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From: bp@www.zefox.net
Newsgroups: sci.electronics.repair
Subject: Re: Waking up a serial port
Date: Sun, 16 Mar 2025 00:50:18 -0000 (UTC)
Organization: A noiseless patient Spider
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Jeff Liebermann <jeffl@cruzio.com> wrote:
> On Sat, 15 Mar 2025 17:30:03 -0000 (UTC), bp@www.zefox.net wrote:
> 
>>While looking around inside a 12 volt to 120 volt inverter charger
>>I noticed a pin header labeled "5v Rx Tx Gnd" near the edge of the
>>main circuit board. 
> 
> That sounds more like a USB-A connector pinout:
> <https://components101.com/sites/default/files/component_pin/USB-Type-A-Connector-Pinout.jpg>
> 
> See if there's any data on the Rx pin.
> USB data runs at 12 to 480 Mbits/sec.  What's the maker and model
> number of your oscilloscope?  What's the scope bandwidth?
> 
> If the connector is USB, the data is differential between the + and -
> pins (which may be the Rx and Tx pins).  RS-232 is specified at
> +/-15VDC.  It's possible for it to operate at 5VDC.
> 
> <https://www.testandmeasurementtips.com/measuring-universal-serial-bus-usb/>
> 
> The inverter manufacturers name and model number would also be
> helpful.  Good luck.
> 
> Begin Mini_Rant()
> 1.  What problem are you trying to solve?  (Keep it simple)
I'm trying to figure out if I can talk to the controller

> 2.  What do you have to work with?  (maker, model, versions, photos,
> URL's)
Owon vds1022i usb scope, 100Ms/sec, likely 10 MHz bandwidth. Board
images are at
zefox.net/~bp/ampinvt/2nd_inverter/board_photos
It sure doesn't look like a USB port to me. If it is, my scope is blind.

> 3.  What have you done so far and what happened?
Connect the 'scope, power cycle the inverter, look for traffic on Tx.

> 4.  What is your ability or experience level?
Retired experimental physicist, from the pre-digital epoch.

> 5.  Optional - All the background data and history.
The inverter behaved strangely (but usably) when acquired. Eventually
I replaced it with another unit and would like to understand what ails
this one if it isn't too difficult. It's still usable as a spare, so
I'd rather not damage it. 

My working guess is that the software is misconfigured. The vendor's
behavior was completely obfuscatory (if that's a word) so I'm not asking
them for anything. Their products are sold cheaply enough that buying
three to get two that work was still the best deal available.

> End Mini_Rant()

Thanks for writing,

bob prohaska