This Project is built around the PIC Microcontroller 16F877 and uses different settings of the PWM output to derive a programmable power supply. There are two modes of operation, the first is based on setting the PWM value using three BCD Thumb Wheel switches and the Second sets the PWM based on a serial command using RS232.
In operation the PWM output is averaged using an RC filter and fed to an noninverting Op Amp stage with gain set such that at a power supply voltage of 5V and a PWM value of 999 the Op Amp output is 9.99V. This output is fed to an inverting stage to derive -ive 9.99V.
Thus variation of the PWM value from 0 to 999 provides simultaneous +ive and -ive outputs from 0 to 9.99V with a10 Bit resolution corresponding to 10mV/ Bit.
The PIC on initial switch ON checks for the BCD switch value, if it reads 000 then it goes into the RS232 control mode, or else it goes into the BCD switch control mode.