nrf9160 feather USB to UART

Lord-Lucan

Hi,

I’ve been wondering about the USB to UART transceiver when the feather is on battery only. Forgive me if I’m barking up the wrong tree as I haven’t had a prod with a scope yet to see if I’m mistaken.

When powered by battery only it looks to me like the lines from the nrf9160 are still being driven (the UART_TX) when the USB to UART (CP2102N) is powered off. If this is the case this is probably undesirable.
There seems to be no way to detect from nrf9160 IO if the feather is on battery or UART. That may be a nice to know as you can have a low power and high power mode in your application. May be able to infer something from the battery level pin. But a logic level would be nice to have 🙂

Regards,
Paul

jaredwolff

Lord-Lucan points well taken!!

Normally I would recommend for folks to disable the debug UART during deployments. That way there’s no extra power draw from those pins.

Additionally, you could check the RX pin to see if it’s high. It will go low when the CP2102 is no longer powered. I haven’t tested it but that was my solution when I thought about this problem previously. If there were extra GPIOs I would have added a dedicated detection pin. Maybe they’ll make a newer nRF91 with more pins in the future 😄

Thanks
Jared