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Recent content by sn00p

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    Measuring small resistances.

    Love this, honestly it's a really great hobby because with a few components you can make things that do things and you have something tangible. Seems @Touring_Rob got you on the right path! I know that it's hard to get over the "Chinese made crap" thing, but they really do crank out decent...
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    Measuring small resistances.

    Off topic…but it’s my thread…:) Saturday I built up the LTZ1000A reference, there was a definite squeaky bum time when it came to soldering the reference. Currently it’s hanging off the front of my top 34401a and also fed into the second one, horrible cabling and no shielding although I did...
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    Measuring small resistances.

    Yeah, I’ll patch in a 20-bit one, it needs MOSI (to do anything other than just return conversions) but all the digital signals to the analog board have bidirectional level translators it’s easy to patch that onto the ADC and I can try both feeding in the raw + amplified signal.
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    Measuring small resistances.

    I will also do some tests with the LTC2480 as the main ADC since it has a programmable gain amplifier built in, although it’s only 20-bit, I can stretch those bits further than I can on the 24-bit, it may be a better solution. It’s also cheaper and availability isn’t an issue. The analog board...
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    Measuring small resistances.

    this project has been a real godsend in keeping my mind occupied over the past month, I have made a couple more changes, so one of the sense resistors is lifted and there’s an additional 100 ohm resistor (well, it’s 2 50ohm in series) on the rear and a trim pot. I broke out the measurement...
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    Measuring small resistances.

    Got some DPDT relays coming over the next couple of days, I don’t have stripboard or JST XH connectors here, left them all at home…..so had to buy another set of them, and another strip board cutter, and stripboatd, and 2.54mm single in-line connectors and….you get the picture, all stuff I have...
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    Measuring small resistances.

    sometimes you can’t beat pencil and paper, or in this case, ipad and Apple Pencil, it’s way easier to noodle parts or ideas on the iPad than it is sitting in KiCad trying to find parts, put wires and so on. since deciding not to move all the calibration stuff to the analog board, I grabbed a...
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    Measuring small resistances.

    f**king KiCad strikes again, I’ve seen this before, a net that for whatever reason it decides to not connect between sheets, it’s done it before to me and it did it again on this. The 5V ref on this is powered directly by VIN, it decided that VIN on two different sheets were not connected, and...
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    Measuring small resistances.

    I'm a f**king idiot. I reposted the same link. This I what I meant to post. https://www.edn.com/dc-accurate-32-bit-dac-achieves-32-bit-resolution/ It uses the sum of two PWM signals to produce a "32-bit" DAC, one is a coarse PWM and the other is a fine PWM and I've seen this article cited in...
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    Measuring small resistances.

    Yeah…my brain is all over the place. https://xdevs.com/article/kx-ref/ The stability is the big thing here as you know, especially where the TC is concerned, this design is apparently very good, the LTZ1000ACH is used in the 8.5 digit meter HP/Agilent/Keysight have sold that I’ve forgotten the...
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    Measuring small resistances.

    My mum is in a hospice now so I have plenty of time sitting with her while she sleeps. @Touring_Rob have you ever seen this design? I’m going to recreate this, I have a LTZ1000ACH on the way from mouser and I have bought the other parts for the xdevs design of the LTZ1000 7.1V based reference...
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    Measuring small resistances.

    So as expected, the isolator didn’t work, I didn’t expect it to but it was worth discounting, I actually lost my previous isolator so needed another one anyway. I did look at the ADC results since I have no equipment here and I suspect it’s noise or ripple caused by the USB IP in the RP2040...
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    Measuring small resistances.

    as mentioned, the tolerance pages will be configurable, add as many as you want, they’re a convenience for checking a resistor is “in spec”. When it boots it goes straight into the measurement page, this shows the the measurement that’s under way, it also shows the average and minimum and...
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    Measuring small resistances.

    I've done a crap load on the UI overnight, back at my mothers because she really isn't very well so this is actually a welcome distraction. I also did a load of refactoring of the code, I'm gradually abstracting parts out, moving bits into their own classes since this is still running on a...
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    Measuring small resistances.

    So I've now started to actually start fleshing stuff out. I finally hooked up the rotary encoder, I also wired the "reset switch" on the back of the unit to TP6 on the rear of the pi pico board because the flashing is so f**king flakey with this crap "uf2" mass storage mechanism, it's no...
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