one supply = two supplies

Maybe two diodes could seperate them? Other than that only transformer isolation remains, which is a lot more complicated.

Google "DC-to-DC-converter module" DC-to-DC converters are available as modules with four terminals, two for input power source and two for the output. The output is generally "electrically isolated" from the input, our name for your "two different supplies" requirement.

Inside the dc-dc converter module will be a switching circuit that creates an AC signal to drive a transformer. A rectifier converts the transformer's AC back to DC. Items to evaluate in choosing a DC-to-DC-converter, besides voltage and current ratings, include: the switching-frequency, an output-noise spec (switching activity makes electrical noise), current-limiting short-circuit protection, and voltage regulation (some converters simply provide an output proportional to the input, with some effective output resistance).

Here are a few links,

And here's a (long) link to 716 in-stock modules at DigiKey.

In the event you need lots of power, that's available too,

The simple way to do it is to just use 2 supplies.

Luhan

Yeah- the simplest way is to find out what the hell you're doing *for real* instead of latching on to some fantasy about isolated supplies. Your dialer is alarm system compatible and does not require isolation. Maybe learn the concept of something called *polarity* on the alarm output and GSM input ports so that the GNDs match. You don't like this answer? Go to basics.

It may be that there is some high frequency interaction between the two devices through the power supply feeds. Try putting a large inductor (100mH or more) in series with the feeds to each device fed from one supply, and decouple each to ground with a capacitor.

Slurp

First, I'd diagnose what is causing the circuit to malfunction when the devices have a common power supply and ground - if merely using a separate supply clears the malfunction, then there is some kind of wiring error.

Good Luck! Rich

The OP apparently wants to stick something like this in a vehicle. He should be aware that attaching anything to a vehicle battery is applying 'the power supply from hell' to quote a LTC app note. He would be better off just buying power supplies designed to plug into the cigar/ette lighter socket which will at least provide clean power. Alfatronix makes a nice range of them.

I currently design for the automotive market and it's quite a challenge to meet the requirements for droop and load dump (ISO 7367) [in the EU we also have to get what's known as an 'E' mark for anything connected directly to a vehicle battery].

Cheers

PeteS

Duh - that should be ISO 7637 (low caffeine typo)

Cheers

PeteS

S'okay- nobody reads your pedestrian limey sh_t anyway...

how amusing - A Sunday driveby insult, and not that good either :)

"how amusing"- aren't you the suave and sophisticated *pimp*- not real impressed with your very *British* petty posing and arrogance- GFOAD.

On a scale of 1 to 10, how much of a D*****ad is Fred?

Vote now, vote often!

Luhan

Can't rate Fred yet.

We need to establish a "D*****ad" Standard first.

If that standard were Phil Allison, then Fred would barely move the needle ;-)

...Jim Thompson

I guess I should have simply asked for 'nominations' for 'least appreciated newsgroup poster'.

"The Envelope Please!"

Luhan

Dictionary categorizes "d*****ad" as vulgar slang. They got that right, you are vulgar:-)

More of your irrelevance- try Least Effective Poster and you take it hands down.

In which case my answer had the desired response. Bad hair day? Or are you giving up caffeine cold turkey? (A friend of mine once gave up smoking wild turkey - told me it was the only way).

Cheers

PeteS

PS. Have a nice day, as they say all over the states.

Your answer "had" a response? And "wild turkey?" Who smokes "wild turkey" anyway? What part of the bird do they smoke exactly? You don't even speak English.