4 Wireless Keypad Control

4 Wireless Keypad Control


As the name indicates, SLIM-BOT, is a small, simple, compact robot, which may be moved or controlled using various inputs, without using any micro-controller. There is no need of programming language or coding to make and control the Slim-Bot. This is the basic project for those, who don’t have any knowledge in micro-controllers and programming. The various controls for the Slim-Bot is completely based on the electronic circuits only.

A robot may be controlled wirelessly in many ways. Here, the Slim-Bot is wirelessly controlled using a 4 button keypad. Four buttons are used as input system to control the movement of the Slim-Bot, which generates 4 bit code. Then the code is encoded using an Encoder IC (HT12E) and outputs the code in serial format. Then the serial output of the encoder is transmitted by an RF transmitter.

The serial data is received by the RF receiver and send the data to Decoder IC (HT12D). The Decoder IC, decodes the received serial data, back in to 4 bit data. The 4 bit data is used to control the movement of the Slim-Bot.


About Keypad Transmitter:

For simplicity and easy understanding of working of a keypad, a simple four direction keypad is made here. Four numbers of two pin tactile button switches are arranged in North-South-East-West (for Forward-Backward-Right Turn-Left Turn movements respectively) format and the connected as shown below.

The Backward, Right turn and Left Turn button press signals are directly fed to the Encoder IC (HT12E). Whereas for Forward movement, two diodes are connected from North button, to right and left buttons, to have movement of both right and left motors forward, thus the Slim-Bot moves forward.

The Encoder IC, HT12E, has 12 inputs, i.e., 8 address pins A0 to A7 and 4 data pins AD8 to AD11. All the 8 address pins are internally connected to logic high. To make a specific 8 bit address (or code to select matching Decoder IC, HT12D), required pins may be connected to ground. Here, all the pins are left open to get address as 11111111 binary code (= FF hexadecimal). The TE pin (pin 14), Transmit Enable, is connected to ground for continuous transmission of the button code.

The 4 bit button press code is fed to AD8 to AD11 pins of Encoder IC, HT12E, and the encoder generates, a serial data at Dout pin (pin 17), which contains the 8 bit address code and 4 bit data code sequentially.

The serial data is then sent to an RF (Radio Frequency) module. You may use either 433MHz or 315MHz RF module for the purpose. A good antenna increases transmission range of radio frequency.


About Receiver Board:

The radio frequency is received by an RF receiver module (should match the RF transmitter frequency 433MHz or 315MHz), and the 12 bit serial code is sent to Din pin of Decoder IC, HT12D.

Similar to the Encoder IC, the Decoder IC (HT12D) also has 8 bit address pins (A0 to A7) and 4 bit data pins (AD8 to AD11). The 8 bit address pins of decoder IC, shall match the address code pattern of the encoder IC, i.e., the same pins of decoder IC should be connected to ground, matching to encoder IC. Then, the 4 bit data is available at AD8 to AD11 pins of Decoder IC. The VT pin (Valid Transmission) goes high, whenever the received data is matching to the set address pattern at A0 to A7 pins. As the 8 address pins of Encoder IC are left open (not connected to ground) for the transmitter, here also the 8 address pins of Decoder IC are left open, to match the address, i.e., binary code = 11111111 (= FF hexadecimal).

So, the 4 bit signal data available at AD8 to AD11 pins are connected to the D0 to D3 pins of base board on Slim-Bot as shown below, to control the movement of the Slim-Bot. Here, the Decoder IC and RF receiver module may be directly soldered on the Base Board (PCB) of the Slim-Bot, or soldered on a separate board, then insert in to the 8 pin berg-strip available on the Base Board. 

A separate 3.7V Li-Ion battery may be used for the power supply of Decoder IC and RF module, to reduce interference to RF signals and isolate from the motors power supply.  Additional battery is connected between the Vcc and ground, through a switch in series as shown in the circuit and the shorting jumper shall be disconnected on the base board.

CLICK HERE to know, how to make BASE for SLIM-BOT.