a have a Arduino pro mini (compatible) Board connected to a SIM800c module via Pin2/3 by using Software Serial. After some huddles with String-Variables the project works now perfectly when arduino is connected via USB to my PC an (normal) 5V Circuit is power on tool (because SIM800c needs more Power for sending)
But when i disconnect USB from PC the Serial Connection to SIM800C doesnt work work well. Unfortunally - i'm a little bit blind without Serial prints.
Anybody can help me? can it be an electrical problem (Add Info: connect the USB to a powerbank doesnt work too)
Thanks for any tip