this post was submitted on 17 Mar 2025
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high voltages on usb to TTY UART? (lemmy.one)
submitted 3 weeks ago* (last edited 2 weeks ago) by [email protected] to c/[email protected]
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Hi, Any1 have experience with this usb to TTL 6 pin converters? I just want to know if I have a dodgy one that I bought from Ali or normal behaviour.

Doesnt seem right. I have it plugged to a powerbank, following voltages read from pinout, without any jumper link.

5v = 5.3 Vcc = 3.9v 3.3 = 3.2v Tx RX = 3.9v

If I use jumper link from 5v to VCC, then tx RX = 5.3v, if I jumper link VCC and 3.3, RX and tx = 3.9v.

Thanks for reading

Photo of product http://0x0.st/81fc.jpg

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[–] [email protected] 1 points 3 weeks ago (2 children)

The 5.3V is from your computer, that's not the fault of the USB UART.

3.2V is perfectly acceptable for a 3.3V rail.

The 3.9V is a bit weird. Can you post a photo of your USB UART board? Maybe the main chip has an inbuilt 3.3V regulator separate to the external one.

[–] [email protected] 1 points 2 weeks ago (1 children)
[–] [email protected] 1 points 2 weeks ago* (last edited 2 weeks ago)

That's a CH340G, it has an in-built 3.3V regulator. But there is no external regulator on the board.

Maybe the chip is running off its internal 3.3V, but the board designers put a tie-up resistor on one of its pins to 5V, which results in the weird 3.9V. Dunno. Try attaching a 1K resistor between that pin a GND, see if that makes the problem disappear.