Until now my mbeding was strictly attached to pc while I played around with it. Now I have completed a project using a SPI TFT touch screen, as mentioned in cookbook. It works just fine while connected to mother but when I switch to battery power it wont do anything. Funnily enough I noticed that I was getting 5v on pin 40 and 3.3v on pin 39 which seems the wrong way around so I'll have to check my wiring (but it still works when connected to pc). When I've sorted this out will I need a bootloader when running off battery or will it start my code immediately ?

Hello, I think (correct me if not) that 5v on pin 40 and 3.3v on pin 39 is available only if mbed connected through mini USB connector to PC. So if You are powering mbed from battery, via Vin and GND pins there is no voltage on pins 39 and 40. So I think your LCD is not powered and can not display anything. I will be happy if this can help You. llumpu

Hi Gregory,

Little has identified the problem; when you are powered by USB, the 5v from USB is available on the VUSB out pin. When you are powering from VIN, it is not available; we only have 3.3v regulators on board.

In both cases, VOUT should be available at 3.3v to make it easy to power external circuitry.

Simon

There was indeed a wiring problem. Everything works fine now. Thanks for your interest

Hello, nice to hear that Your project works fine now. I also added some points to help with Your yesterday request about USB host and USB device.