This was designed, keeping in mind, that sometimes we have few components available and you could not carry your DMM somewhere, but you have to make some instrument for a quick need with what is available.
Analog Dial AVO Amps-Volts-Ohms meter
IC3 LM555 is to generate -5V from 9V. That reminds me of a story, I came across a Book called CMOS Hot Ideas of Intersil. I had a chance to observe, build and learn some things here. The ICL7107 circuit was the most fascinating, I also read the books of National Semiconductor at that time.
In those days small firms used to make DPM's digital panel meters with 7107. In 1987 when i got a oppurtunity to design a DPM for a firm, I put the 555 clock in place CD4009 clock shown in intersil, to derive the -5.
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