Hello,
I hope someone can help me with this, I'm using a Siemens TC35 GSM modem and connecting it via USB to Serial converter to a laptop, it works fine and responds to the AT commands when not loaded with a SIM card, but, as soon as I add the SIM card, the status LED blinks for 5 or 6 times then goes OFF and the modem stops responding to any commands.
thank you
Bad SIM, No Antenna?
Suggest that you use a self powered USB Hub for your USB/Serial converter. Many laptops fail when you load the USB. Timing or power, I have no idea. Just just fail frequently.
Bradford
A GSM radio is likely to pull several amps, so it won't be drawing that from the USB
it works! thanks , it turned out that the power supply wasn't supplying enough current, replaced it with one that can supply 1A and all works fine, thank you :)