I was thinking the other day that if you got a precision voltage to current converter like the AD650;
https://www.analog.com/en/products/...rs/voltage-to-frequency-converters/ad650.html
It would be quite easy to make a high resolution digital voltmeter by feeding the output of the VFC into a frequency counter. For example with the AD650 with linearity of 0.002% up to 10Khz, equivalent to the resolution a 50 000 count voltmeter. It would require precision input switching, etc. But still a whole lot cheaper than buying a meter with this resolution. Obviously you need to have via frequency counter with at least 5 digits resolution.
Any thoughts???
Hi,
Back in the 1980's that's exactly what i set out to do, only using the 9400 frequency to voltage chip which had made use of the typical charge pump method. It was a pretty good chip, not sure if it is around anymore or not. I even built a home made discrete TTL based 8 digit LED frequency counter to use for measuring the output frequency and thus the voltage, i still have it today.
But that was in the *1980's*. Today we have 16 bit SD ADC converters that dont cost much, and i think they now go up to 32 bits. So technology improved in some areas that makes it more feasible to go with a more direct approach like an ADC (analog to digital converter).
You still need a display, like the 1602 LCD for example, unless you want to interface to the PC computer or Tablet and use that as your display and analysis bed.
Also, the FTV converters are not as stable as we would like to see for use as say a voltmeter because the frequency varies even when the input voltage does not vary because the conversion is not 100 percent repeatable. Thus to get a stable reading you'd have to average over several output samples with say a microcontroller chip.
I am currently working on and off on a project to create a voltmeter that interfaces with the Tablet computer. I have the interface working now but still need to do more work on the tablet graphics. The nice thing about doing it this way too is you can create four input channels which means you can monitor four voltages at the same time rather than just one. I need this functionality sometimes and built it into a PC interface unit i've had for years now (using a PIC chip however). On the Tablet it will be more portable as the whole thing can run on batteries.
So check out some modern ADC chips and see what you think. The variety is almost overwhelming these days. You can get up to 24 bits pretty cheap for use when making DC measurements, and for a scope type application you can get 1GSPS units (one gigasamples per second) although the cost is much higher. The scope i was building some 20 years ago was going to have a 100MSPS ADC at the heart, but technology improved the speed grade too a lot. That would be considered slow today.
One more small point...
With today's micro controllers you can build a voltmeter just using the chip alone because it's got an ADC built in, and send the readings over RS232 to the PC computer so you dont even need a display. The PIC chips have 10 bit ADC's built in, and the ARM chip has a 12 bit ADC built in. You might also get a DAC to create test signals of various waveshapes as part of the volt meter.
Let us know what you end up doing, should be interesting.