5v and 3.3v component combination..

My project is using an arduino mega board as well as a number of 3.3v components which when all running at full pelt could draw in excess of 200ma, the arduino mega will also power a 320x240 tft
and 4(currently) 5v relay boards in addition to sensors and llc boards to allow 5 to 3.3v comms

So for the real project i want a PSU, I have bought a 12v 25w switching psu which i intend to box up with the 240v a/c switching relays and step down voltage boards and connect to the arduino project box with a multicore flex.

The plan is to use a dc-dc step down converter board (ebay) based on a LM2596 with a pot to tune down the output to 5v, and then use a LM117 board to step that 5v down to 3.3v.

I also want to supply 12v to the project box to run fans when internal temp sensors indicate it necessary.

so can i use 1 x +12v feed off the 12v psu, 1 x +5v feed off the LM2569, and 1 x +3.v3 off theLM117 and use a common ground from the 12v PSU to supply the power to my project?? or should i take the common ground off the last dc converter in the chain the LM117?, or should i belt n braces connect all three grounds?

I would rather check first than fry all my boards and watch the magic smoke dissipate..

thanks in advance

I would take a separate ground wire from each module back to the 0v ground of the 12v psu; known as the 'star' method.

Hi,

I would take a separate ground wire from each module back to the 0v ground of the 12v psu.

Yes! That becomes the "Common Ground Point".. Also make sure that point connects to the building ground as directly as possible.

See THIS: about relay connections and optical isolation...

Thanks gents, that i shall wire all gnds up to one.. I just had a pause while finally boxing up the long awaited bits from china for the psu side, and as i only ordered 1x of each ....

the relays i am using are 4 x individual boarded modules akin to the 4x module in the link above :wink:

@terryking228 are you suggesting i connect the -ve DC voltage from the PSU to the AC Mains earth? surely i risk frying everything if anything on the same mains ring shorts out on the earth?

the ac/dc psu has 5 x terminals Live, Neutral, Earth, -ve DC, +ve DC.