single digit voltmeter by IC 4028, 4029 LM311
First bear it in mind that it is a single digit voltmeter which is 0-9 counts only on the positive side, that is it can measure +0 to +9V DC +/- 1V error. That may not be practical for the cost of the components above. It may be used as a toy logic probe. The reason for the circuit is not for usage, but to give design ideas. The methodology used is Gut Feel - Thumb Rule method. ……….
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Comparator Oscillator Circuit by LM311
LM311 Oscillator
The 4029 CMOS Counter IC
