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 —