Hello,

I've just completed my first mbed project for work; it's a WAV file player based on external triggers, basically simulating a car starting, running, and stopping when connected to an external ignition switch. My design uses a few relays and plays WAV files via the AnalogOut pin capacitavely coupled to an audio amplifier IC.

The problem I have is when the power is first applied (I'm using an ATX PC power supply to drive the mbed with +5V) the audio output doesn't work. Only after manually pressing the RESET button on the mbed does the program work as intended. After the initial power-up and manual reset, everything works flawlessly until power is cut and re-applied.

Is there any software work around to this issue? The mbed is "embedded" in a larger hardware, and the reset button isn't readily available.

Thanks in advance for any help!

Jason

I have the same problem/question. After initial power up, how to run code without having to press the reset button?

Dave

First of: You could apply a reset button outside the hardware, by connecting a button between nR and GND.

But: It seems to be a bug, I could understand, if it were because you didn't push reset after downloading software to mbed, but it isn't. Weird.. Have you tried to check the firmware of the mbed? (i.e. opening the mbed link from mbed itself?)

Lerche

This problem may occur when the power supply does not have a propper rise time or have transient states and spikes. (especially with switch mode PS like atx ..)

Try putting close to the mbed supply pin a R-C group for filtering the spikes. (ex. 33ohms and 220uF/16v).

Another solution is to put a R-C group on the reset pin of the mbed, RC constant that is bigger that the time to reset mbed. This RC makes a redundant Power On Reset from the POR on mbed.

Titi