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.
To make Slim-Bot, smaller and compact, two numbers of servo motors are modified to make continuous rotation. You may use SG90 or MG90 servo motors for the purpose. Two small wheels are used as drive wheels, connected on either side (at rear), to the modified servo motors, and a small castor wheel is used at the front for the Slim-Bot.
To make the Robot compact, a 3.7V flat Li-Ion cell, (normally available in old cell phones), is used and positioned below the main PCB. The size of the main PCB is also made small, which will accommodate mainly, motor controller IC (L293D), power switch, an 8 pin connector for data and power supply, an indicator LED etc. The pinouts of 8 pin female connector is shown below. A shorting jumper is used to connect the DC power supply to both the motors (through L293D) at Vmot to Vcc pin. But, a separate power supply may be used for Vcc pin, if required, in future control systems.
About Base Board :
The base board is a small PCB, which holds the basic required electronic components and connections. The main component on the base board is, motor driver IC, L293D. similarly, the main connection is a 8 pin female berg strip. Out of 8 pins, 4 pins are data input pins for motor control and DC power supply pins on one side and motor power supply side on other side. The shorting jumper J1 is connected to get the power supply at Vcc pin (power supply to external PCB, if any) also, along with Vmot pin (for motor power supply) and Logic power supply (VccL) of motor driver IC.
The logical data inputs, D0, D1, D2 and D3, are connected to 4 inputs, ip1, ip2, ip3 and ip4 pins of motor driver IC. Whereas, the output pins, op1, op2, op3 and op4 are connected to two modified servo (DC) motors, for movement control of the Slim-Bot. So, for movement control of the Slim-Bot, four bit signal(s) are used at D0 to D3 pins on the 8 pin berg strip.
The Slim-Bot uses three wheels, out of which two small wheels are directly mounted on the modified servo motor shaft, and the third one is a small castor wheel, which is fixed at the front side of the Slim-Bot.
For quick testing of motor movement, the D0 to D3 pins may be connected sequentially to Vcc pin, through a series resistor (about 1K). For each pin connection of D0 to D3, one out of the two motors, rotates either Clockwise or Anti-clockwise.
About IR follower :
IR or Infra-Red sensor LED is sensitive to the IR light falling on its surface. The resistance between the Anode and Cathode pins varies due to intensity of IR light falling on it. The resistance decreases, as the IR light falling on it is high and vice-versa. The IR sensor LED should be connected in reverse polarity (i.e., cathode towards positive power supply and anode towards ground or negative power supply), for its proper functioning.
Two 5mm size, IR LEDs are used here, to control the Slim-Bot using IR light. Both the IR LEDs are connected in reverse polarity as shown in the circuit diagram below. The Cathode (C) pins are connected to Vcc and Vmot, and Anode (A) pins are connected to D0 and D3 in crossed manner. Note that, the Anode pins of both the IR LEDs should not touch each other. A small opaque medium (block or barrier) is introduced between the two IR LEDs, to reduce the IR light interference on each other.
Now, when, an IR light is falling on the left side IR sensor LED, the signal goes to right side data pin (D3) and right side motor rotates accordingly. This makes Slim-Bot to have left side turn, towards the IR light. Similarly, the right side IR light makes, the Slim-Bot to take right turn. When the IR light falls on both the IR sensor LEDs (if the IR light source is in front of Slim-Bot), then both the motors rotates and the Slim-Bot moves forward.