[sdiy] 5V power supply for logic and uC

[John Speth]

> I'm planning a number of modules that will need a 5V supply to power
logic
> ICs and microcontrollers from the 12V rail of a Doepfer modular.
> What I'd like to know is what measures I should take to protect the rest
of
> the modular from noise. What I'd do at this stage is just add a 7805
voltage
> regulator with the standard caps from input and output to GND.
> Is this a recommended approach or is there a problem with this?

I think the answer will be "That depends" (always the case, isn't it?).

You'll need to know how much current your 5V circuits will draw (worst
case, sleep mode, average, duty cycles, etc).  You'll also need to know
the how loaded you're 12V supply is with and without the 7805.  I think
the frequencies at which your digital circuit operates will also dictate
how you isolate it (ferrite beads, caps, layout).  Finally the logic
itself is probably a big consideration.  For example, TTL logic will be
noisier than a modern highly integrated high quality MCU.

Our experienced EEs can certainly add specific information on the numerous
things to deal with the cases you'll come up with.

JJS