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Posted by on Dec 20, 2012 in Electronics, Robotics | 183 comments

Making an RF Car

Making an RF Car

RF controlled bot

This is an article written by a one of my readers, Yash Tambi, Core Committee Member, roboVITics. Do read this post and pitch in your comments below regarding this. Thanks!

Now a days, we see many remote controlled cars and robots, but, ever thought of making one?

RF controlled bots are the most simple of their kind. All you need are a few ICs, which are easily available in the market, a 433Mhz Transmitter and Receiver module, and the usual wires, resistors etc. Theoretical information related to this can be found in this post, where Mayank discussed about RF module interfacing.

Items required for making an RF car

Items required for making an RF car

The ICs we will be using are

  • LM7805 as voltage regulator
  • HT12D, HT12E for wireless control
  • L293D for driving motors

Before making the circuit permanent, it is always better to make it on a solder less breadboard and check for any rectifications in the circuit if needed.

Using the 7805 – 5V Voltage Regulator

Using the LM7805 IC is quite simple. It is used to convert the input varying supply (usually 9-18 volts) to a stabilized 5 volts supply, which is used to drive the circuitry.

LM7805 Pins

LM7805 Pins

Using the L293D – Motor Driver IC

We start with the L293D. L293D is a popular motor driving IC. It is a 16 pin IC. The IC has 8 pins on both the sides. It has 2 enable pins, 1 VSS pin, 1 VS pin, 4 ground pins, 4 input pins and 4 output pins. Though not required here, but in case you wish to learn how to interface L293D with a microcontroller, you could refer to this post by Mayank.

Following is the pin diagram of L293D –

L293D Pin Configuration

L293D Pin Configuration

The descriptions of the pins are as follows:

  1. Enable – the enable pins, when are given true, (i.e. 1) then they enable the respective part of the IC. The enable 1 chip enables the Left part of the IC for inputs and outputs, and so does the Enable 2 does to the right part of the IC.
  2. VSS – this pin is to be given an input of 5 volts. This is used to power up the chip for its operations.
  3. VS – this pin is given the voltage that we have to supply to the motors. This voltage comes out through the output pins. Due to the gates used in the IC, the output is usually 1.8 to 2 volts less than the Vs.
  4. Input – the input pin decides whether output has to be given to he respective output pin or not. When the Input is true, then output is also 1 in the respective output pin. When input in the Input pin is 0, and then output in the respective output pin is also 0.
  5. Output – the output pin is connected to the terminals of the motor. The input pins, as stated above, control its output.
  6. GND – these pins are the ground pins, or, in other words, Zero.

Note – When no input is given to the inputs pins (i.e. they are left floating) or 1 is given, there is an output from the output pins. Its only when 0 (ground) is given to the inputs, when the output is zero for the corresponding output pin.

The L293D IC can be used to control a maximum of 4 motors simultaneously. When 4 motors are connected to the IC, then for operation, -ve of each of the motors is connected to the GND, and the +ve terminal to the outputs. For bidirectional control, you can connect only two motors simultaneously as per the circuit diagram below:

L293D Based Motor Driver

L293D Based Motor Driver

This is how the circuit looks when soldered on a PCB —

L293D Motor Driver Circuit Soldered on PCB

L293D Motor Driver Circuit Soldered on PCB

Using the HT12D and HT12E for Wireless Control

HT12E Encoder

The next IC is HT12E. The HT12E is an encoder. It converts digital signals into suitable form to be transmitted through EM signals. It is an 8-bit Encoder. The HT12E is usually used for 433 MHz wireless modules. It is an 18 leg IC.

The pin configurations are as follows:

  1. HT12E Pin

    HT12E Pin

    A0: 7 – these are the address pins.

  2. GND – this is the ground pin. This pin should also be connected to the –ve of the battery.
  3. Vcc – the VCC pin is where we need to supply the input voltage for the working of the encoder. It is used to power the IC.
  4. Osc1: 2 – these pins are the oscillator input and output pins. For the ordinary circuit, they are connected to each other with the help of an external resistor.
  5. TE – this is the transmission enable pin. When this is given true, then data transmission starts.
  6. Output – this is an output pin. The data in EM signals is given out from this pin.
  7. AD0: 3 – these are the data/address pins.

Note – How does a transmitter know to which receiver it has to send the signal to? It depends on the configuration of the address pins on Both the ICs. For the Tx-Rx pair to work, they should have the same configuration of the address pins.

The address pins can either be grounded, or can be given Vcc individually. So the corresponding pins on the Tx and Rx have to have the same configuration.

You can also use a gamepad for the inputs. Remember, gamepads are designed to be active low in configuration i.e. when you press a key in the gamepad, it sends out ‘0’ and when left floating, it gives ‘1’.

HT12D Decoder

The next IC is HT12D. The HT12D is a decoder. It decodes signals into suitable form to be transmitted through EM signals. It is an 8-bit Encoder. The HT12D is usually used for 433 MHz wireless modules. It is an 18 leg IC.

