Voltmeters

This simple circuit makes it posible to monitor the charging process to a higher level. Final adjustsments are simple and the only thing needed is a digital voltmeter for the necessary accuracy. Connect an input voltage of 12.65 volt between the positive and negative poles and adjust the 10K trimmer potentiometer until Led 10 lights up. Lower the voltage and in sequence all other Led's will light up. Check that Led 1 lights up at approximately 11.89 volts.

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 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

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.

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,

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.

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.

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.

The circuit shown on this page is a reasonably Low Cost and moderately Hi-Tech ammeter for use with DCC systems. The circuit's meter output is always has the same polarity regardless of the input polarity. This allows a low cost DC voltmeter to be used to monitor a DCC current. The circuit uses ZETEX - ZXCT1009 - three terminal current monitor integrated circuits and can be operated in circuits of 7 to 20 volts.

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.