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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. Similar results when plugged directly into the Wemos.


    I still need to A/B the output from the Adafruit TC vs the HM TC
    Last edited by Steve_M; 10-23-2018 at 09:08 PM.

  4. #44
    TVWBB Guru Steve_M's Avatar
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    I've also been looking at the software side of things. I added this little function to see how fast things were running. Yes, I do realize that the process of timing the loop will inherently increase the time to complete a loop


    Code:
    void trackloop() {
      if ( now - prevLoopMillis >= 1000) {
        currLoops = numLoops;
        numLoops = 0;
        prevLoopMillis = now;
      }
      numLoops++;
    }

    At first I was getting the result of ~85 loops/second ( 85Hz ). Pretty brutal considering the ESP8266 has an 80MHz processor.

    Reducing the thermocouple read + NIST calc routine to once every 5ms changed the loops per second by around 19,000, thats almost 225% gain in efficiency. I also had some delay(1) calls that seemed to be needed to keep the watchdog timer from getting upset but a single yield() placed in the middle of loop looks to be doing the trick and that increased loops/sec by about 500.

    I'm sure there are some more efficiencies to be made, but I'm pretty happy with the results so far.

  5. #45
    TVWBB Guru Steve_M's Avatar
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    My thoughts while killing time on my train ride to work.

    I think the main issue is the low voltage output from the AD8495 and even though the DC noise is minimal, since the output is already so low, it just gets amplified. My hypothesis is that the 1.25v reference voltage on the Adafruit board masks the noise better as a couple of mV of noise won’t be seen when you’re already starting out with 1250 mV before the TC amp adds to it.

    Next hypothesis. If I use something like the ADR510 1.0 shunt regulator to add -1.0v as a reference voltage to the AD8495 my output will always be between -1.0v and 0v (0v being 200C) which allows me to use the 4x gain multiplier on the ADS1115 which operates in the range of -/+ 1.024v
    Last edited by Steve_M; 10-24-2018 at 03:48 PM. Reason: missing words

  6. #46
    TVWBB Honor Circle Bryan Mayland's Avatar
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    I'm not sure noise works like that, it should be an AC signal on whatever DC bias is there, be it 0V, 1.25V or -1.0V. What I think it is providing is filtering that attenuates the noise. I'm not sure though, all this analog stuff is like magic to me, and I mean the kind of magic that never works right!

    You could also try a capacitance multiplier to power the AD8495/ADC. They're used to smooth out higher voltage power supplies (usually mains frequency) but I don't see why they can't be employed for lower voltages stuff too. The concept is the same as the low pass filter we have on the HeaterMeter probe lines, except they can't supply any power because the 100k resistor will only pass so much current (33uA at 3.3V). To boost that, a simple NPN transistor is used to amplify the current, effectively "multiplying" the size of the capacitor by the hFE of the transistor (~100x for a 2N2222). Here you can see a quick demo I threw together in the Java Circuit Simulator showing 5V input with a 1V 1kHz noise signal on it and the corresponding smoothed output with even the most modest 1k/1uF low pass filter. The 1k resistor on the output is just to simulate a load, but you'd put another capacitor on the output just like there would be if this were a voltage regulator.


    I'd say try it with a 10k resistor, a 100uF capacitor and 0.1uF in parallel (low ESR is key), and a 2N2222 or any NPN you have on hand and see what you get?
    I'm that HeaterMeter guy what ruins everybody's free time.

  7. #47
    TVWBB Guru Steve_M's Avatar
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    I had a feeling I was somewhat wrong in my assumptions. I'm not an EE and I certainly don't pretend to play one on TV!

    I'll see if I can give the capacitance multiplier a try. Thanks for the info.

  8. #48
    TVWBB Guru Steve_M's Avatar
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    This project has remained in its status quo for some time now, mostly because I'm making delicious coffee and if it aint broke, don't fix it!

    Last weekend I scored another Gaggia Classic (same make / model as the one I have) for dirt cheap and am going through the process of making it PID controlled as well.

    Last night I wired up a solid state relay and a new K type thermocouple to the boiler and connected it to my the pre-existing wemos + ads1115 controller setup I've been using all this time thinking this should be a simple swap, but no! I started seeing the input temps bounce around on the new machine, where things were nice and stable on the old machine. So what gives?

    After a bit of tinkering around, I tried connecting the aluminum boiler (which has the thermocouple screwed into it) to the same DC ground as the rest of the circuit and voila, the noise went away. Making sure this wasn't a fluke, I removed and added the ground back a few times and every single time I grounded the boiler the noise went away and temps stabilized.

    I wonder what's different between these 2 thermocouples. They're both generic k type thermocouples with an m4 screw head that are commonly used with 3D printers.
    Last edited by Steve_M; 01-21-2019 at 12:26 PM.

  9. #49
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    Maybe one TC is isolated and the other isn't?
    I created the Roto Damper, RD3, HMv4.2 sliding back case, "air-burner" and the "ping-pong" valve in my quest for delicious "set and forget" BBQ.

  10. #50
    TVWBB Guru Steve_M's Avatar
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    Quote Originally Posted by RalphTrimble View Post
    Maybe one TC is isolated and the other isn't?
    Yeah, that looks to be the case. I continuity tested the first one ( QIDI Technology Thermocouple ) and neither of the wires appear to be connected to the brass m4 threaded connector.

    This is the new one, and while the look the same, they clearly aren't. This grounded style is obviously affected by the SSR pulsing the current through the heating element of the boiler.

    Neither of the listings shows them as being isolated or grounded.
    Last edited by Steve_M; 01-21-2019 at 04:51 PM.

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