Voltmeters

A humidity sensor with temperature compensation built-in. Never apply a DC voltage to the sensor, even measuring the sensor with an ohmmeter will damage the device, always ensure that an AC voltage is applied. Avoid condensation, freezing, dust, mist, oil, alcohol, etc. To set up this circuit replace the H14DL with Min Res 22Kohm and Min Res 51Kohm as shown, Acjust RV1 until a voltmeter between output and ground reads 1.40V. The output will then be as shown in the table to an accuracy of about ~5%.

A Very Simple circuit and some Variations. Play with it. All parts are cheap and should be easily obtained. None are very critical.

Measures 10mV to 50Volt RMS in eight ranges. Simply connect to your Avo-meter set @ 50΅A range. Switching SW2 the four input ranges can be multiplied by 5.

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 kΩ to 1 MΩ.

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.

This is an easy to build, but nevertheless very accurate and useful digital voltmeter. It has been designed as a panel meter and can be used in DC power supplies or anywhere else it is necessary to have an accurate indication of the voltage present. The circuit employs the ADC (Analogue to Digital Converter) I.C. CL7107 made by INTERSIL. This IC incorporates in a 40 pin case all the circuitry necessary to convert an analogue signal to digital and can drive a series of four seven segment LED displays directly. The circuits built into the IC are an analogue to digital converter, a comparator, a clock, a decoder and a seven segment LED display driver. The circuit as it is described here can display any DC voltage in the range of 0-1999 Volts.

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 simple circuit makes it posible to monitor the charging process to a higher level. If you need more information then check out the LM3914 Datasheet. Final adjustsments are simple and the only thing needed is a digital voltmeter for the necessary accuracy.

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.

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.

The unit is quite inexpensive - two ICs and a couple of transistors. One of the ICs is an AT90S4433 AVR micro controller - also inexpensive, and quite powerful. A feature of this chip is that it has six 10-bit Analog to Digital conversion inputs, allowing measurements with a resolution of about 0.1% of full scale. The AT90S4433 processor used is now discontinued, but has been replaced with a cheaper, higher specified device which is largely code and pin compatable - the ATMEGA8.

The PIC16C71 is a member of the mid-range family of 8-bit, high-speed microcontrollers, namely the PIC16CXXX. The salient features of the PIC16C71 are: ? Improved and enhanced instruction set ? 14-bit instruction word ? Interrupt capability ? On-chip four channel, 8-bit A/D converter This application note demonstrates the capability of the PIC16C71. This application note has been broken down into four subsections: Multiplexing Four 7-Segment LED Displays Multiplexing Four 7-Segment LED Displays and Scanning a 4x4 Keypad Multiplexing Four 7-Segment LED Displays and the A/D Channel Multiplexing Four 7-Segment LED Displays with a 4x4 Keypad and 4 A/D Channels

This is an easy to build, but nevertheless very accurate and useful digital voltmeter. It has been designed as a panel meter and can be used in DC power supplies or anywhere else it is necessary to have an accurate indication of the voltage present. The circuit employs the ADC (Analogue to Digital Converter) I.C. CL7107 made by INTERSIL.

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.

This application note has been broken down into four subsections: Multiplexing Four 7-Segment LED Displays Multiplexing Four 7-Segment LED Displays and Scanning a 4x4 Keypad Multiplexing Four 7-Segment LED Displays and the A/D Channel Multiplexing Four 7-Segment LED Displays with a 4x4 Keypad and 4 A/D Channels

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.