Introduction: Simple Light Seeking Robot

Building the robot

This robot was designed as a project for secondary school pupils to build on an activity day.  The chassis was provided to the pupils pre cut.  The entire cost of the components per robot was just under GBP5 including the batteries.

The robot shown in the picture is the prototype shown with different LDRs and the batteries not in a holder.

The robot you are going to build is a simple light seeking robot that will run towards a light source or can be made follow a moving light source.

The robot is built on a small aluminium chassis and has two motors to move the robot left or right and two light dependent resistors used as light sensors. If the robot senses light with the left sensor it will drive the right motor to turn the robot left and visa versa. If both light sensors receive equal amounts of light both motors will be driven to move the robot forward. The two variable resistors are used to adjust the sensitivity of each channel. The transistors are used to amplify the small current flowing through the light dependent resistor to enable the current to drive the motor

Step 1: Building the Circuit

The main circuitry for the robot will be on stripboard. Stripboard consists of an insulating board with a square grid of holes drilled in it. Strips of copper link each row of holes, components such as resistors and transistors can be mounted on the plain side of the board with connecting wires passing through the holes. These wires are then soldered to the copper strip.

To solder onto the stripboard pass the wire ends of the components or connecting wire through the correct hole, you can bend the ends of the lead over slightly so that component does not fall out when you turn the board over. Hold the soldering iron so that the bit is against the copper strip of the stripboard and the wire of the component. Touch both with the resin cored solder just long enough for the solder to flow freely. Be careful not to over heat the components or board, then remove the soldering iron and wait for the joint to cool. Now cut off the surplus wire as close to the board as possible. Be careful to hold the end of wire to stop it flying into the air.

The robot is built on a small piece of 0.1 in matrix stripboard 13 strips by 17 holes. Some of the strips need to have breaks in them as shown in diagram. These breaks are made using a twist drill, these breaks are already made for you, the switch is also soldered onto the board.

The components can now be soldered to the circuit board, the position of the components is shown in the diagram.

Once the circuit is complete you will need to solder connecting wires to it, the position for these wires is shown in the diagram.

Step 2: Assembly

The circuit board can now be mounted on the chassis using the supplied nuts and bolts as shown in the diagram.

The battery holder can now be bolted to the chassis, a short length of stiff wire is trapped under the front of the battery box to support the light dependent resistors. The motors can the be fixed to chassis with tie wraps and all the interconnecting wires can be soldered to the relevant locations.

The general layout and motor and battery wiring are shown in the diagram. Pay special attention to the polarity of the motors, if they are connected incorrectly the robot will go round in circle or may even go backwards.

To increase the traction of the robot, tyres need to be fitted these consist of piece of PVC sleeving over the motor shaft followed by a piece of rubber tubing as shown in cross section in the diagram.

Step 3: Bill of Materials


R1 100

R2 100

R3 100

R4 100

VR1 2.5k

VR2 2.5k


TR1 BC178

TR2 BC178



LDR1 NSL-19M51

LDR2 NSL-19M51


Battery Holder

Batteries AA Qty2

Motors 3volt Qty2


Veroboard 17 holes by 13 strips

Tiewraps for holding motor Qty2

Small tiewraps for holding LDR Qty2

Nuts and bolts

Aluminium chassis

Connecting wire

Sleeving and rubber tube for wheels

Short piece of stiff wire for holding LDR