3 ms·

Seems like a missed opportunity to try adding a capacitor dead-bug style onto the board to see if it cleans it up.

by oakwhiz 5mo ago

dragontamer 5mo ago
If it's really 20MHz++ noise that's screwing him, you need something faster than a through hole capacitor IMO to deal with it. That being said, I'm not 100% convinced this is a 20MHz++ noise issue.
- sebcat 5mo ago
  It's an easy test though and it can be an SMD component and some PUR-coated magnet wire or 30 awg single stranded kynar hookup wire. Use a small amount of glue from a hot glue gun to fixate it when done, or epoxy if that's your thing. Avoid cyanoacrylate. Not always needed but I imagine a drone moves around alot. Bodge wiring is a good skill to acquire - PCBs will not always be perfect. Maybe practice on something else first?
  - dragontamer 5mo ago
    True. I have a bunch of through-hole parts for these sorts of situations. There are plenty of small through-hole ceramics that have leads if you really want to go there. https://www.digikey.com/en/products/detail/vishay-beyschlag-draloric-bc-components/K104K15X7RF5TL2/286538 https://www.digikey.com/en/products/detail/vishay-beyschlag-... Like this or something similar.
    - jacquesm 5mo ago
      I've seen piggy backed decoupling caps straddling chips on some pretty fancy hardware. This lesson is re-learned quite frequently ;)
- WarmWash 5mo ago
  The capacitor doesn't have a concept of "fast enough", it's a passive component. The signal is what determines what it does when it encounters the capacitor. Non-linearities and capacitor species aside, a good ole x7r 100nF would clean this up. In general you can just liberally dump 100nF caps all over your pcb power traces and quash most problems like this before even knowing they exist. I joke that you make a circuit then take out your 100nF salt shaker to make it just right.
  - dragontamer 5mo ago
    Look up parasitic inductance. Through hole parts cap out at maybe low MHz. Many electrolytic caps frankly cannot effectively decouple signals above 100s of kHz even. Above that value, capacitors become inductors due to lead lengths, parasitic resistance, and other details. To make capacitors work faster, we make them smaller and smaller. Surface Mount Caps are the only way to reach 20MHz++ decoupling speeds, and you need crazier tricks if you need additional decoupling beyond that frequency.
    - WarmWash 5mo ago
      Yes, but we are splitting hairs at that point. The transient spike is a high impedance voltage that is tripping the high impedance internal protection circuitry of the magnetometer. So whether we have 20mOhms of capacitive decoupling or 500mOhms of inductive decoupling, both are better than the infinite impedance of nothing there. We're not building a precision filter, were cutting the paws off of a paper tiger. No need to let perfect be the enemy of good.
      - dragontamer 5mo ago
        This is a circuit with a switching regulator that is, presumably, stabilized with something on the order of a 10uH inductor + 22uF capacitor. So from my perspective, increasing the capacitance from 22uF on that output line to 22.1uF with a 100nF cap will likely do jack diddly shit. It is far more likely that, ex, the author of this post screwed up the regulator design. Ex: did the author mistakenly think that more capacitance is better-er and stick a 100uF cap there, blowing out the phase margin of the feedback of the switching regulator? Was the inductor properly sized? Not just inductance but also saturation current and internal resistance?
- ErroneousBosh 5mo ago
  > If it's really 20MHz++ noise that's screwing him, you need something faster than a through hole capacitor IMO to deal with it. That's always worked well enough in the past.
  - dragontamer 5mo ago
    That's because you weren't dealing with 20MHz noise. Hobbyists are not dealing with 20MHz noise issues. Period. And if you are actually crazy enough to deal with high frequency circuits like that, you would well know that the land of through hole designs is simply insufficient, and that you are probably somewhere with some 0402 capacitors and some tweezers right now.
    - jacquesm 5mo ago
      > Hobbyists are not dealing with 20MHz noise issues. It happens. Not often, but it does happen and it depends on the hobbyist and what they're up to (but you won't be sticking that together on a breadboard). Also: if you start using HCT, AHC or even G parts where you don't really need them it can happen to you in places where you don't normally expect it. Those things have crazy fast rise times.
      - dragontamer 5mo ago
        Real talk: 6 layer oshpark is cheap enough for a hobbyist and there are a bunch of 500MHz / DDR2 parts that can be laid out. Like 0.8mm pitch BGAs can fit and breakout. So yeah. Hobbyists can go here. But here be dragons!! Nonetheless, I continue to assert that typical hobbyists are making mistakes at 100kHz region rather than the 100MHz region.
        jacquesm 5mo ago
        That's fair. It's just that I have seen some hobbyists doing the most insane stuff and eventually getting it to work. Some HAMs for instance have pretty extreme skills and it is not their profession, they just do it because they like it, not because they get paid. And in many of those cases their skills are hard capped by their budget for test gear and simulation software rather than by their actual ability. Keep in mind that until not that long ago anything above 1 G was fair game because 'nobody does anything there anyway' and so HAMs and radio astronomers were pretty much the only ones with experience in that region.
- PunchyHamster 5mo ago
  you can dead bug SMD caps

Seems like a missed opportunity to try adding a capacitor dead-bug style onto the board to see if it cleans it up.

by oakwhiz 5mo ago

Seems like a missed opportunity to try adding a capacitor dead-bug style onto the board to see if it cleans it up.

