Guru
Joined: 21/06/2018
Location: AustraliaPosts: 1156
| Posted: 03:22pm 07 Jun 2024 |
Looks like Morgs67 & Poida wins the prize - thanks fellas I just had to get to the answer my way by a process of elimination. The curly part was the noise of the 5V regulator that was posted and it looked terrible combined with the fact that I was seeing activity on the USBtx data LED I wanted to see if it was the USB IC outputting crap or the processor.
The reset for the USB IC is via a capacitor from the Nano uC so putting a reset device on the Nano uC does not preclude the USB IC from still outputting crap (if it was the culprit) I do know voltage supervisors well having first used them over 35 years ago.
The voltage monitor did fix it though and only 1 is required for the Nano on the controller. The only TO92 supervisor part I had in stock is an S8054HN an old Seiko part with open drain reset, active low and around 4V trip point. I put one on the Nano and fully tested the voltages from 0V - 5V and everything is as dead as a dodo until greater than ~ 4.1V where it comes to life and no amount of slow twiddling between 1 & 2.5V resulted in any LED activity. Return to 5V all working fine. So stomping on the data line in reset stopped crap from upsetting the LCD Nano.
A really lucky outcome is that the part can be mounted under the PCB and a 1-1 connection for 3 pins on the nano socket solder side so very easy to retrofit and putting it on the main PCB then 1 part is not required to be fitted to each nano module. The only bad news is the part is ~ $1.20 from Digikey there may be cheaper sources ie Farnell and really any part with threshold voltage from 3.5V - 4.3V would all be fine. I prefer open drain but there are open collector parts with very low power consumption that should be fine also.
I would recommend the S-80838CNY-B2-U which has a threshold of 3.8V and is closest to the tested S8054, but there are other similar choices.
The Nano on the controller that crashed last night when playing with low voltage around the 2V threshold appears to be badly bricked. It refused to program, the message was something like "cant find serial port or no device inserted". I tried reinstating a new bootloader but it wont have a bar of that either. If I request device ID it responds as usual with the same answer as a good one but apart from that its broken.
Any ideas what went wrong or how to fix it? I suspect a random fuse burnt unintentionally but which one and how to clear it - its not the $3 cost but I am sure its a simple fix and curious what caused it.
Edited 2024-06-08 01:32 by wiseguy