Car Door Remote key sensor(Receiver And Transmitter)

RF Module Interfacing without Microcontrollers

Going wireless always starts with a basic RF communication, using serial encoders and decoders. This process and methodology is described here very aptly, doesn’t matter whether you are a newbie or not!

Going Wireless:

These days, the term wireless is very much hyped! Whenever we hear the term wireless, stuffs like Mobile telecommunication (GSM), Wi-Fi, Bluetooth,RF Communication, Wireless networks, Zigbee, I2C, SPI, DTMF, 802.11b,SimpliciTI etc etc etc. Well, fortunately or unfortunately, all of these protocols can be interfaced with a microcontroller in one way or the other. But what matters is the level of complexity.

To start off, for beginners, RF (Radio Frequency) Communication is the most preferred and low cost solution. All you need is a RF Module (Transmitter-Receiver Pair). Now, that’s not all. RF Communication works on the principle of Serial Communication. Thus, you need something which converts the conventional n-bit (4-bit, 8-bit, 16-bit, etc) data into serial data. For this, we have two choices:

• Use a microcontroller to convert the n-bit data into serial data and vice-versa
• Use serial encoders/decoders to do the same

Since the title of the post says that we shouldn’t use microcontrollers, the only option left for us is to use the encoder/decoder.

RF Communication Block Diagram:

A general RF communication block diagram is shown above. Since most of the encoders/decoders/microcontrollers are TTL compatible, most of the inputs by the user will be given in TTL logic level. Thus, this TTL input is to be converted into serial data input using an encoder or a microcontroller. This serial data can be directly read using the RF Transmitter, which then performs ASK (in some cases FSK) modulation on it and transmit the data through the antenna.

In the receiver side, the RF Receiver receives the modulated signal through the antenna, performs all kinds of processing, filtering, demodulation, etc and gives out a serial data. This serial data is then converted to a TTL level logic data, which is the same data that the user has input.

So now, let’s look into the hardware that are required.

RF Module:

RF Modules are used wireless transfer data. This makes them most suitable for remote control applications, as in where you need to control some machines or robots without getting in touch with them (may be due to various reasons like safety, etc). Now depending upon the type of application, the RF module is chosen. For short range wireless control applications, an ASK RF Transmitter-Receiver Module of frequency 315 MHz or 433 MHz is most suitable. They are quite compact and cheap! You can buy them from the following stores:

• Robokits
• Rhydolabz
• Sparkfun

A typical 315MHz (or) 433MHz ASK RF Module looks like this

PIN DESCRIPTION:

Features:

• Range in open space(Standard Conditions) : 100 Meters
• RX Receiver Frequency : 433 MHz
• RX Typical Sensitivity : 105 Dbm
• RX Supply Current : 3.5 mA
• RX IF Frequency : 1MHz
• Low Power Consumption
• Easy For Application
• RX Operating Voltage : 5V
• TX Frequency Range : 433.92 MHz
• TX Supply Voltage : 3V ~ 6V
• TX Out Put Power : 4 ~ 12 Dbm

This has single channel for data transfer, thus serial data communication is used.

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 , a 433Mhz Transmitter and Receiver module, and the usual wires, resistors etc. Theoretical information related to this can be found in this post, where Palak discussed about RF module interfacing.

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.

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 VSpin, 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 Palak.

Following is the pin diagram of L293D –

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:

HT12E Encoder: 

For Detail Click Here:Here

HT12D Decoder:

For Detail Click Here:Here

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 —

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 DINpin.
• The VD pin gets ‘on’ whenever the receiver receives a signal. It may be left unconnected.

You can also refer to this circuit diagram —

HT12D Decoder

The HT12D decoder is a CMOS LSI for remote control system applications. It will interface to RF receiver modules to create a secure single or multiple channel RF remote control receiver. The decoder receives serial addresses and data from a programmed encoder that are transmitted by a carrier using an RF or an IR transmission medium. The decoder compares the serial input data three times continuously with its local addresses. If no error or unmatched codes are found, the input data codes are decoded and then transferred to the output pins. The VT pin also goes high to indicate a valid transmission. The HT12D decoder is capable of decoding information that consist of N bits of address and 12-N bits of data. The HT12D is arranged to provide 8 address bits and 4 data bits.

