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My friend (for some reason unbeknown to me) decided to take an alarm clock apart. He thought that the seven segment display would be of use to me, so he gave it to me. However, before I start hacking away, I need to know whether it is common anode or common cathode, preferably without destroying it! I have done the obvious thing; checking if a datasheet exists, and unfortunately one doesn't. Do you guys have any ideas?

Well, if you have an electrical meter, as I am sure you do, if you connect the common ground wire to one of the leads; be it the anode or cathode, and the other test wire to another lead, if you get a resistance of near 0, the cathode is the one connected to the common ground, and the anode is connected to the other wire. If, on the other hand, you get an extremely high resistance, the common ground wire is connected to the anode, and the usually red wire is connected to the cathode. Hopefully this helps to some degree! I could be way off...
Mateo, I'll have a go now, thank you Smile The only issue I have is that none of the pins are labelled. Still, we'll see.
ElectronicsGeek wrote:
Mateo, I'll have a go now, thank you Smile The only issue I have is that none of the pins are labelled. Still, we'll see.


Sounds good! Not having the pins labeled sounds like a real issue; perhaps you could send a small current through different combinations in order to determine which is which. As long as it is low enough, it shouldn't blow out the diodes. Kind of brut-force, but it could work. Usually the one of the center leads tends to be the anode. Good luck! Smile
Many multimeters include "diode tester" functions, which can be a bit nicer for these sorts of tasks (you can determine the forward voltage, at any rate).

http://www.allaboutcircuits.com/vol_3/chpt_3/2.html
*bump* Did you make any progress on this? It shouldn't be too terrible to figure out, given that the display doesn't look horribly complex. Smile
Looks like the process of elimination might be the only sure way out of this one without a datasheet. I'm guessing there are 7 pins representing all possible segments, plus 4 pins for common rails; but who knows how the colon and AM/PM/Alarm LEDs are wired?
KermMartian wrote:
*bump* Did you make any progress on this? It shouldn't be too terrible to figure out, given that the display doesn't look horribly complex. Smile


I'm afraid not. I stuck my meter into diode tester mode and had very little luck. I'll have another poke about later on this week. Smile

I have to say, it would be great to get this working, because I can have a play with some shift-registers and learn how to use them and I can put my newfound C skills to good use on my Arduino in the form of a fun little project.
  
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