SparkFun Satellite Transceiver Kit - Swarm M138 Hookup Guide
Contributors:
Ell C, 
PaulZC
PaulZC 
Current Draw
The peak current drawn by the modem, during message transmit, depends on the supply voltage:
| Supply Voltage | Sleep Current | Receive Current | Transmit Current |
|---|---|---|---|
| 3.3V | 80µA (Peak) | 26mA (Typ.), 40mA (Peak) | 850mA (Typ.), 1000mA (Peak) |
| 5.0V | 110µA (Peak) | 25mA (Typ.), 45mA (Peak) | 550mA (Typ.), 600mA (Peak) |
We strongly recommend powering the Breakout from 5.0V to reduce the peak current draw.
The TXO, RXI, TX/RX and GPIO1 signals remain 3.3V even when VIN is 5.0V. It is not possible to use 5.0V I/O under any circumstances. Doing so may damage your modem.
You can power the board directly from USB-C or USB 3 ports, but not older USB 2.0 ports. USB 2.0 (non-SuperSpeed) ports are limited to 500mA. You can still use our Breakout with USB 2.0, but you will need to connect additional power via the VIN and GND breakout pins.
On Raspberry Pi boards, the USB sockets are powered directly by the (USB) Power In connector. You can connect the Swarm Breakout to Raspberry Pi using USB provided that your power supply can deliver enough current for both the RPi and the Swarm M138 (during transmit). The official Raspberry Pi 5.1V 2.5A (12.5W) power adapter is a good choice.