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Joined: Sat Sep 16, 2023 8:54 pm

USB alternative for UART to GPIO 14/15/18

Sat Sep 16, 2023 9:09 pm


I have a MakerFocus UPSPACK v3 (https://www.makerfocus.com/products/ras ... wer-supply). To talk to it, you normally put GPIO14 to TX, GPIO15 to RX and GPIO18 to STA. It then runs at 9600baud. This works fine. But I needed to move over to USB. Thinking that this is TTL, I bought a FT232RL (https://www.amazon.com/gp/product/B09C2P4XTF). I can see the ttyUSBx on my RPi4, but when I connect the yellow FT (RX) to RX on the UPS board, and green FT (TX) to TX on the UPS board, nothing happens. (I can type in the terminal and eventually garbage comes back to me). Is the STA/PCM_CLK pin absolutely necessary in this case, or is it extra?

Am I missing something else somewhere?

Thanks, Tuc

Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 5326
Joined: Mon Sep 29, 2014 1:07 pm
Location: Cambridge

Re: USB alternative for UART to GPIO 14/15/18

Mon Sep 18, 2023 10:10 am

Although the Amazon product page says to connect the red wire to 5V, I think it's actually a voltage reference (the UART itself gets its power from the USB lead) - try connecting it to 3V3.

The STA pin is actually used to deliver a pulse to request a shutdown. The software resources include a Python script to monitor it and initiate the power-off.

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