Type of sensors used on our buggy

In the circuit we are going to use a Light Dependent Resistor. LDRs are usually used in light or dark sensor circuits. When the LDR is in the dark it can have a resistance of mega ohms, when the LDR is in light its resistance falls to just a few hundred ohms. It also works in the opposite way depending on how the circuit is wired up and where the LDR is placed in the circuit.

In our circuit we have decided to use 3 LEDs and 3LDRs. The LEDs were placed in front of the LDRs to get maximum feedback from the LDRs. As shown in one of the previous post the more LEDs and LDRs you have the better the line robot will perform in its task.

In the circuit design we were considering to use 3 white LEDs. You could use more LEDs but the 4.5 volts form the 3 AA batteries would not be enough to power the LEDs thus they would run out too quickly. If the battery was changes to a 9v battery we could have up to 5 strands of 2 white LEDs in parallel in a circuit but the battery would only last up to 5 hours.

Thus in the end we reverted back to our original idea and used 3 red LEDs and 3 LDRs. The robot was wired up such that as the robot passed along the black line the LEDs would be on (emitting light). The light from the LEDs would get reflected back towards the LDRs from the white background. Where the light was getting absorbed (along the black line) no light would be reflect to the LDR thus giving a pathway for the robot follow.

Pictured below is an example of how the LED will emit the light and how the LDR will receive it.