This learning board has the following features:
A 9V DC input socket with power on switch
Regulated +5V power supply using 7805 IC
3 output LEDs and 1 power on LED
2 input tact switches
2 potentiometers: one for analog input and the other for providing reference voltage for ADC
Transistor-based TTL-RS232 level converter for serial communication.
A DC motor with a transistor driver.
Most of these features on the board are accessible through female header pins. None of the 6-I/O pins of PIC12F683 are hardwired to anything and they are accessible through header pins too. The figures below show PIC12F683 pins, the type of female headers and jumpers used to make connection on the board, and the detail circuit diagram of the learning board. Only the ISCP pins are accessible through male header pins. The entire circuit is built on a 8 x 12 cm general prototyping board.
As you see the output LEDs have 470Ω current limiting resistors in series so that a PIC pin can be safely drive them. The piezo buzzer is also driven directly by a PIC pin through a series resistor. The DC motor, however, is connected as a load to the collector of S8050 transistor as the required current to drive the motor cannot be supplied by the PIC port. So, the PIC port can switch on the transistor by pulling its base HIGH and the collector current of the transistor provides the sufficient current to drive the motor.
The TTL to RS232 level converter and vice-versa is achieved with two transistors and few other components. The negative voltage required for RS232 level is stolen from the RS232 port of a PC itself. Note that there is no hardware UART inside PIC12F683, so the serial data transfer from the microcontroller to PC will be possible only through a software UART through any of GP0, GP1, GP2, GP4, and GP5 ports (GP3 is input only). The transmitter and receiver port on microcontroller side are denoted by uTx and uRx, whereas on the PC side are denoted by Tx and Rx, respectively.
The circuit diagram shows that the two input tact switches with the two potentiometer outputs and all the eight PIC12F683 pins are accessible through female headers. The tact switches are active low, i.e., under normal condition, a tact switch output is HIGH and when it is pressed, the output is LOW. There are couple of extra headers for Vcc and Gnd terminals which may be required while doing experiments.
The power supply circuit is the standard circuit of 7805 regulator IC. A power-on LED is connected across Vcc and Gnd with a 470Ω series resistor.
The in-circuit serial programming (ICSP) of PIC12F683 can be done with two pins: ICSPDAT (pin 7), and ICSPCLK (pin 6). The programming voltage, Vpp, should be provided to pin 4 of PIC12F683 while programming. All the required ISCP pins are available through a male header, so the PIC can be programmed through any ICSP PIC programmer. Make sure that the sequence of ISCP pins on the programmer side and our learning board match.
Important: During ICSP, pins 4, 6, and 7 of PIC12F683 should not be connected to anything; leave them open so that there won’t be any voltage conflict between the programmer and the external circuit.