Features:

• Operating voltage: 2.4V~12V
• Low power and high noise immunity CMOS technology
• Low standby current
• Capable of decoding 12 bits of information
• Binary address setting
• Received codes are checked 3 times
• Address/Data number combination: 8 address bits and 4 data bits
• Built-in oscillator needs only 5% resistor
• Valid transmission indicator
• Easy interface with an RF or an infrared transmission medium
• Minimal external components
• Secure and robust protocol
• Ideal for remote control and security applications
• Compatible with the HT12E encoder IC
• 18-pin DIP
• Applications
• Burglar alarm system
• Smoke and fire alarm system
• Garage door controllers
• Car door controllers
• Car alarm system
• Security system
• Cordless telephones

Pin Diagram and Description:

• VDD and VSS are  used to provide power to the IC, Positive and Negative of the power supply respectively. As I said earlier its operating voltage can be in the range 2.4V to 12V
• OSC1 and OSC2 are used to connect external resistor for internal oscillator of HT12D. OSC1 is the oscillator input pin and OSC2 is the oscillator output pin as shown in the figure below.

• A0 – A7 are the address input pins. Status of these pins should match with status of address pin in HT12E (used in transmitter) to receive the data. These pins can be connected to VSS or left open.
• DIN is the serial data input pin and can be connected to a RF receiver output.
• D8 – D11 are the data output pins. Status of these pins can be VSS or VDD depending upon the received serial data through pin DIN.
• VT stand for Valid Transmission. This output pin will be HIGH when valid data is available at D8 – D11 data output pins.

Working of HT12D:

HT12D decoder will be in standby mode initially ie, oscillator is disabled and a HIGH on DIN pin activates the oscillator. Thus the oscillator will be active when the decoder receives data transmitted by an encoder. The device starts decoding the input address and data. The decoder matches the received address three times continuously with the local address given to pin A0 – A7. If all matches, data bits are decoded and output pins D8 – D11 are activated. This valid data is indicated by making the pin VT (Valid Transmission) HIGH. This will continue till the address code becomes incorrect or no signal is received.

PRACTICAL CIRCUIT OF HT12D:

Download HT12D:Here

HT12E Encoder

       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. The chosen pair of encoder/decoder should have same number of addresses and data format.

       Simply put, HT12E converts the parallel inputs into serial output. 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. When a trigger signal is received on TE pin, the programmed addresses/data are transmitted together with the header bits via an RF or an infrared transmission medium. HT12E begins a 4-word transmission cycle upon receipt of a transmission enable. This cycle is repeated as long as TE is kept low. As soon as TE returns to high, the encoder output completes its final cycle and then stops.

Features:

• Operating voltage: 2.4V~12V
• Low power and high noise immunity CMOS technology
• Low standby current: 0.1uA (typ.) at VDD=5V
• Minimum transmission word: Four words
• Built-in oscillator, needs only 5% resistor
• Data code has positive polarity
• Minimal external components
• Secure and robust protocol
• Ideal for remote control and security applications
• Compatible with the HT12D decoder IC
• 18-pin DIP

Applications:

• Burglar alarm system
• Smoke and fire alarm system
• Garage door controllers
• Car door controllers
• Car alarm system
• Security system
• Cordless telephones

PIN DESCRIPTION OF IC HT12E: 

The pin Description of the IC HT12E was pretty simple to understand with total of 18 pins.

• VDD and VSS: Positive and negative power supply pins.
• OSC1 and OSC2: Input and output pins of the internal oscillator present inside the IC.
• TE: This pin is used for enabling the transmission, a low signal in this pin will enable the transission of data bits.
• A0 - A7: These are the input address pins used for secured transmission of this data. These pinns can be connected to VSS or left open.
• AD0 - AD3: This pins are feeding data into the the IC. These pins may be connected to VSS or may be left open for sending LOW or HIGH bits to the encoder.
• DOUT: The output of the encoder can be obtained through  this pin and can be connected to the RF transmitter.

WORKING OF IC HT12E: 

        HT12E starts working with a low signal on the TE pin. After receiving a low signal the HT12E starts the transmission of 4 data bits as shown in the timing diagram above. And the output cycle will repeats based on the status of the TE pin in the IC. If the TE pin retains the low signal the cycle repeats as long as the low signal in the TE pin exists. The encoder IC will be in standby mode if the TE pin is disabled and thus the status of this pin was necessary for encoding process. The address of these bits can be set through A0 - A7 and the same scheme should be used in decoders to  retrieve the signal bits.

PRACTICAL CIRCUIT OF HT12E:

         The above diagram shows the practical set up of the HT12E encoder IC for better understanding on the working.

        Share this IC working with others  through social sites if you like. Feel free to comment and post your queries regarding this post we are happy to assist you.

Download HT12E :Here