Voltmeters

Tests 1.5 to 15 Volt cells. This circuit runs a fast battery test without the need of power supply or expensive moving-coil voltmeters. It features two ranges: when SW1 is set as shown in the circuit diagram, the device can test 3V to 15V batteries. When SW1 is switched to the other position, only 1.5V cells can be tested. Two-LED display, no power supply required...

Measures 10mV to 50Volt RMS in eight ranges. Simply connect to your Avo-meter set to 50µA range. Connect J2 and J3 to an Avo-meter set to 50µA range. Switching SW2 the four input ranges will be multiplied by 5. Total fsd ranges are: 10mV, 50mV, 100mV, 500mV, 1V, 5V, 10V, 50V. Set R11 to read 1V in the 1V range, with a sine wave input of 1V @ 1KHz. Compare the reading with that of another known precision Millivoltmeter or with an oscilloscope...

This circuit is designed to provide an inexpensive way to to create a High Impedance Voltmeter while making use of an inexpensive analog or digital multimeter. When measuring voltages in high resistance circuits the resistance of the voltmeter itself has an effect on the circuit. For example if the voltage across a 1 megohm resistor is measured with a voltmeter that has an internal resistance of 1 megohm then the total resistance in that part of the circuit is effectively halved (two 1 M resistors in parallel = 500K ohms)...

The full-scale deflection of the universal high-input-resistance voltmeter circuit shown in the figure depends on the function switch position as follows: (a) 5V dc on position 1 (b) 5V ac rms in position 2 (c) 5V peak ac in position 3 (d) 5V ac peak-to-peak in position 4 The circuit is basically a voltage-to-current converter. The design procedure is as follows: Calculate RI according to the application from one of the following equations: (a) dc voltmeter: RIA = full-scale EDC/IFS (b) rms ac voltmeter (sine wave only): RIB = 0.9 full-scale ERMS/ IFS (c) Peak reading voltmeter (sine wave only): RIC = 0.636 full-scale EPK/IFS (d) Peak-to-peak ac voltmeter (sine wave only): RID = 0.318 full-scale EPK-TO-PK / IFS..

This digital voltmeter is ideal to use for measuring the output voltage of your DC power supply. It includes a 3.5-digit LED display with a negative voltage indicator. It measures DC voltages from 0 to 199.9V with a resolution of 0.1V. The voltmeter is based on single ICL7107 chip and may be fitted on a small 3cm x 7cm printed circuit board. The circuit should be supplied with a 5V voltage supply and consumes only around 25mA...

Have you ever wanted to find out how strong a magnet really was, or how the strength of the magnetic field varied as you changed the distance from the magnet or the temperature of the magnet, or how well a shield placed in front of the magnet worked? Voltmeters are fairly inexpensive and easy to find, but where do you purchase a Gaussmeter (also known as a magnetometer). I built a hand-held Gaussmeter for measuring the polarity and strength of a magnetic field. It uses a linear Hall effect device and some op-amps and resistors and things from Radio Shack...

Unlike carbon-zinc or alkaline cells, NiCd cells have a very flat discharge curve. This means that their output voltage remains relatively constant (ranging from about 1.28V down to 1.17V) until they are almost dead, and then drops off suddenly. Testing the voltage with an ordinary analog voltmeter is therefore nearly useless, because it will always read close to 1.2V no matter how much charge is left...

About a year ago, I bought a 5 Watt solar panel on sale at Harbor Freight. It`s an ICP Battery Saver Pro, and will supply about 15 Volts DC at 335 mA in full sunlight, which is about perfect for the 7 AH batteries I usually use for QRP portable. For a while, I just lashed-up some battery clips and wire, laid the solar panel on a lawn chair, and used a voltmeter to check the progress of the charging...

A simple circuit measures the open-circuit voltage, such as the expanded-scale voltmeter circuit in Figure 2, which follows the curve in Figure 1. Sealed lead-acid batteries are available in several sizes, from a single D size (2.5 Ahr) to multicell rectangular battery packs...

An AC millivoltmeter - calibrated in dB - with a range of 30V down to 3mV full scale (80dB range) would be extremely useful. Attach a microphone (electret mic capsules are quite good), and you have a relative sound level meter, even better if you have some way of calibration. The meter presented here has a very wide frequency range, and uses a switched attenuator for range adjustment. The attenuator uses the 30-10-3 sequence, which provides 10dB steps between ranges. The standard attenuator provides an input impedance of over 2M Ohms,..

This circuit was originally designed to measure the volume of fluid inside a medical syringe. As designed, it produces a zero to 5 volt output, corresponding to a capacitance change of about 10 picofarads. With a digital voltmeter, at its output, it can resolve a capacitance change of 0.002 picofarads or 2 femtofarads...

This Field Strength Meter is simple and also quite sensitive. It uses an ordinary digital voltmeter to measure RF signal strength up to a few hundred MHz. The multimeter should be set to the lowest dc volts range for maximum sensitivity. This is normally 200mV DC for most meters. The circuit works well at VHF (around 100MHz) and was quite pleased with the results. L1 was 7 turns on a quarter inch former with ferrite slug...

You need phase measurements to set up and verify electronic devices in amplifiers and in audio, control, ultrasound, and echo systems. Phase measurements can be problematic, because not many simple, inexpensive phase meters are available. Moreover, using an oscilloscope is time-consuming and imprecise. The phase meter described here uses a standard voltmeter as an output device. It measures the phase difference between two signals with better than 1% accuracy and it operates to 10 MHz...

From a high-volume-production point of view of the Design Idea `Test batteries without a voltmeter` (EDN, Nov 9, 2000, pg 167), it is a time-consuming and laborious task to tweak the large number of potentiometers on each of the comparator input references. An alternative to this onerous adjustment chore is to replace all potentiometers with 1%-tolerance fixed resistors (Figure 1). Before calculating each voltage-reference resistance value, you should use a reasonable selected total resistance value, RTOT, ranging from 100 k to 1 M...

Continuous monitoring of the mains voltage is required in many ap- plications such as manual voltage stabilisers and motor pumps. An analogue voltmeter, though cheap, has many disadvantages as it has moving parts and is sensitive to vibrations. The solidstate voltmeter circuit described here indicates the mains voltage with a resolution that is comparable to that of a general-purpose analogue voltmeter...