Basic Questions

How do I match the UART level between modules and the MCU ?

a) If the UART level of the MCU is 3.3V, the following circuit is recommended. If the level is 3.0V, change the resistance value from 5.6K to 14K.

b) If the UART level of the MCU is 3V or 3.3V, the following circuit is recommended.

Note: Make sure that the minimum client upper limit is less than 2.8V minus the diode voltage drop.

c) If the UART level of the MCU is 5V, the following circuit is recommended.
How do I deal with modules separated from network in a test of electrostatic discharge ?

The network light and power light could be a good basis for judgment.

a) If the power light is on and the network light is flashing: the SIM card is not ready, which means that the SIM card will not work after electrostatic discharge. Please check the SIM card and improve the anti-interference ability.

b) If the power light is on, and the network light is on or normally on: The module is blocked, which is due to poor performance of the customer's PCB. If the power supply and GND loops are normal, please check the GND state, and if the surge protection is good, please check …. It is recommended to connect the TVS on the RESET pin of the module to GND.

c) If the power light is off: The module has surely been powered off, which is caused by the customer's power supply. Please improve the anti-interference ability of the power supply.
How do I connect the USB port of a module to a PC ?

Making the connection based on the following schematic diagram. ESD9M5.0ST5G or ESD9L5.0ST5G is recommended as the over-voltage protection TVS. Note: Please keep the USB port of the module for further upgrade and debugging.

PgUp 1 2 PgDn