Since it took a while to get the compilation to run through, I want to document the the process.
Continue reading]]>But they most of them share a problem: their probing voltage is too high. They are designed to even turn on a LED, so most meter use a probing voltage of 2 volts, and may go up to 3 V. In my collection only my old and cheap DT-4000ZC uses a probing voltage of 0.44V, all the others are around 2.9V. Why is that a problem, and what can we do about it?
Continue reading]]>But then my mind wandered and I realized that the two oscillators were actually PWM generators. And then I it was only a small step to “this can be implemented in a PSoC much better”. So I went ahead and tried it.
Continue reading]]>But they all rely on manual frequency setting, and their accuracy is in the single digit percent range (maybe as good as 0.1%). If you want to have a stable frequency source, you need a crystal based oscillator - and that typically means using a DDS chip.
When I needed a small frequency generator for a project several years ago, I did neither had the time nor the skills to build something like that. But I had in my parts box a nice chip that seemed perfect for a small tool - the SPG8640BN.
Continue reading]]>But I got new transmitter coils from Würth in the mean time, and did some experiments with them (which need a write-up).
Apart from that I have finalized my schematic, and added all the missing details I already explained the most important parts of it, but there are still some minor tweaks here and there. So there will be a separate post about it.
Continue reading]]>Seeing this I did something similar - but I used a REF5020 from TI instead:
but it was not as accurate as I would have liked (the initial accuracy is 0.1%), and the 2.048 Vv output voltage meant that its just over the range for a 2000 counts multimeter (so it read 2.05).
So when I bought a new multimeter last fall (two UT61E actually), I looked into building a new, more accurate reference, with a wider range of voltages.
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