Comment on Digital buffer works for a bit, then stops, turning it off for an hour resets it to working again

litchralee@sh.itjust.works ⁨2⁩ ⁨days⁩ ago

• avidamoeba@lemmy.ca ⁨2⁩ ⁨days⁩ ago

  The output is stuck at low.

  The input keeps alternating high/low. I’ve checked by disconnecting it and then measuring it. I’ve also checked by substituting the source for identical brand and model spare unit.

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  • litchralee@sh.itjust.works ⁨1⁩ ⁨day⁩ ago

    For your edit #2, can you post a schematic of the relevant part of the circuit? It’s a bit hard to imagine how things are arranged, especially where your pull up resistor at the output of the buffer is.

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    • avidamoeba@lemmy.ca ⁨7⁩ ⁨hours⁩ ago

      Image

      This is my attempt at a diagram of it. There’s 3 connectors, bike computer PAS, Bafang PAS torque sensor, DC barrel (battery). There’s a Recom DC-DC with built-in wire leads. There’s a breakout board on which I’ve soldered the buffer. All lines are short, thin wires, 1-4cm in length. As far as I know, there’s a pull-up resistors inside the bike computer on its inputs. I can see the values going high when I disconnect the cable from it (there’s debug screen on the computer that shows the input values). When assembled it becomes a part of a cable. I’m using heavy duty heat shrink tubing for structure. I have one of these working on another bike without issues for a while now. The components in the adapter are the same, but the bike motor and controller are slightly different, so there could be differences in what noise there’s in the system.

      Yesterday I replaced the Nexperia IC for a TI which I had on hand, no capacitors still (on order). The TI worked well during a test for an hour. Then it stopped working at LOW, just like the Nexperia. Is it possible for these events to be damaging the IC? I feel like the new chips last a little longer, then they stop working much faster after recovery.

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  • litchralee@sh.itjust.works ⁨2⁩ ⁨days⁩ ago

    If I had to guess, perhaps the buffer circuit is going onto latch-up due to ESD spikes, which is then locking the open drain to conduct, which is why you’re seeing a LOW output.

    When in doubt, I suppose you can tack on more decoupling capacitors nearby the buffer’s Vcc.

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    • avidamoeba@lemmy.ca ⁨2⁩ ⁨days⁩ ago

      As an idiot, do I wire capacitors in parallel to Vcc and GND of the buffer? What value?

      Also I have the same kind of buffer from TI. Is there any sense to change the IC and see if the TI fares better?

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      • bitfucker@programming.dev ⁨20⁩ ⁨hours⁩ ago

        Yes, sounds about right. For general purpose decoupling that is a good value. Make sure to place it as close to the IC as possible. A longer path will add more “noise” to the system. Do read more about the capacitor type too since it can matter a lot. I suggest looking at Phil’s Lab video on YouTube to learn more about this stuff

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