Well, here is a strange issue that I can’t seem to figure out:
I have a bluetooth module attached to the EXT header pins. I am using the 3.3V power on the header to power the bluetooth device. I have until now always had power coming from the USB device port. Bluetooth module works great.
Today I removed the USB and attached a 7v supply to the external power jack for the first time. Now my Bluetooth module will not power on. I can measure 3.3v at the header so I know there is power to it, but it simply will not work. Bad module you say? Well, I reattached the USB power and it works fine.
One theory is that there is not enough current to satisfy the bluetooth module with the external power jack. How could that be? My supply is a programmable power supply set to 7v and has plenty of current. The bluetooth module only needs 100ma @ 3.3v to initialize.
Could I have a bad LM1117MP-5? That is only difference I can see in the path power takes between USB vs. External Power.
The board itself appears to function fine regardless of power supply.
Any other theories? Its got to be a simple (humbling) explaination.