This circuit is used to measure the voltage on a 12V (nominal) lead acid rechargeable battery system. It was specifically designed for use in solar powered systems, but is general enough that it can be used for automotive or other 12V systems. Lead acid batteries normally spend their working lifetime in the voltage range of 11-15 Volts. This meter circuit was designed to show the voltage range of 10-15V on an analog meter movement, it can be used to show the battery charge state from empty to full. source

This is a low power voltmeter circuit that can be used with alternative energy systems that run on 12 and 24 volt batteries. The voltmeter is an expanded scale type that indicates small voltage steps over the 10 to 16 volt range for 12 volt batteries and over the 22 to 32 volt range for 24 volt batteries. Power consumption can be as low as 14mw when operated from 12V and 160mw when operated from 24V.It is possible to set the meter to read equal steps across a variety of upper and lower voltages.source

The circuit acts like a magnifying glass on part of the scale of an ordinary meter, namely the part of the scale we are interested in. For example, an ESV for testing a single NiCd cell would range from 1.17V at one end of the scale to 1.28V at the other end of the scale. With the full scale covering this narrow range, it’s easy to see voltage changes within the range.The circuit described here uses a bar graph display consisting of eight LEDs.source

Many applications call for measuring ac lines or high dc voltages. One common technique uses a large voltage divider followed by a buffer.A third solution yields high-accuracy, high-voltage measurements (Fig. 1). The integrator (OP177) supplies negative feedback around the difference amplifier (AD629), forcing its output to stay at 0 V. source

This is a simple serial volt meter circuit.It can measure from 0 to 5 volts DC.The software for the serial voltmeter monitors the serial port for incoming information sent by the PIC micro. Once received, the displayed result is calculated by taking the value received and multiplying it by 0.02. The PIC16C71 A/D converter is the successive approximation type and provides an 8-Bit result. With only an 8-Bit result our range is limited from 0 to 255 that represents from 0 to 5 volts respectively. source