned are for oscillators. And if it is meant for oscilators the you need to refer the data sheet to see the range of values which can be used. As for power rating,  0.25 watts are generally enough for such circuits. Just check datasheet for the range of values

I would like to build the same rf remote control, but instead of using 750kohm for encoder and 33kohm for decoder, I would like to use 1Mohm one for my encoder and 47kohm for my decoder.If both are correct, would you like to tell me what will be there power rating since both encoder and decoder are operated at 5 volt ?

Thank you.