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  • Light Seeking Robot

  • Created: May 23, 2016

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This reference design features a circuit for a robot that moves according to the light it detects. In electronics, there are many ways to control a robot. Majority of them uses a microcontroller to control the motor driver that is controlling the wheels of the robot. In this design, two operational amplifiers inside the MCP6002T-I/SN device direct the motor driver. The control of these two operational amplifiers over the motor driver depends on the photodiodes used in the circuit.

The circuit in this design is just a basic application of an op amp as a comparator. The whole circuit is composed of photodiodes, MCP6002T-I/SN, L293DNE DC motor driver, indicators, 6P screw terminal block, and power supply protection/filter. The photodiodes are used in the circuit as light sensors. The MCP6002T-I/SN has two internal op amps that are configured as comparators. It compares the two voltages across the non-inverting and inverting terminal inputs, and outputs a signal if ever the voltage across the non-inverting terminal is greater than the inverting terminal. Initially, when there is still no light, the voltages across the inverting terminal inputs of MCP6002T-I/SN must be calibrated through P1 and P2 potentiometers. The voltages across the inverting terminal inputs must be greater than the non-inverting terminal but not too much so that when the photodiodes detect a light, the voltages across the non-inverting terminal inputs will exceed the voltages across the inverting terminal inputs. The outputs of the MCP6002T-I/SN op amps are connected to the L293DNE motor driver inputs and serve as controls for the direction of the robot wheels.

The movement of the robot depends on the photodiodes. Assuming that DC motor M1 is assigned for the left wheel and DC motor M2 is assigned for the right wheel, the photodiode D1 is assigned for M1 or turning right movement and D2 is responsible for M2 or turning left movement. If there is no light detected by D1 and D2, the robot will just standby or does nothing. If only D1 detects light, the robot will turn right since only M1 will rotate and if only D2 detects light, the robot will turn left since only M2 rotates. If both of the photodiodes D1 and D2 detect light, the robot will move forward because both of the DC motors M1 and M2 rotate. The whole circuit must be powered by a 6V battery or four double A batteries connected in series to ensure that the supply for the op amp doesn’t exceed to its absolute maximum rating. The voltage drop across diode D3 also helps in avoiding the power supply limit of the op amp and protects the whole circuit from reverse polarity.