31/2-Digit Smd Voltmeter

31/2-DIGIT SMD VOLTMETER T. Wigmore This little circuit is simple to build, offers good accuracy and can be used in all applications requiring a small voltmeter with a clear LED read-out. Much of today"s electronic equipment re- quires a digital read-out to show system status or process variables. Such read- outs are usually compact voltmeter mo- dules with an LC (liquid crystal) display. The present read-out is also a voltmeter, but uses displays with light- emitting diode (LED) segments. A LED indication was chosen for this application because it remains visible in the dark (this require- ment would also have been met by an LCD with back-lighting). Also, the use of 7-segment LED displays in combination with a drive circuit built with SMA (sur- face-mount assembly) components allows a really compact voltmeter to be realized - see Fig. 1. This is particularly import- ant if the meter is to be built into existing equipment. One integrated circuit The circuit (Fig. 2) is formed by...