Raspberry PI - help with reading inputs plz

[al_notts]

Hello all,

Just registered on here as could do with some help is poss. please....

I've finally decided to get my raspberry PI out that I've had for around 18m and hardly touched due to time constraints etc etc.

I want to read an input from a 240v transformer (like an old mobile phone charger), transformed down to say 3v or 12v. I appreciate I'd need to match the input voltage to one that can be read by the Rpi (3.3v?) but I'm not sure how I make the circuit through the Ras Pi inputs. If I connect the positive wire from the charger on the DV side to one of the inputs on the PI, I assume I'd have to connect the negative wire of the charger to somewhere too? I appreciate that I could do this by using a relay instead by totally separating the two supplies although I don't have one at the moment. Can I hence avoid having to use one please?

Any help would be v. much appreciated. Thanks in advance,

Al_Notts

[Pauldf]

We could do with a bit more info on what you are trying to achieve.
The pi can provide enough voltage to be used via a switch to operate an input. Or are you wanting to read the DC voltage value from the charger (the pi inputs are digital so without some sort of interface it wont measure analogue signals)