Can't download sketches via USB-serial converter onto 644P, even with a bootloader

Thanks for sticking around tho, I really appreciate your efforts in trying to work out the problem. It's crazy cuz in this case the issue couldn't be found in the schematic and can very easily be glanced over. On hindsight, I can read 8mhz on the crystal in my photo! Insane. Oh, and my Rx/tx LEDs work perfectly now. Everything works as I intended. Phew.

Darn you are right! Then I really didn't look closely enough, I'm sorry, I should have noticed. Sorry! in my defense I have to say that I took more care of the UART connections and the CH340G, whether everything is OK there. Unfortunately, I have not checked the values of the two crystals in the photos. only in the schematic.

I guess my celebration was a bit too early because it stopped working again :frowning: I haven't changed anything...

Alright, so I desoldered the CH340G chip and replaced it with a new one. It works now. I pray to God, PLEASE to not give my circuit any more issues... This is REALLY weird since I have no idea when and how the chip got damaged. When it stopped working again after my little crystal switcheroo "solved" the problem, I ran a loopback test on the CH340G by isolating it from the 644P by cutting off all RX/TX connections, then wiring the RX and TX together. The test didn't work, which led me to think the CH340G was probably fried. I replaced it with a new one, and it's now working again. For now, at least... :crossed_fingers::crossed_fingers::crossed_fingers:

OK, you really seem to have had bad luck with the CH3040G. Perhaps the chip broke at some point during the troubleshooting process, which took some time and perhaps a lot of experiments.
I have already killed one or the other component while looking for errors like this, although I cannot understand WHY the component dies in that situation.

Rant, rant...

I'm going to study electrical engineering in college and I wonder how many F's I will get for simple mistakes like this one lol.

If your EE labs are like the labs I had, you won't get the opportunity to make such mistakes. A lab that requires that you build a circuit with a 16MHz crystal will supply you with a parts kit containing a 16MHz Crystal. It's depressing.

That does mean that the experience you're getting now "fooling around" on your own, will put you "ahead" of your classmates when it comes to debugging circuits, at least if they're trying to get by with just classroom learning.

(my university contacts assure me that labs have "improved" in the 40y since I graduated. But those are like "the Dean of Engineering", and I don't know how good a view they have of how things are going "at ground level.")

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