Using timer of single microcontroller to design PWM to realize cheap and high resolution D/A converter

A sort of software design method that uses the internal timer/counter of 8051 series single chip microprocessor to make high resolution is introduced.The hardware circuit that can convert PWM signal to DC signal is designed.Using 12 bits D/A converter as design aim,all of the software and hardware as well as the datum of experimental results are listed.The accuracy reaches to 0.03%,and the cost is extremely low.