This unit delivers 0 to 20 volts at up to 4 amps in 0.1 volt increments. The entire device runs on a PIC16F870 (about $3 in small quantities). This is basically a switching power supply with the voltage regulation done in software. The PIC used here has analog inputs (used to measure voltage and current) and hardware PWM (pulse width modulation) output used to control the power.
Only two controls are used on the front panel - an ‘on/off” push button and a rotary encoder. The on/off button is a ’soft’ control; the unit actually stays powered up all of the time. In the ‘off” mode, the display is blanked except for the far right decimal which acts as a standby indicator, and the voltage output is set to zero. Also, while in this mode, the rotary encoder is not active so that the previously selected voltage will be maintained when the unit is powered back on.
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