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A milli Amp analog meter often used along with audio system can be easily converted into a decent volt meter, all that is needed is an understanding of the requirement and the meter. In case a 10V full scale meter is to be designed, then a 10K resistance is to be put in series with the meter coil so that for an applied voltage of 10V a meter can receive 1milliAmp only. The meter itself has an internal resistance and if that is measured properly then in actual practice the resistor to be connected in series shall be having a value of 1000 ohms – IR (internal resistance of the meter). When we measure smaller voltage then this internal resistance of the meter plays a significant role, say for this particular case the internal resistance is 86 ohms, hence, for a I.V. full scale meter the value of the external resistance would be (1000-86) 914 ohms. The milli amp meter can also be used as an Amp meter of higher currents by adding shunt resistances. This is being achieved by simple net...

This is a simple LED Voltmeter Circuit Diagram. Four µ741 op-amps are used here to measure the voltage ranging from 3V to 12V DC. The voltage measured is displayed on eight LEDs. The inverting inputs (pin 2) of IC1 through IC4 are supplied with regulated 12V DC through voltage dividers R1 through R4. So the inverting input of each op-amp forms the reference voltage. The non-inverting inputs (pin 3) of the op-amps are tied together and connected to the input terminals. The voltage to be meaured is fed to these input terminals. When the input voltage exceeds the reference voltage of any of the op-amps, its output goes high, making the corresponding LED s to glow. This circuit is designed to measure 3V, 6V, 9V and 12V DC. For instance, when the input voltage is 3V, LED 7 and LED8 glow. When the input voltage is 12V, all the LED s glow. Note. You can use a quad device such as LM324 instead of µ741 IC s.  LED Voltmeter Circuit Diagram

A  voltmeter  is an instrument used for measuring the electrical potential difference between two points in an electric circuit. Analog voltmeters move a pointer across a scale in proportion to the voltage of the circuit; digital voltmeters give a numerical display of voltage by use of an analog to digital converter. Voltmeters are made in a wide range of styles. Instruments permanently mounted in a panel are used to monitor generators or other fixed apparatus. Portable instruments, usually equipped to also measure current and resistance in the form of a multimeter, are standard test instruments used in electrical and electronics work. Any measurement that can be converted to a voltage can be displayed on a meter that is suitably calibrated; for example, pressure, temperature, flow or level in a chemical process plant. General purpose analog voltmeters may have an accuracy of a few per cent of full scale, and are used with voltages from a fraction of a volt...