HT12D Pin

HT12D Pin

The pin configurations are as follows:

  1. A0: 7 – these are the address pins.
  2. Vss – this is the ground pin. This pin should be connected to the –ve of the battery.
  3. VDD – the VCC pin is where we need to supply the input voltage for the working of the encoder. It is used to power the IC.
  4. Osc1: 2 – these pins are the oscillator input and output pins. For the ordinary circuit, they are connected to each other with the help of an external resistor.
  5. DIN – this is the Data input pin. The data input from the receiver module is fed in this pin.
  6. VT – this is an output pin. This pin gives the output as soon as any signal s received by the receiver.
  7. D8: 11 – these are the data pins.

Now a natural question arises… Why can’t we directly use the output pins from the decoder to run the motors instead of  using another IC?

Following are the reasons —

  1. Through L293d, we can give the desired voltage output to the motors.
  2. The output from the decoder has a very low current output, which is insufficient to drive the motors.

The output pins of the decoder are good only to be used as switches.

Note For coupling of two ICs, they have to be commonly grounded to the same source, otherwise they will not work.

Designing the Transmitter Circuit

  • As stated above, the address pins can be configured as per choice.
  • The Ground pin needs to be grounded.
  • The Vcc pin needs to be given regulated 5 Volts.
  • The output pin is connected to the data pin of the Tx module.
  • To enable transmission, the TE pin is grounded.
  • Resistors of 1.1MΩ are connected across Osc1 and Osc2 pins.
  • Pull-up resistors of 100KΩ are connected across D8, D9, D10, D11 pins. The other end of the resistors may be either grounded, or given 1, or left floating depending upon what we want as the default value from the output pins of HT12D.
  • Suppose we ground the resistors’ other ends, then, by default, all the output pins in the HT12D will receive 0, and similarly vice-versa.
  • Switches may be used in between the data pins and the resistors.

You can also refer to this circuit diagram —

RF Transmitter Section

RF Transmitter Section (Click to Enlarge)

Designing the Receiver Circuit

  • The address pins must be given the same configuration as of those given in the transmitter circuit.
  • The VSS pin is to be grounded. Similarly, a 5v regulated output should be given to the VDD pin.
  • The D8, D9, D10, D11 are the outputs corresponding to those in the transmitter circuit.
  • A resistance of 51KΩ should be applied across Osc1 and Osc2 pins.
  • The data output from the receiver module is to be connected to the DIN pin.
  • The VD pin gets ‘on’ whenever the receiver receives a signal. It may be left unconnected.

You can also refer to this circuit diagram —

RF Receiver Section

RF Receiver Section (Click to Enlarge)

Upon soldering on a PCB, the circuits look like this —

RF Receiver Circuit Soldered on PCB

RF Receiver Circuit Soldered on PCB

Tire and Motor Selection

Now coming to tire and motor selection. This is a very basic bot, and thus one can use any tire or motor of their choice! :)

And it’s done!

Photo

My finished bot looked like this!

Final RF Bot

Final RF Bot

Video

And that’s it for now! Any kind of queries and discussion, please leave a reply below and I will be more than happy to get back to you! :) You can also subscribe to maxEmbedded for more interesting articles!

Thank you.

Yash Tambi
yash@delta.robovitics.in

183 Comments

  1. i want to conferm pin 0to7 of decoder are conectted with -ve

    • Hi Govind,
      I feel that you are smart enough to figure that out from the circuit diagram. And FYI, it is ground and not negative. Ground refers to zero potential, not negative potential.

  2. hey
    i want to use motors with full load current more than 1.8 amps but the max output current capacity of L239D is 1.2 amps. so if i connect the motors then the ic will burn. so kindly suggest what to do.
    need urgent help.
    thank you.

    • Hello
      What you can do is to make a motor driver board using relays. They have a much higher current capacity (> 5 amps).
      Hope this helps.

  3. Hi,
    Using a different frequency doesn’t seem to make a difference. How can you say that they seem to be communicating?

  4. where to connect m1-a m1-b m2-a m2-b pins of l293d ic??

    • They should be connected to the D0-D3 pins of the receiver.

      • hi,
        what are those m1-a m1-b m2-a m2-b pins of l293d ic ?where to connect the motors control for direction any switch.

        • You have four wires and four pins. If you understand how the ICs work, you should be able to figure out yourself which connects to what. Or else, the simplest way is to go for hit and trail!

  5. Thank You
    Your circuit is working fine…
    just some interference issues, any solution for that?

    • Vivek,
      Try setting unique address for your device. Also try to make sure there’s no other device operating at the same frequency in its vicinity.

      • Tried changing the address, but of no use.
        It was a competition, another fellow made a circuit using a micro processor but using the same frequency(433mhz)
        Still my circuit interfered with his and his with mine.
        Any way of preventing other 433 mhz circuits from interfering with us??

