I would love some more detail, thanks. Here are my questions:
- What baud rate did you use?
- Did you point the updater at the RAR file or a file inside the expanded folder? If the latter, which folder?
- Did you use the broken out TX and RX pins on the board (presumably after removing the jumpers), which are on the 3.3V side of the UART level shifter, or did you use UART pins on the SIM900 itself?
- What did you use to turn the board on, the PWRKEY switch, a jumper from pin 1 to GND, or something else?
- What sequence did you use? I.e. did you start the firmware update first, then turn the board on, or did you turn the board on first, then start the firmware update?
(I have tried almost every combination of these that I can think of, except that I haven’t tried all of them with every single baud rate. Still out of luck.)