I just teared down a cheap alarm clock I had lying around that I wasn't using to play around with. There's one thing I don't understand though.. from what I can understand, there's a power converter to convert AC to DC and there are 3 wires coming out of it.. 2 yellow and 1 red. Since I don't have a voltmeter (I'm not very well equipped) I don't see how I could determine which is negative and which is positive and I couldn't find an answer on the net Should this be easy to find or is there a secret rule of wire coloring that I don't know?
Well, I don't recognize that wiring scheme, but you want to be careful. AC power has three leads. DC usually only uses two wires (in most circumstances I've seen). So it's possible you're dealing with live mains current.
Clocks frequently have an AC power adapter, because getting your timing from the 60Hz (or 50Hz) is very accurate over the long term. So you could be seeing all three leads from a plain center-tapped transformer, or you could be seeing some DC power supply with an extra lead that still has the AC signal on it...
aye in all they are relativity simple devices get the cycles per second from the wall plug after it has been stepped down to a reasonable voltage and count it
I would suggest that before doing anything with mains current you should equipped. A multimeter costs very little these days and it might just save your life!
In places like the USA where the mains frequency is 60Hz I have heard that many cheaper wall clocks derive their timing from that.
Be very careful when working with mains voltages and anything attached to that if you don't know what you are doing.
The "module with three wires coming out" is it a transformer. Google a transformer to see.
If it is a just a transformer with no rectifier then the three wires are possibly a tapped output. Meaning that the overall output voltage is divded, so that like the transformer in this rectifier circuit:
If its a transformer and rectifier combined then the output will be DC and its most likely a dual polarity power supply. ie a postive voltage, referenced to a ground and a negative voltage referenced to the same ground.
However it could be that the transformer isnt being used to generate a dual supply and that the extra tapping is just used to provide a low voltage 60Hz AC for timing to the IC and the rest of the circuit is powered of DC. Too many variables and difficult to speculate without seeing the circuit itself.
Why not post some pics of the internals and the PCB and we can see...
Don't worry, I won't put my fingers on it while it's plugged
Also, I can't take pictures right now my girlfriend is in vacation with the camera..
But there's one thing I don't like now.. I have cut off the display from the PCB and it fitted pefectly on a breadboard. Now I though to control each pin with Arduino I could just plug some 74HC595 shift registers so it wouldn't use a lot of wires, until I realised that not all the output pins are on the same side! Why did it have to be like that? Is there anything I can do that will work without turning my tiny breadboard into a wire jungle? I've got 20 input pins for the display and they are all spaced just like on a breadboard.
your not really saving wires, each pin is still going to be connected, but it gets thinned down on the arduino side to 3 or 4 pins
also the 595's have 7 out of 8 outputs on one side of the chip so it should be easy to jumper on a breadboard. A forest of wires is common, but if you do the loopy kind of jumping its pretty easy to trace with a pencil tip