Hey guys! I want to make a small project using a 4 x 7segments LED display like this with this pin configuration powered by an Arduino Uno. The problem is I need some ideas how to connect the display to a multiplexor then to arduino and what type of multiplexor should i use. The display is a recovered part from an old desk FM radio with clock. Thanks!
Step 1: Work out the pinout.
Use a 5V supply (say from the 5V of the Arduino) and a reasonably safe resistor (say 1K?) and probe around making a map of what segment lights up with what combination of connections. Remember, LEDs are polarised, so check each pair of connections in both directions. Yes, that means 2^21-21 possible combinations - over 2 million combinations. However it's not that many you will have to try. Once you have found a combination where one segment lights up, try keeping one connection still and moving the other - chances are one of the connections will be a common. Once you have, the rest is quick to discover.
Once you know what the connections are, and what combinations of elements there are, get back to us and we can better help you connect it to the UNO.
i've already done that but it's killing me inside...i'll try again tomorrow 
and about the resistor, i've did the test using a 270ohm resistor and everything was just fine. thanks for reply and i'll be back with news tomorrow 
cheers
Hi timofteandrei,
Looking at the pictures I count 30 edge solder points. This is possibly arranged as 4x 7 segments, 1x colon ( and 1x power or ground. What you need to do is determine if its a common anode or common cathode display. If you have a multimeter then set it to buzz/diode mode, touch a pin with plus and touch along the rest of the pins with minus. If nothing registers/buzzes then put minus on the pin you had plus connected to and try again. I would expect at least one pin to register something, if one does then this pin could be the common anode/cathode.