[Arduino, PWM, analog meter] my fancy contraption freezes intermittently :( - Page 1
Forum section: electronics / beginners

author: faekjarz
author_rank: Regular Contributor
timestamp: March 11, 2017, 04:58:28 pm
content: Hey there enginerds!I made a fancy contraption and documented the first beta versionhere in the forum…it fails intermittently, i.e. the bloody ting doesn't twitch its needles anymore.Here is what it looks like on the back side:…directly connected, through 22k resistors.I run it on Linux. Its CH340 USB to serial IC is the only device of its kind handled by the kernel, so it's always /dev/ttyUSB0.I noticed two failure modes with varying severityttyUSB0 just disappears and my, admittedly rather crude, script throws errors. In this case i stop the script, unplug, wait a few seconds, re-plug, restart, donettyUSB0 remains existing, the RX LED of the Arduino (nano v3 clone) still indicates incoming data (changes of duty cycle), but the needles don't move anymore.In second case i made a weird observation: originally i tried to blind-fumble the reset switch on the back side, i felt the connection points under my finger tip, where i soldered the meter to the board …viola, without actually closing the reset switch, it started moving its needles again. My layman's guess is, that there is some kind of capacitive or static charge thing going on. Something that prevents the systems' desired operation, but is neutralised by connecting my body (skin) to those contacts, which causes it to operate as intended again.What phenomenon did i witness?And what does it teach me (us) regarding improvement of the system reliability?

author: Nusa
author_rank: Super Contributor
timestamp: March 11, 2017, 05:20:09 pm
content: Or you've got a poor solder joint on one of those wires, and mechanical force from your finger made it work again, at least for the moment. You could try reflowing them all and see if the problem goes away.

author: faekjarz
author_rank: Regular Contributor
timestamp: March 24, 2017, 02:06:21 am
content: Quote from: Nusa on March 11, 2017, 05:20:09 pmHmm, that might actually be the cause. Well, kind of; I "made it work again", and left it (the whole system, metre, cables, USB connections) untouched for over a week. It still works. I doubt that a cold joint is the culprit here. All solder joints look fairly decent. Might be a broken wire though, but intensely wiggling those didn't affect operation. Another parameter I've changed is the USB port, the contraption is connected to. I'm still using that one cheap arse Chinesium USB cable, which proved unreliable when wiggled in the USB 2.0 host port of my PC. Wiggling it in an USB 3.0 port doesn't disturb operation at all. So, that USB 2.0 host port could be of lesser quality, rather than the cheap Chinesium pokey bit. Wiggling the pokey bit in the Arduinos' mini-USB receptacle, quite fiercely, didn't affect operation, at all.The mentioned unreliable USB 2.0 host port is part of the front i/o panel of a CoolerMaster Elite 130 Mini-ITX case.Initially i thought, the CH340 USB-tty-IC of the Arduino Nano v3 (clone) is unstable; it's (seemingly) not -> worked fine all the time …on the USB 3.0 port …in 2.0 mode, of course.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: March 24, 2017, 06:30:41 am
content: I had a similar intermittent problem with stuff I connected to the front-panel USB ports on my computer case. Finally I took it apart and looked carefully at the solder joints connecting the USB connectors (and audio, mic jacks) to the underlying PCB that mounted to the case. They were slightly cracked from the mechanical movement caused by plugging and unplugging cables from the connector. Cheap brittle lead-free solder cannae take the strain of repeated mechanical stress cycles! So I re-soldered everything with good old leaded solder and voila, no more problems.I don't know if this is happening with your case USB connectors but it might be worth taking a look.