I'm trying to connect a SIM800L to my nrf52840-dk which I power through 5V USB. I'm a beginner at electronics so just want to make sure I understand how to wire things, please advice. My plan so far:
If I understand the sim800L spec sheet correctly, it will need its own power source because it requires 3.5~4.2V and 2A, which is too high for the nrf52840. So my plan was to connect the nrf52840dk 5V output to a lm2596 buck converter module that will convert that 5v down to 4V and then connect the converter to the SIM800L's VCC. I will then wire the nrf52840dk and SIM800L grounds together.
For UART communication, it looks like the SIM800L requires 2.8V which is lower than the nrf52840's 3.3V. For the nRF52840’s TX line (3.3V) to the SIM800L’s RX (2.8V), I am not sure what to use... maybe a resistor divider? I believe fro the nRF52840’s RX line (3.3V) to the SIM800L’s TX (2.8V) can be wired directly since nrf52840 will detect it correctly. I know that the nrf52840 GPIO level can be configured but the board already has some GPIO pins that need to use 3.3V. Can pins be configured individually (e.g. one pin uses 3.3V and another one uses 2.8V)? That would save me the trouble of doing a resistor divider or other solution.
Thanks for the help?