Hello all,
I have a SIM808 Shield from DFrobot which works fine, I can use it with my Arduino Uno or with my USB-Uart Modul and communicate with it without any problems. So all good, I seem to understand how the SIM808 works with the AT commands.
However, when using another SIM808 modul from "and-global.com" which is under the name "BK-808" (Gsm Gps Sim808 Breakout Board, Sim808 Core Board mit Gsm und Gps Anten), I have huge troubles. I only get garbage data on the terminal.
Even if I check with the oscilloscope, the BK-808 outputs only garbage data in an infinity loop. Simple commands like AT are not working, no response to my command and only garbage in a continuous stream. I tried different baud rates, new cables, new BK-808 modules ( I have 3 ) but none of them seems to work.
Does anyone have an idea what the problem is?
INTERESTINGLY: After some time, I notice the blue LED blinking up and the Telephone number of the inserted SIM becomes accessible. So this means that the SIM modul booted up and registered the sim card. It reacts to my phone call as I see an increase in the current.
(I use a lab power supply with enough current(4A)
But still only garbage on the serial terminal. I attached a screenshot of the oscilloscope.
It seems to me that the garbage output could be the GPS Output Stream NMEA which comes out continously.
Example of the output stream:
'?' ':' ']' 'U' 'p' ' ' '
'?' ':' 'Z' 'U' '?' '?' 'i' '?'
As said, I tried different baudrates, parity bit, decodings... and of course there is a common GROUND connection between the BK-808 and my USB -UART modul or my arduino.
But why is it not readable and why is there no reaction to my AT command ?
Thank you and have a good day