CubeCell - Vext usage

Hello everyone,
I’d like to use an external ultrasonic sensor (Maxbotix MB7389, TTL output, 3v3, peak current 49mA) with CubeCell. It would read the sensor, transmit via LoRa and then go to sleep for 2 minutes. This would include shutting off the sensor to save power.

Can I use the Vext pin to power on the ultrasonic sensor and then shut down again before going to sleep?
Which pin would you suggest to use for TTL?

best regards, Martin

You are using the Dev-Board?

TTL means data input/output via UART?

Yes, I am using the dev-board.
I had a working prototype using an arduino pro mini. I used the library softwareserialread to read the sensor (TTL or RSR232, both is supported by the sensor). I basically would like to do the same here.