DFR SIM7000E and Adafruit Metro M4 Express Airlift

Hi,

I'm having trouble getting these two boards to work together:

 

- When I stack the SIM7000 on top of the Metro M4 (as intended), the M4 won't boot properly or show up as CIRCUITPY drive on the PC, when connected per USB. No serial connection is established. Arduino IDE won't find the board either.

 

- If I don't stack and wire the SIM7000 manually, the M4 will show up as CIRCUITPY and I can use Mu editor or Arduino IDE. But no output on the serial console.

Pin config:

M4 VIN (12V)/GND -→ SIM7000 VIN/GND

M4 RX/D0 -→ SIM7000 D8 (or D0)

M4 TX/D1 -→ SIM7000 D7 (or D1)

 

Are they not compatible?

 

Thanks!