Comment on Digital buffer works for a bit, then stops, turning it off for an hour resets it to working again
avidamoeba@lemmy.ca 2 weeks ago
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.
avidamoeba@lemmy.ca 2 weeks ago
Retested with a brand new TI IC and an external battery. It died again. Perhaps the issues are coming through the input/output lines. I finally threw in the towel and implemented it using a Trinket M0. Seems to work for now. Will do more testing.
litchralee@sh.itjust.works 2 weeks ago
(sorry for the long delay)
From your description, I’m wondering if the internal pull-up from the bike computer might actually be an active output, and that the open-drain buffer is causing the bike computer to give up sourcing that pull-up voltage. That is to say, if a larger-than-expected current is drawn from the bike computer, it might trigger a protection mechanism to avoid damage to its output circuitry.
To that end, I would imagine that either: 1) an inline resistor to limit drain current, 2) a push-pull buffer, or 3) both, would help rectify the issue.
My suspicion is based purely on the fact that getting stuck low for an open-drain device could be an issue “upstream”. If it were stuck high, I wouldn’t normally suspect this path.
avidamoeba@lemmy.ca 2 weeks ago
No prob whatsoever. I appreciate your time.
As for the computer, I have no idea and I’m not skilled enough to check. I ordered some push-pull quad channel buffers from TI and Nexperia, SOIC breakout board and decoupling caps. Unfortunately I made it work using a Trinket M0 with a trivial CircuitPython program. Already tested it on a bike ride and just sitting powered on over 24 hours. No failure so far, so I conformally coated it and installed it. The fly was killed with a bazooka. 😂 And so I think I’m gonna keep it like that and will revisit the new buffer ICs I bought if it fails again, or if I need to build another adapter. Thank you for your help!
litchralee@sh.itjust.works 2 weeks ago
BTW, you might consider posting about your finished results at !micromobility@lemmy.world . We enjoy all things bicycle-related there, especially when it’s solving a unique problem or solving it in unique ways.