If it's really 20MHz++ noise that's screwing him, you need something faster than a through hole capacitor IMO to deal with it. That being said, I'm not 100% convinced this is a 20MHz++ noise issue.

sebcat 5mo ago
It's an easy test though and it can be an SMD component and some PUR-coated magnet wire or 30 awg single stranded kynar hookup wire. Use a small amount of glue from a hot glue gun to fixate it when done, or epoxy if that's your thing. Avoid cyanoacrylate. Not always needed but I imagine a drone moves around alot. Bodge wiring is a good skill to acquire - PCBs will not always be perfect. Maybe practice on something else first?
- dragontamer 5mo ago
  True. I have a bunch of through-hole parts for these sorts of situations. There are plenty of small through-hole ceramics that have leads if you really want to go there. https://www.digikey.com/en/products/detail/vishay-beyschlag-draloric-bc-components/K104K15X7RF5TL2/286538 https://www.digikey.com/en/products/detail/vishay-beyschlag-... Like this or something similar.
  - jacquesm 5mo ago
    I've seen piggy backed decoupling caps straddling chips on some pretty fancy hardware. This lesson is re-learned quite frequently ;)
WarmWash 5mo ago
The capacitor doesn't have a concept of "fast enough", it's a passive component. The signal is what determines what it does when it encounters the capacitor. Non-linearities and capacitor species aside, a good ole x7r 100nF would clean this up. In general you can just liberally dump 100nF caps all over your pcb power traces and quash most problems like this before even knowing they exist. I joke that you make a circuit then take out your 100nF salt shaker to make it just right.
- dragontamer 5mo ago
  Look up parasitic inductance. Through hole parts cap out at maybe low MHz. Many electrolytic caps frankly cannot effectively decouple signals above 100s of kHz even. Above that value, capacitors become inductors due to lead lengths, parasitic resistance, and other details. To make capacitors work faster, we make them smaller and smaller. Surface Mount Caps are the only way to reach 20MHz++ decoupling speeds, and you need crazier tricks if you need additional decoupling beyond that frequency.
  - WarmWash 5mo ago
    Yes, but we are splitting hairs at that point. The transient spike is a high impedance voltage that is tripping the high impedance internal protection circuitry of the magnetometer. So whether we have 20mOhms of capacitive decoupling or 500mOhms of inductive decoupling, both are better than the infinite impedance of nothing there. We're not building a precision filter, were cutting the paws off of a paper tiger. No need to let perfect be the enemy of good.
    - dragontamer 5mo ago
      This is a circuit with a switching regulator that is, presumably, stabilized with something on the order of a 10uH inductor + 22uF capacitor. So from my perspective, increasing the capacitance from 22uF on that output line to 22.1uF with a 100nF cap will likely do jack diddly shit. It is far more likely that, ex, the author of this post screwed up the regulator design. Ex: did the author mistakenly think that more capacitance is better-er and stick a 100uF cap there, blowing out the phase margin of the feedback of the switching regulator? Was the inductor properly sized? Not just inductance but also saturation current and internal resistance?
ErroneousBosh 5mo ago
> If it's really 20MHz++ noise that's screwing him, you need something faster than a through hole capacitor IMO to deal with it. That's always worked well enough in the past.
- dragontamer 5mo ago
  That's because you weren't dealing with 20MHz noise. Hobbyists are not dealing with 20MHz noise issues. Period. And if you are actually crazy enough to deal with high frequency circuits like that, you would well know that the land of through hole designs is simply insufficient, and that you are probably somewhere with some 0402 capacitors and some tweezers right now.
  - jacquesm 5mo ago
    > Hobbyists are not dealing with 20MHz noise issues. It happens. Not often, but it does happen and it depends on the hobbyist and what they're up to (but you won't be sticking that together on a breadboard). Also: if you start using HCT, AHC or even G parts where you don't really need them it can happen to you in places where you don't normally expect it. Those things have crazy fast rise times.
    - dragontamer 5mo ago
      Real talk: 6 layer oshpark is cheap enough for a hobbyist and there are a bunch of 500MHz / DDR2 parts that can be laid out. Like 0.8mm pitch BGAs can fit and breakout. So yeah. Hobbyists can go here. But here be dragons!! Nonetheless, I continue to assert that typical hobbyists are making mistakes at 100kHz region rather than the 100MHz region.
      - jacquesm 5mo ago
        That's fair. It's just that I have seen some hobbyists doing the most insane stuff and eventually getting it to work. Some HAMs for instance have pretty extreme skills and it is not their profession, they just do it because they like it, not because they get paid. And in many of those cases their skills are hard capped by their budget for test gear and simulation software rather than by their actual ability. Keep in mind that until not that long ago anything above 1 G was fair game because 'nobody does anything there anyway' and so HAMs and radio astronomers were pretty much the only ones with experience in that region.
PunchyHamster 5mo ago
you can dead bug SMD caps