The ground pins (Common Cathode) on a display are usually the center pins in the upper and lower rows of pins. Are there any markings on the unit and if there is have you tried to "google" the datasheet? I count 9 pins on your picture so perhaps this means dp,s,s,s,c,s,s,s,s. (decimal point, Segments, Common, Segments).
Cheers RH
EDIT
Seems like Cool has already found the answer
i found one just like cool's and another one too....i didn't understand cool's and image 1's diagrams though.image two is quite clearer but when it comes to cathode 1 & 2, it got me confused again x_X
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Razzler, cathode 1 (pin 14) refers to digit 1 (the left or tens) and cathode 2 (pin 13 ) refers to digit 2 (the right or units). Similarly , any anode no 1 refers to the anodes of digit 1 (tens) and any anode 2 refers to the anodes of digit 2 (units). So, for example pin 16 (A anode no. 1) is the anode to light up the top segment (a) in the tens digit. so if you use a 9 volt battery,a 470 or 560 ohm resistor and connect the negative to pin 14 and resistor and positive to pin 16 , the top bar (a) in the tens digit will light up.
+ve---Resistor---pin 16---(led bar a tens lights up)---pin14--- _ve
To display a whole numeric you will need a 7 segment display driver eg a 4511
Assuming of course that the datasheet you have applies to this dual segment display.
Cheers RH
I am desinging a display unit to read a counter (runs from 2 to 12) and a 7 bit register (value from 0 to 90). So am planning to use 2 Dual 7 segment display....the problem is how to decode 3 bit line from counter to one dual segment display n other 7 bit line frm register to another dual segement display..it wud be grt if u could mention the IC no too..
also regarding the common cathode and common anode types...does that mean ....+vcc is connected as common anode where as in common cathode it is shorted to the ground
you need a BCD-7 segment IC(7447)...i'm not too sure about the counters but i guess you can cascade decade counter(74192) and connecting it to the displays
use a multimeter to check the pins its easy. a data sheet may not necessarily be of the model of 7 segment that you have. i had the same problem with single 7 segements
13 and 14 are common. The rest are the LED. Just connect your positive to the 13 and 14 and ground the other pins to see the segments. I used 1 Volt and mapped out the pins.