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Thread: Kudos to Bryan!

  1. #41
    TVWBB Honor Circle Bryan Mayland's Avatar
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    Keep plugging away at it, I'd love it if you would be able to figure out some new amazing noise-fixing circuitry or method or identify a new problem. Originally, the HeaterMeter circuit used 1M between TC- and GND but I found it to pick up a TON of noise and make a mess. I've tried on several occasions to raise the value back to where it probably should be at 1M, but it always ends in a noisy mess. I've also tried going down to 1k resistors on the TC+/- and upping the capacitors a decade to compensate but didn't see much difference. The Adafruit resistors are even one more decade lower with the same capacitors which should make their filtering even less effective!

    It could be the ferrite they have on the input power that is making a difference. There's no specs listed for it in the schematic so I'm not sure how to quantify its effects. I've tried creating a 3.3V "analog" rail as well with a separate linear regulator, inductors, ferrite beads, ferrite chokes, more capacitors, most seemed to make the noise worse. You could be on to something with the reference voltage though. If the reference voltage is more noise-immune than just the ground plane, it could act as a stabilizing force because any ground noise is just added to the output voltage in the HeaterMeter setup.
    I'm that HeaterMeter guy what ruins everybody's free time.

  2. #42
    TVWBB Guru Steve_M's Avatar
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    I plan to keep at it, though I'm going to spend some time figuring out Eagle or something to generate a PCB.

    On my DIY PCB, I've replicated the same 5v and 3.3v power config at the HM using extra components I already had on hand. I did this as I read the 3.3v supply on the wemos D1 mini wasn't too beefy, but in measuring the consumption of the TC amp, OLED and external ADC, the combined draw was under 10mA. Either way, nothing wrong with having a stable, dedicated 3.3v feed!

    I was really baffled last night when I discovered the instability when switching from the USB battery pack to a USB wall adapter to power the Wemos, which in turn powers the rest of the components on the breadboard. I've got another OKI-78SR-5 that I'll pop onto the breadboard and will see what happens with that. I also ordered a couple of AD8495 boards from aliexpress. They have a narrower/longer footprint than the more square adafruit board. I'm sure they'll arrive sometime in February!

    Again, Kudos to you. Getting all these lego pieces to fit together nicely is no small feat!

  3. #43
    TVWBB Guru Steve_M's Avatar
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    Using graph mode on my mooshimeter, here's what I'm seeing on the output of the TC amp.

    Wemos D1 connected with a USB battery pack:



    12v wall adapter to OKI-78SR-5 with 5v out into the 5v pin of the Wemos D1 mini:

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