04-10-2017, 10:59 PM
Hey Mark, thanks for your help the other night! You got me unstuck when I was pulling my hair out - much appreciated.
I'm not sure blaming the power supplies is the right answer here. I'm measuring roughly 0.3A drawn - it's not taxing any of these power supplies, nor the connector. A quick google says brand-name Micro USB connectors are rated for 1.8A for VCC and GND, and even the crap chinese ones must be good for half that.
I don't think ripple is a problem either - or it'd be causing crashes much more often than just at boot. My board has run 24 hours without a crash (until I shut it down), once it made it through booting.
So, my working theory is that at some point in the boot, a bunch of hardware is switched on at once, causing a short/sharp sag in the voltage. (Why it doesn't cause a problem with an HDMI monitor, I don't know, timing issue?) That's the sort of thing I've seen fixed with a decoupling capacitor, storing a wee bit of energy locally, rather than in the power supply filter caps at the far end of that - probably thin - wire.
Your PI filter undoubtedly works, but I'm not sure it's necessary. A single capacitor on a connector on the Euler bus is smaller and easier to add than circumventing the entire power input connector and filters. I think I'll try the biggest ceramic I can find first and see what happens. Might also see if I can get the o'scope to capture a voltage drop. But... tomorrow.
I'm not sure blaming the power supplies is the right answer here. I'm measuring roughly 0.3A drawn - it's not taxing any of these power supplies, nor the connector. A quick google says brand-name Micro USB connectors are rated for 1.8A for VCC and GND, and even the crap chinese ones must be good for half that.
I don't think ripple is a problem either - or it'd be causing crashes much more often than just at boot. My board has run 24 hours without a crash (until I shut it down), once it made it through booting.
So, my working theory is that at some point in the boot, a bunch of hardware is switched on at once, causing a short/sharp sag in the voltage. (Why it doesn't cause a problem with an HDMI monitor, I don't know, timing issue?) That's the sort of thing I've seen fixed with a decoupling capacitor, storing a wee bit of energy locally, rather than in the power supply filter caps at the far end of that - probably thin - wire.
Your PI filter undoubtedly works, but I'm not sure it's necessary. A single capacitor on a connector on the Euler bus is smaller and easier to add than circumventing the entire power input connector and filters. I think I'll try the biggest ceramic I can find first and see what happens. Might also see if I can get the o'scope to capture a voltage drop. But... tomorrow.