Electrical System
Our electrical circuit was based off of previous circuits used in previous labs centered around a PIC18F2455 microcontroller. The final goal of the project was to place the completed circuit on a protoboard which would fit inside the completed project box, and power it using standard batteries for better usage away from power supplies, and greater portability.
To power the circuit with batteries, a voltage regulator was needed. Since the PIC and servos run off of 5 volts, the 7805A was chosen after consultation with Professor Brad Minch and powered with 6 AA batteries. It was connected to the circuit as directed in the data sheet by the fixed output regulator circuit, and is shown below. (Data Sheet and Diagram) On the input side battery voltage was applied which output approximately 5 Volts. The 7805A requires an input of at least 7 V to output the correct voltage with a maximum of 35 V.
Figure 1: 7805A Voltage Regulation Circuit
The control circuit centered around the PIC powered using the 7805A's output voltage as a voltage source. The user interface used 5 switches to control the servo motors, all of which were hooked up to pins 3-7 and grounded through a resistor. Two digital output pins were used to communicate with the servos, while the serial LCD module used the hardware serial module. Both the servos and the LCD used the 7805's regulated voltage for power.
Figure 2: Constructed Project Box Lid
The only complications faced with circuitry were when recreating the circuit on a board to fit into the project box. The circuit was cleanly installed and prepared to work except for pins 19 and 20 on the PIC were not connected to ground and +5 Volts respectively. This fact caused the PIC to not work while on the proto board, while it still continued to work on the solderless bread board. It appeared to be a clock problem, with the PIC not keeping the correct time. The installation of a new crystal oscillator proved futile. Upon careful inspection of the circuit, it was discovered that the pins were not connected as they should have been. During the transitions back and forth between boards to diagnose the problem, the serial LCD was damaged causing the only method of input for the final product to be useless. A new serial LCD has been swapped in, but the crystal oscillator remains broken, stranding our project on a breadboard.