I have test boad with module SIM800C https://www.aliexpress.com/store/product/Free-Shipping-Smallest-SIM800L-GPRS-GSM-Module-MicroSIM-Card-Core-BOard-Quad-band-TTL-Serial-Port/2342338_32708504554.html?spm=2114.120106126.96.36.1990bed99qfIC1e
When I connect to module with PC and send AT-commands it work perfect :
ATI = SIM800 R14.18
AT+CGMR = Revision:1418B05SIM800C24_BT
AT+CSQ = 16,0
But after I enter SIM card to connector, module stop to answer to AT-commands and LED stopped to blink.
I checked with other module but it made same.
What to do ?
Probably too late, but might help someone else. At least I found this question trying to solve my exactly same problem.
It’s likely that you have power issues. The module is quite hungry for power in short bursts. So if you power it with the lab psu, or any other powerful (4V, 2A) source, the long wires between psu and the module will act as inductor, not allowing the quick surge of required amps.
Checking the voltage on the module with the oscilloscope, I see a short 200 uS dip in voltage from 4v down to 3.3v, and this likely causes SIM800 to brown out.
The solution in such case would be soldering an electrolytic capacitor (randomly picked 470uF) directly to the module’s VCC/GND pins. It fixed the problem immediately.