This is an upgrade to recently published Simple Digital Voltmeter.Few improvements were done to hardware and software.DVM operating range was slightly increased up to 24 V Max, however the most significant change is that the code now uses full 10 bit of ADC resolution to calculate the voltage being measured allowing 3 Digit result for 0-9.99 range and 4 digits for 10.00-24.00 range. Also generic Common Cathode 7-Segments were used as they are widely available and can be purchased on Ebay for example. Operational amplifier LM358 and simple RC low pass filter were added to PIC analog input AN1 (Channel 1) to improve circuit stability. Only a simple calibration is needed. Connect 5V to the input, calibrate R1 to display 5.00 V. See attached picture comparing measurement to Fluke 87 V. Prototype has good accuracy if calibrated correctly.
PIC16F877A was used again for this design as other PIC models were not available during development stage. If this project will generate enough interest I’ll modify the schematic/code to work with other microcontrollers. Any PIC with 10 bit ADC and 11 available I/O pins can be configured as DVM.