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I'm having a surprisingly hard time figuring out which seven segment display I have on a board I'm looking at.

It is common anode, as there is one pin tied directly to Vcc.

It's like this, except rotated 90 degrees (the pins are vertical, along the sides):

enter image description here

Assuming pin 1 is in the top-left (at the f-a intersection), I know that the CA is at 3,8. But other than that I don't know which pin is which.

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  • \$\begingroup\$ What exactly is the question again? \$\endgroup\$ – Pyxzure Jan 29 '14 at 3:44
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    \$\begingroup\$ Does it really matter? You know the pinout, and the typical led specs are good enough unless it is a special high current version or anything. There are hundreds of thousand of 7 segment models, many of which are built to order and have no specs or data sheet available. \$\endgroup\$ – Passerby Jan 29 '14 at 3:47
  • \$\begingroup\$ @Passerby I'm reverse engineering a board. I don't know the pinout. I can figure it out with experimentation, but by looking at the picture, I don't know which direction I would rotate the pins. (In my configuration, is pin 1 at the f-a corner, or by DP?) It's not a big deal, I was just surprised that this was such an uncommon configuration. \$\endgroup\$ – Jonathon Reinhart Jan 29 '14 at 3:58
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    \$\begingroup\$ It's a really common pin configuration for 9.1mm displays. \$\endgroup\$ – Spehro Pefhany Jan 29 '14 at 4:05
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    \$\begingroup\$ He's probably asking where pin 1 is physically \$\endgroup\$ – Pyxzure Jan 29 '14 at 4:13
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For practical purposes, you will never find the datasheet for the 7 segment display you have. Especially of one that's used in a random device you are just trying to figure out. They are rarely off the shelf parts. They tend to be custom designed, or at the very list, a standard one is marked with a custom part number. The specs are under NDA. Unless you work for the company that ordered the parts, you won't find it.

That said, you can take first parts of the part number (if any is printed on the display), and look for similar ones. The pinouts are often identical or very similar. If no part number is listed, or you don't find anything, then you have to get your hands dirty. First, forget about a "standard" pinout. They don't exist.

Get a 3v coin cell battery. They have high internal resistance, so they can be used without resistors. Taking advantage of the Diode part of the LED which prevents current from flowing the wrong way, and the low voltage of a 3v coin cell, connect one side of the battery to one pin. Then connect the other side to every other pin, one by one. Have a note pad handy. You can make your own schematic that way.

The rest can be done by making a schematic of the board. Find the voltage source, find the inevitable resistors (with values if you can). Then use Ohm's law. I = V / R. By assuming 20mA and typical forward voltage drops for the color you see (~2v red, orange, ~3.2 green, blue, etc), you can figure out pretty much everything you need about it.

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  • \$\begingroup\$ I never realized that 7 segment displays were so "random" like this, and assumed they were more like ICs, etc. I was going to go about determining the pin-segment mapping by process of elimination when lit, but your button-cell approach will work great. Thanks. \$\endgroup\$ – Jonathon Reinhart Jan 29 '14 at 4:57
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Here is one very common configuration with vertical pins (9.1mm digit). Pin 1 is shown in the drawing; they are numbered like a DIP package (pin 10 is opposite pin 1).

enter image description here enter image description here

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