Power Supply

hi there,
I like to power an EMX board via my Dirve Electronic with 3,3 and 5V but the EMX is not really willing to boot. All that is powered by a PC Power supply
are there an tricks or things I have to look at

thanks to your input


Hi Rene

“Dirve Electronic” didn’t come up in any obvious searching, can you explain further?

Can you also tell us exactly what EMX based board you have? Is it a Cobra, or a Spider, or some other board?

These devices will require a reasonably stable power supply so whatever power you feed them will need to be able to supply a few hundred milliamps minimum (assuming no other peripherals connected). How are your 5v and 3.3v lines being converted?

And finally, for now, how do you know the device is not willing to boot? What check are you doing at that point to know it hasn’t started?

a couple L293 to drive 12V DC motors

But evenn that electronic disconnected and the EMX connected to the 3.3 and 5V of the PC Power suplly does not make the EMX boot.


what board do you have?
how do you know the device is not willing to boot? What check are you doing at that point to know it hasn’t started?

So what we know is you have the 5v and 3v3 lines of the ATX power supply connected to the EMX (somehow?). I would first think that a PC power supply, particularly for the 3v3 line, will not be a good power source on it’s own. You really need to be putting a higher voltage output from the ATX supply into a regulator of some kind, with appropriate capacitors.

Should be a perfect on, ATX Power a switching PWR supply and sofar I know extremly good signal quality

I feed these lines into connector one on the EMX board the same as the USB client would come in
if i connect everything the voltage is 3,22 and 4,98V so that should work.
but the EMX (spider board) just gives a white screen

That way of suppliing the boad should be no different to the batterypack


there is a little programm showing me a image if booted. so

with the USB Client DP it works and with the direct supply from the ATX power supply not


then I’m sorry, it’s probably time to use a different power supply.

You really cannot guarantee what an ATX power supply will do; they’re notoriously noisy. I’d suggest you just route 12v power from the ATX supply into the DP module. It has appropriate 5v and 3v3 regulators and circuitry to provide what you need.

But digging deeper (it’s taken a while to get good details out of you; you help us help you by providing as much detail as you can)… How do you connect the 5v/3v3/GND to the Spider? What wires and what connector back to the Spider? Want to take a picture of it and share it here so we can see?

How about you make the simplest app you can, that starts and flashes the debugging LED for ever, and deploy that without the screen attached, and see if that shows the same or a different behaviour?

I tending to being unwilliing to believe it is the ATX supply

I am using an experimental board on it a extender connected to Connector 1 on the Spider

On the experimental board 3,3V, 5; 12V are available with patchcables to the extender

I think i can say it does not make much sense if u have a ciurcte where all power is available, when u start fumblinmg around with DP and his external connector, not a very nice solution. I must be somehow possible to start the EMX with direct 5 and 3.3V.
I messured everthing current and voltage in both conditions

With the DP and the ATX
all the same but with the ATX it does not not want to boot. LED on the EMX is on connector on

PIN 3 and PIN 7 with 1ok to 3,3V does not change anything

is there anything to be observed if u are using a BAT Pack