Introduction

Making your own radio frequency transmitter and receiver circuit is a very exciting thing. Here we will discuss the technology behind it and its practical use. We are trying here to make a remote controlled robot vehicle by using the transmitter and receiver circuit successfully. Creating a RF transmitter and receiver pair using inductors is a complicated process for a beginner. To avoid this difficulty modern technology has helped us by preparing readymade and easily available RF transmitter and receiver pair. It is easy to use and very effective. Here we are going to use 434 MHz RF transmitter and receiver module. This circuit we are going to make here will be versatile and you can use it anywhere according to your creativity. There is nothing to do with coding or using a microcontroller here. We will make our work easier by taking the help of encoder and decoder circuits. This circuit enables you to control four individual electrical or electronic devices from any corner of your house remotely using a single tiny remote control hand set.

The main parts we will need here are:

1. 434 MHz transmitter and receiver module.
2. HT12D
3. HT12E
4. 4017
5. 7805
6. BC547
7. Ice cube relay
8. Capacitors
9. Resistors
10. LED
11. Reset switch

Description of components

434 MHz transmitter and receiver module.

This is an PLL based ASK Hybrid 434 MHz RF transmitter and receiver module. It is ideal for short-range wireless control applications where quality is a primary concern. The transmitter module uses a SAW-stabilized oscillator, ensuring accurate frequency control for best range performance. The transmitter power supply ranges from a 3-12V, making it ideal for battery-powered applications. Here we will supply 5 volt. The receiver module requires no external RF components except for an antenna. The super-regenerative design exhibits exceptional sensitivity at a very cheap cost.

HT12D

We can get 8 address bits and 4 data bits by using it. It is a decoder integrated circuit that belongs to 2¹² series of decoders. This series of decoders are mainly used for remote control system applications. Generally it is used in interfacing RF and infrared circuits. By using the HT12D decoder, we can transmit 12 bits of parallel data serially. HT12D converts serial data to its input to 12 bit parallel data. These 12 bit parallel data is divided in to 8 address bits and 4 data bits.

HT12E

HT12E is an encoder integrated circuit of 2¹² series of encoders. They are paired with 2¹² series of decoders for use in remote control system applications. It is mainly used in interfacing RF and infrared circuits. It encodes the 12 bit parallel data into serial for transmission through an RF transmitter. These 12 bits are divided into 8 address bits and 4 data bits. HT12E has a transmission enable pin which is active low.

Power supply for the circuit

To get 5 volt supply from 12 volt battery we are using a 7805 voltage regulator IC. A 0.1 µF mica capacitor is used across the final output to get better stability.

How to test the encoder and decoder

The above schematic is used to test the HT12E and HT12D. The relation between encoder and decoder is established by connecting a wire between pin number 17 of HT12E to pin number 14 of HT12D. At first all the four LEDs are on when the circuit is given power. When you press the push button corresponding to pin 10 of HT12E then only the LED connected to pin 10 of HT12D becomes off but the rest three are glowing as before. In this way when you press the push button corresponding to pin 12 of HT12E then only the LED connected to pin 12 of HT12D becomes off but the rest three are glowing as before. This is how the encoder and decoder pair is tested.

Preparing the transmitter section

The RF transmitter section is prepared according to the upper schematic diagram. The 5 volt supply is derived by using a 7805 voltage regulator IC from a 9 volt battery. It will be better to use a 25-30 cm antenna.

Preparing the receiver section

The RF receiver section is prepared according to the upper schematic diagram. The outputs are taken from pin #10, #11, #12 and #13. As our main objective is to control four distinct devices through remote we will need four latch circuits. The trigger signal is collected directly from pin #10 for a latch circuit. In this way four distinct latch circuits get their trigger signals directly from pin #10, #11, #12 and #13 respectively.

Avoiding interference with your friends who are making the same project.

First thing is the address pin connection patterns of encoder and decoder should be identical for a student but it mustn’t match with any other students. If this happens your receiver will respond to your friend’s remote and vice versa. We have grounded all eight address pins here for both encoders and decoders. You can select any combinations of   address pins to be grounded.

Preparing the latch circuit using 4017 IC

Here we are using a decade counter IC 4017, which counts or shifts the output for each rising edge of applied clock signal. It has 10 outputs. The outputs are obtained sequentially from pin #3 to pin #11. When there is a logic high pulse at pin #14, the output pins of the IC 4017 are switched high sequentially in the order: #3, #2, #4, #7, #10, #1, #5, #6, #9 and #11. But we are going to use only two outputs to switch ON and OFF by shifting the HIGH state between these two outputs. The alternate toggling at pin #14 is recognized as clock pulses and is converted into the required toggling at the output pins.

Working of the latch circuit

Ten outputs are obtained sequentially from output 0 to output 9 from the pins #3 to #11 in the order: #3, #2, #4, #7, #10, #1, #5, #6, #9 and #11 for every advancement in the clock pulse. However, this counting can be stopped at any instant and repeated by just connecting any of the above pins to the reset pin #15.

We are getting output from pin #3 which is output 0. We are interested only in output 0 and output 1. So, we have to connect pin #4 to pin #15. Because we don’t want rest of the outputs from output 3 to output 9. So, the counting will be circulated only between output 0 to output 1 that means in between pin #3 and pin #2.

Now the output for ON/OFF is taken from output 0 at pin #3. In the initial state output 0 is high and output 1 at pin #2 is in a low state. When we provide a trigger signal the counter gets a positive edge triggering at the clock input pin #14. Now the High state shifts from output 0 to output 1 and pin #2 will have a high state at the output. In this way we get a typical toggling action in between pin #3 to pin #2.

Every time a positive trigger is applied to the base of transistor T_1, it conducts and pulls down pin # 14 of the IC to ground. This brings the IC to a standby position. At the instant, the trigger is removed, T₁ stops conducting, pin #14 at that time receives a positive pulse through the 10kΩ resistor connected to the 5 volt supply. The IC considers this as a clock signal and quickly toggles its output from its initial pin #3 to pin #2. The next clock pulse produces the same action as a result the output shifts from pin #2 to pin #4. As pin #4 is connected to reset pin #15, the counting returns back to pin #3 (starting point). In this way the process is repeated every time T₁ receives a trigger either manually or through any external circuit.

The output current at pin #3 is very low that means in terms of milli amperes only. To use the latch circuit with heavier loads, we need a relay driver circuit. Here transistor T₂ with 10kΩ base resistance forms the relay driver circuit which drives an ice cube relay connected with external 12 volt supply to drive a 12 volt Dc motor.

The above schematic shows only one latch circuit. We have to prepare four of them.

Connecting the motors for RF car.

We have used here four 12 volt DC gear motors having 100 RPM each. The terminals of two motors are connected in such a way that if one acts as a generator then another acts as a motor. We have connected four motors one pair in left and other pair in right side of car in such a way that by driving only two motors from each pair we can advance the car in forward direction. Follow the latch schematic for supplying power to motor.

Operating the RF remote control car

We have used only two latch circuits here, taking two distinct trigger inputs from pin #10 and #11 of the decoder IC. Initially four motors rotate and car goes forward. Once pushing the button of remote connected to pin #10 of encoder, left motors stop as a result car turns right. Again pushing the button of remote connected to pin #11 of encoder, right motors stop as a result car comes to rest. To turn the car towards left, push the button of remote connected to pin #11 of encoder again.

Watch the Video in our You Tube Channel