        • Hello Vivek See, the biggest problem with 433 is that they interfere a lot. Thats not only due to address, but also because there are a lot of devices operating at and around this frequency. Another thing is, that another person that you are talking of, might not have even set an address for his device. What you can do is to increase you signal strength and use a lot of filters in your antenna to filter out all the unwanted frequencies so that at least they don’t interfere.

  6. i want to know that whar are block with circle. and what i use for remote. can i use dpdt switch. plz send me 8051 burner circuit

  7. hy yash
    you have said in a comment that m1-a,m2-a,m1-b,m2-b
    are the terminals of the motors,and in the schematic of L293D it is said to connect the (7,210,15)pin of the ic to m1-a,m1-b,m2-a,m2-b respectively.My doubt is if we connected the terminal of the motors to those pins what should be connected to pin (3,6,14,11),In the schematic it says connect it to the motors ..

    • Hey Abrarham,
      Here is how you should connect:
      Receiver --> (2,7,10,15)L293D(3,6,11,14) --> Motors

  8. hi
    can please provide a best way to stop the interfering two RF modules of same frequency;
    ok let me ask you one thing is there any chances of interfering two module frequency’s even if they have different addresess

    • Yes they might. It’s always preferable to use different frequencies, or some other encoding scheme.

  9. i tried the circuit on bread board at 9v. but it didn’t work. is that supply can burn my decoder and encoder ic.

    • Yogi, the HT12D/HT12E can safely be operated up to a maximum input voltage of 12 volts.

  10. hey
    circuit is working thanks for perfect guidance. making rc car was my childhood plan. and u showed me the path. thanks again

    • We’re glad that your dream came true! :)

  11. Hi there..is it possible to make 8 motor running ( not altogether )

    • Yes it is, depends upon how you do it!

      • Can u help me to make them circuit? Please.i am a beginner in this. What different component and value do I have to replace on the circuits above? I’d like to build a robot.i want to push my son to learn eletronic

        • What do you want to do exactly? You’ll need to describe it.

  12. Hi.i just wonder can I use baby monitors parts for this circuit? Let say oscillator ,resistors …….the baby monitor that I have is 9 volt trasm and 9 volt receiv.

    • I’m sorry, but what is a baby monitor.. never heard of it before..!

  13. i have built the circuit and its working but even if i stop transmitting, the motors continues to run and receiver stops responding to transmitter.
    dont know why its happening.
    Any solution? please help

    • Hi Abhi,

      That is because when you stop transmitting, the last transmitted value is held in the buffer register of the decoder on the receiver side, and hence the command corresponding to the last transmitted/received value continuously executes. Makes sense?

      Hope this helps!

  14. hey max cam we imply d circuit with a video game remote…i mean replacing dpdts with the remote

    • A remote emits IR signals. You’ll need an IR receiver and then write a program on your microcontroller to decode those signals.

  15. Hey Max, entering pin L239D 12V 8 is really necessary? 5V or may be throughout the circuit receptor? Thanks

    • Hey Lucas,
      12V is necessary to drive the DC motor. The DC motors used in this tutorial are rated for 12V. So 5V supply may not be sufficient to generate enough torque.

  16. I have read that ask rf module is susceptible to noise.If i replace the ASK rf module with the FSK rf module what changes do i have to make in the ciruit? Is it feasible to go with fsk modulation technique ?

    • If you replace the RF module, that’s all you have to do. The rest of the circuit should still remain the same.

  17. Hello sir
    There is countinous receiption it means led continuous to blink at the output even though switch is off or on at input side
    What should I check now

    • Hi Vivek!

      That is how it is supposed to work. All the output pins of the Decoder IC are internally pulled up. When you push one of the switches on the transmitting end, the corresponding LED will go off.

      Hope this helps!

  18. Hello Sir
    While checking continuity at receiver side I found there short line between antenna and ground at receiver module
    Is that correct

    • Nope. Antenna should not be shorted with anything!

    • In this kind of device, the antenna is connected to the ground through an inductor.
      At RF frequency, it is not shorted, but of course, when you probe with a DC voltmeter, it appears to be connected.

  19. Hello Sir
    Can I use1 mega ohm resistor for oscillator at transmitter
    And 47k ohm resistor for oscillator at receiver

    • Hi Vivek!

      You can find that out by looking up the Oscillator Frequency vs. Supply Voltage Chart on the datasheets of both the encoder and decoder pair.

      Hope this helps!

  20. Sir
    Can u tell me reason by which I get short line between antenna and ground
    And how can I solve this problem

    • Hi Vivek!

      We have never really checked the continuity between the ground and the antenna nodes. Maybe, you should try using the circuit to see if there is a problem. Until and unless you have hardwired the any two points in the circuit, there should not be a problem.

      Hope this helps!

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