I have developed a very simple module board based on SIM7000G to be used in the LAB of the company to make fast PoCs (proof-of-concepts), I know the schematic and layout of this board is very far from something very good or "ideal", but anyway I want to give a try. Below is the link for the schematic in PDF.
https://www.mediafire.com/file/3mwr9wiqpg3ped9/Modulo-SIM7000-v03.pdf/file
I'm stuck in the basic UART test, it is not working. I'm testing on the protoboard. Basically what I do is:
(1) The board is supplied (SIM7000G VBAT signal) with 4.2V. At this point, the signal SIM-TX (pin 9 of SIM7000G) is fixed at level '0', and it is known that the inactive level of UART is level '1'. This is probably because the module is not yet initialized.
(2) 4.2V is connected to signal PWRKEY (before the resistor of the transistor) for more than 1 second, using a wire, to initialize the SIM7000G. At this point, the power supply that is set to 4.2V and supplying the board shows a rise of consumption going to up to ~80mA, then after a small period the consumption reduces to less than 10mA from the power supply. The signal SIM-TX (pin 9 of SIM7000G) is fixed at level '1' now (1.8V). The module initialization "seems" to be ok, due this change from '0' to '1' on SIM-TX (pin 9 of SIM7000G). A pull-down was also added to PWRKEY signal.
(3) I do connect the PC to a USB-to-serial converter and attach it to the signals ESP-RX and ESP-TX of the pin header, plus the GND.
(4) On PC, when I send "AT\r\n" to SIM7000G, I can observe a very good signal on pin 10 (RXD) of SIM7000G, for example the '0' bits of the bytes presents a voltage very close to 0V, with well defined edges. This measurement was done with the probe of the scope connected directly to pin 10 (RXD) of SIM7000G, what means that it is receiving the bytes from the PC on its RXD pin.
(5) Here is the problem, the signal SIM-TX (SIM7000G) keeps always fixed at level '1' (1.8V), I verified this with scope and logic analyzer directly on the pin of SIM7000G module (pin 9, TXD). Signal SIM-TX keeps always in '1', that is, it does not answer to the "AT\r\n" sent by the PC, because I observe that SIM-TX pin logic level never changes.
I have tested with multiple baud rates, 9600bps, 115200bps, and intermediate baud rates, without sucess. And with 3 boards (different SIM7000G modules). STATUS pin is going to level 1 after PWRKEY initialization.
Regards.
