Microcontroller, JFET form low-cost, two-digit millivoltmeter

Benabadji, Noureddine
June 2006
EDN;6/22/2006, Vol. 51 Issue 13, p71
Trade Publication
The article discusses how to build a low-cost, two-digit direct current millivoltmeter from microcontroller and junction field effect transistor. Two-digit millivoltmeter provides flexibility and lends its to customization. An internal analog-to-digital converter can be incorporated into Microchip's PIC16F84A by connecting capacitor C3 between lines RB7 (output) and RA4 (input) and in series with an equivalent resistor. Some devices in the BF245 family have a less pronounced change of resistance versus gate-to-source voltage. To correct the measurement inherent in gate-to-source voltage versus drain-to-source on resistance transfer, the microprocessor's software feature a 100-point table that contain correction for two-digit display.


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