This is a simple use of internal ADC of AVR atmega8. Voltage is measured directly with help of resistor divider and amperes is calculated based on the voltage drop in a low resistance power resistor.
Atmega8 based Volt – Ampere meter - [Link]
PIC Voltmeter Amperemeter can measure voltage 0-70V or 0-500V with 100mV resolution and current consumption 0-10A or more with 10mA resolution. The meter is a perfect addition to any power supply, battery chargers and other electronic projects where voltage and current must be monitored. The meter uses PIC16F876A microcontroller with built-in ADC (Analog to Digital Converter) and 16×2 green backlighted LCD display. With slight modification it is possible to measure higher voltage and current.
PIC Volt Ampere Meter – [Link]