I need help on how to connect a two digit display to my Adafruit ItsyBitsy 32U4. The display has 10 pins. I want to use it to read out the entry from a four button membrane board.
The display is probably wired with the first 8-pins used for the seven numeric segments plus the decimal,point, and the remaining two pins are the common digit substrate (two digits)...
The first thing you need to determine is whether the displays are ‘common cathode’ or ‘common anode’.
This determines how you’re going to ‘drive’ the digits & segments.
With a common CATHODE display, you need to pull the ‘digit pin’ for the required digit LOW, and the segment pins (common to both digits) to the driven + voltage... (anode positive - cathode negative)
This is the fundamental principle of multiplexing... you quickly alternate the digit pins low (-), and depending on the characters to be displayed, you’ll set those segment pins on (+) or off for each digit.
This all happens very fast, so both digits appear to be on all the time (persistence of vision), while they are in fact flickering alternately with their own individual digit displays.
With a ‘common anode’ display, the voltages are reversed... segments are (-), while the digit pins are (+).
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Fine description 
Just note that the common pins deserve driver transistors for the high current of up to 8 illuminated segments.
You can reverse engineer this. I googled "determine 7 segment pin out", this plum:
If that's what you problem is.
"Though if it was not a standard part, probing with a 1K resistor in series with a 5V supply is fast and easy and will verify functionality."
Don't forget the series resistor…
HTH
a7
Thank you so much for the information. I purchased some two digit displays that have 10 pins. I am brand new to this and this is way over may head. I was hoping to find a tutorial with a display that shows the 10 pins on back of the display and what wires to connect them to the Arduino. I have found some with single digit displays and some that are very vague on how to do this. Does anyone have any information on what pins on the display need to be connected to the corresponding pins on the Arduino? I don't have any knowledge of how to attain the information I have. I also don't know what would be the first pins. Is it from the top or bottom? Left or right? If someone can help I would appreciate it.
There's a trick to making the most of the advice we give, and that is to actually read it.
The link @alto777 supplied in Reply #4 speaks to exactly your situation, offers a competent discussion of the problem and reveals several avenues of approach.
A 1K resistor, a 5 volt power supply and whatever y'all call "elbow grease" these days. Oh, and a pencil and paper.
a7
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Thank you again for your response. I did actually read the information. Thank you so much for it. I have a 2 digit display with 10 pins. The information I see is for a single digit display which I have numerous examples on how to connect. I am completely new to this and have no knowledge on the "elbow grease" or "calculations" I need to perform. I was inquiring to see if someone had a pin readout of how to connect this display. It is a CL3621BH display. I don't pretend to have knowledge on how to do this. I don't mean to offend by asking a question. If I am missing something, and you are willing to guide me, please show me what I am missing. I have read over this several times and cannot figure out how to do this. If you are not willing to help, I do understand. Thank you for your consideration.
No offense, sry if I implied any was taken.
The technique from the link is general. Looking for 8 anodes and 2 cathodes (or vice versa) is very much the same - you know what you need to find: the pair of pins used for each segment of your display. Many tests of pairs of pins and creating a map as you go.
Each pair must be probed twice with the current (probes) reversed so you are sure to illuminate the segments, which are after all diodes.
I recommend you give it your best try. It turns out to be necessary in this case, see below, but it is a useful technique. Getting empirical is part of this business, especially if one is using cheap parts w/ sketchy or non-existent documentation.
OR you could just google the part number… always worth a try. And for future reference, it never hurts to take a few extra minutes when you bring your problem forward at the onset to supply all the information you have. The part number for example, which by your original post one might infer was unknown to you.
I googled your part number and quickly turned up a diagram.
You must be older than I!
Pro tip: google TF out of anything you can read on a part.
a7
To push you along, those are COMMON ANODE (CA) displays with pins 5 and 10 the anodes (+) for the two separate digits.
The other pins are the eight segment cathodes - common across the two digits).*
If you put +5V on pin 5 or 10, and 0V/ground through a resistor 330R - 1K ohms, you can wipe that across the other pins, and you’ll see the segments light up in one digit to
rutgers other (pins 5 & 10)…
If you didn’t find the block diagram on google, just sketch the pin numbers down on a bit of paper.
- as a CA display, you need to switch between the digits +v high side, while presenting the required segment/display bits on the low side 0v.
(Read up on seven segment displays... a single, double or multiple character display is exactly the same - just more digit pins)
It sounds tricky, but there are a lot of code examples to do this - even without any external parts than the segment ‘current limiting’ resistors.
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