Core 2 with Sim 800 module.

  • Is the M5Stack SIM800 module compatible with the Core 2?

    I just connected and I have noticed the Red Port A has stopped working.
    Any advice appreciated, thank you.

  • Hello @pipy71

    looking at the GSM SIM800L pin map or schematic I can see that GPIO5 is used as reset (RST). On M5Core2 GPIO5 was replaced with GPIO33 which is also used for SCL (I2C) on M5Core2 Red Port A. That is why it stopped working.

    In other words the GSM SIM800L module is not fully compatible with M5Core2. It can only be used if you disable the external I2C on the Red Port A.

    I've made a comparison list of all the GPIO changes between M5Stack and M5Core2. You can find it here.


  • Thank you!

  • This seems to be pretty common. Not all modules are compatible with all cores. I wish they would advertise which modules work with which cores.

  • @ksprayberry
    I agree with you. I bought a Fire and a Core2 with two Lora modules, in the Fire it fits perfectly and in the Core2 it does not. Now it will force me to buy another Fire if I want to use another type of module. I have not been able to use them.

    I don't think it's a good policy, in the same brand, not to make everything compatible. This is my personal opinion


  • Hello guys

    I just got a GSM SIM800L module and have it working with M5Core2 by changing RX2 from GPIO16 to GPIO13 and TX2 from GPIO17 to GPIO14.

    What I stated before about GPIO5 being used for RST turned out to be only half the truth. Sorry about that. By default RST is unconnected, but a solder bridge can be made to connect RST to GPIO5 in case the application needs to reset the module.

    Happy Stacking!

  • Hello @felmue. I have a problem with connecting SIM800L(M004) with Core 2 . When I try to turn Core on it just light build in LED for second and turn it off. Core did not start, but when i give 5v from another power supply to SIM800L it starts properly. Did you have problem like that?

  • Hello @BrandPlay

    does your M5Core2 turn on ok w/o the SIM800L stacked to it?

    If you are using the M5Core2 battery, it is fully charged?

    If you power your M5Core2 from USB, have you tried a different cable / power source?