Today I want to explain my last DIY project. I found myself in the situation of needing many voltmeters, but i have at home only one multimeter. So i said "why i don't make myself a multiple voltmeter for this type of jobs?!".
It's a simple voltmeter using ATMega328p microcontroller and four circuits with voltage dividers and Zener diode. The output signal of this circuit, will be a voltage in range of 0 to 5VDC, perfet for the analog inputs of my ATMega328p. It can read DC current in range of 0-50VDC.
To make it portable, i put the project in a box with 4 inputs and one display 16x2 LCD, all supplied by a 9V battery. In this way, I can put it in my bag of tools!
I haven't and Arduino, but i programming the atmel's microcontroller with Raspberry B+ and the SPI comunication system. For this reason, in the schematic you can find four additional pins connected to reset, MISO, MOSI and SCL of the ATMega328p.
The code is included in the attachments, in .ino file (for Arduino), but you can find .hex file in temporary files directory in windows os systems after compiling by Arduino editor. The code requires an improvement in the accuracy of reading. Also there is the schematics for Eagle.