Trouble connecting with USB UART

[don]

I'm having trouble connecting to my LoPy and FiPy. I didn't buy the expansion board so I'm trying to use the Adafruit FTDI board. http://adafru.it/284

I've wired the board based on the documentation. https://docs.pycom.io/chapter/gettingstarted/connection/lopy.html#diy

If I connect using screen, I don't see any text in the terminal, but the pycom light turns green when I type.

$ screen /dev/ttyUSB1 115200

I see the same behavior with the LoPy and the FiPy. I've tried swapping out the Adafruit FTDI board with a Inland FTDI board and got the same results.

I am able to connect to both devices using WiFi.

I tried to update the firmware but ran into similar problems. When I start the update I see "Connecting to the device to get its information." After 30 to 60 seconds I get "Something failed trying to connect to the device" or some other error.

Am I missing some wiring? Can I update the firmware over WiFi? Other suggestions on what to try next?

Thanks

[nathanh]

@don I think you need to move your TX/RX pins down 1 spot on your LoPy, look at https://docs.pycom.io/chapter/datasheets/downloads/lopy-pinout.pdf

[robert-hh]

@don Besides the comment of @nathanh , you should check the levels of Tx and Rx. If the USB/UART bridge is set to 5V, the output levels of Tx and RX might be at that level too, being not healthy for the Lopy. At least you should insert a current limiting resistor of about 4.7 kOhm.
You might also set the USB/UART to 3.3V, but the internal regulator may not be able to deliver sufficient current for the LoPy.

[don]

@nathanh that was exactly the problem. Thanks for the link to the correct pinout.

@robert-hh the Adafruit FTDI board defaults to 5V VCC and 3.3V logic.

I'll see if I can work with pycom to get the diagrams fixed in the getting started docs.

[seb]

@don

Fixed

[don]

@seb Thanks!