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

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