Just had a question for the masses. Just a bit of background story to kick it off. The face panel on our electric range broke a couple weeks back (physically, not electronically) and we had it replaced. The tech left the old one with us and I took it as a great opportunity to practice my desoldering skills. As I was removing components for later use, I decided I wanted to give the seven-segment display a shot. This would have been my first time doing one, and I'm finding plenty of excellent material on how to operate a multiplex'd seven seg, but I had a question. To kick it off here are some pictures of it.
Front View of the display.
The only form of label I can find....
The back of the display
So here is my dilemma from the datasheets I've been reading you have a "digit select pin" and a "segment select pin" I've even seen some models that have a digit pin for their colon/apostrophe/dot and when you select it some of the segment pins will turn on a specific dot. The problem I'm currently having is that since I've salvaged it off of an old board, I don't know what the model number is to find the datasheet to find out what pins are what.
I've tried google searches several times and am having trouble turning anything up, but I am new to this and was curious if anyone here knew of any resources for finding datasheets for the odd part like this or if you had any advice. I'm tempted to try probing the pins using some low voltage DC after trying to decipher the traces on the back of the display, but I'm more afraid to damage the thing.
By the way, I'm more than happy to take this post over to the multiplexing and leds forum, I figured that since this is the "device hacking" forum you guys might have some insight into how this thing ticks.
So while I was putzing around looking at datasheets for similar displays I almost always noticed one thing.
The segment pins always have a current limiting resistor on them to prevent the LED from frying.
So I grabbed the PCB that I pulled this display out of and found out this. All segment pin holes are highlighted red, with a tail pointing to the component I traced that is evidence of the pin type. All digit select pins are green.
This however, causes a bit of a problem for me, as you can see, I have EIGHT segment pins and only 4 Digit Pins. I was hoping that there would be five digit pins so as to select the "dot" digit and light either the colon, period, or asterisk. So that means that the asterisk must be selected by some other means? Maybe a certain voltage to the "dot segment pin"?
This oven display does use more than the colon, when selecting bake, you find that the degrees symbol lights up.
Well, food for thought I guess.
Edit: One other thing that I noticed. There are test points in the upper left of this PCB that has a ground test point and a 3.3v test point, so I would assume that the board as a whole is operating on a 3.3V DC current.
have you tried good old trial and error? make sure to use current limiting resistors everywhere and there really is not much which can go wrong.
Use a 220, 270 ohm resistor and probe away! You won't hurt anything. If you can read the segment resistors (or measure one) then use that value.
If you can't read what T12,13,14,15 are, then you to probe around anyway to determine if you have common anode or common cathode digits, and to figure out what is needed to turn the "decimal points" on.
Connect one of the common pins to Gnd, touch the resistor from +5 to the segments.
No lights? Flip things around.
I'm not getting any hits on "ai-ndqg01 datasheet".
Is there any different marking on the back of the part?
Unfortunately the only thing on the back of the device is under the epoxy on the back, but from closer examination, it's exactly what is on the side. Some stuff came up today that prevented me from moving forward on the investigation, but I will post again as soon as I find out more!
Well, good and bad news.... Lol. I had managed to get individual segments and digits to light up, and I had the pins mapped out however, I delved into the world of NPN transistors to control the digit selections off of my arduino pins and fried it. I didn't put a resistor on the base of the transistor and one way or another I killed the poor thing. So oh well, at least I successfully figured out the display.