I am building a simple sensor device that's using Adafruit Fona to be connected to the Internet. I want to power up RFduino from the Fona USB 5v power supply. There is a pin on Fona that supplies 5 voltage as far as I understand and I am using voltage regulator to step it down to 3.3v There is a schematic:
The problem is: When Fona starts sending data over gprs RFduino gets rebooted. I guess there is a voltage drop or current spike or something. I've tried to put 100uF capacitors around the regulator, but it didn't really help. Although sometimes it works fine... but in most of the cases it does not.
How to fix the circuit that it works and stable?