Autoranging Digital Multimeter

Digital multimeters are now- adays offered in many different styles and at very competitive prices. In spite of this, many enthusiasts remain convinced that building good quality test equipment for use in their workshop is a very rewarding pastime. The digital multimeter pro- posed in this article is a ver- satile and remarkably user- friendly test instrument that has some features not commonly found in its price bracket. Circuit description The Type ICL7139 from GE- Intersil is a recently introduced, high performance, low power, autoranging digital multimeter IC, whose main technical data are summarized in Table 1. When used as a DC voltmeter, the ICL7139 always displays the result of a conversion on the correct range. As can be seen from the front panel for the multimeter, shown in Fig. 3, the mode selector has but a single position for DC and AC voltage measurements. When set to DC voltage, the ICL7139 automati- cally selects one of four ranges to ensure optimum accuracy of the...