Dual led alphanumeric display

[HarveyH42]

I've got a couple dozen of these displays, but can't find a datasheet or pinout. I did find a basic specs sheet, but was too useful. Mostly I got that they are red, and common cathode.

On the part:

IEE 3785R
8504 3

Also goes by LR3785R. There are only 13 pins, but each digit has 14 segments (counting the decimal point). So, I have no idea how they work the magic, 28 LEDs with only 13 pins... Haven't tried applying power yet, they are nice clean pulls, hate to destroy one, but wouldn't hurt anything.

Anyway, I was thinking of building a clock, that spells out the time, instead of using numbers. Something different and unique.

 

[Pommie]

Could they be wired as 4 seven segment displays so that normal drivers can be used?

Mike.

 

[justDIY]

IEE was a company purchased by Fairchild some years ago, but recently Fairchild dumped their opto division and promptly removed all data sheets from their website

My guess is the array is internally charlieplexed somehow?

 

[HarveyH42]

Did a lot of searching, with no luck. Even tried Ebay ($3.50 each), but not hookup info. Should have asked, but didn't want to register. Guess I'll have to do the power/probe method and see which pins light up what. Maybe I can find a cross reference or similar part. Think I'll search a little more first.

 

[on1aag]

Hi HarveyH42,

There was a description at Epay:

6 common cathode pins and 5 segment (anode) pins.

I learnt at school that 5 X 6 = 30.

Switch your multimeter to diode test and hook one test lead to one
of the pins and start touching the other pins one by one with the
other test lead. If you can't measure anything don't panic, reverse
the two test leads.
If this doesn't work select another pin of the display and do the same.
If this doen't work either select a third pin. (It is possible that you
selected the two combinations that are not connected. 30 possible
connections and only 28 segments.)

on1aag.

 

[Pommie]

Could they be wired as 4 seven segment displays so that normal drivers can be used?

Not a chance.

Why is 5*6 any more logical than 4*7?

Mike.

 

[on1aag]

Hi Mike,

Why is 5*6 any more logical than 4*7?

It isn't, it could be either way. But there was a description of that
display at Epay . . .

on1aag.

 

[HarveyH42]

Information from Ebay isn't the most reliable. It's kind of a shot in the dark, better then nothing. Will give the diode test a shot after work today. I uploaded a couple of photos, maybe somebody has seen similar pin configurations on a different display that I can get a datasheet for.

I laid them out (got 20) to see how long the clock would be, about 12 inches. Didn't get around to counting characters to see if 40 would be enough to do what I want without scrolling. Might be close.

 

[HarveyH42]

Okay, finally sat down and figured out the pins. There are 4 commons, and each display is divided in half, diagonally. Uploaded a diagram I did, kind of sloppy, but shows what I needed to know. Have know idea yet how I'm going to program this mess, 11 pins for every two characters... Maybe there is some driver chip for this, but probably going to be as elusive as the data sheet...

 

[k7elp60]

I bought some Kingbright dual digit alphanumeric displays myself and luckily I have the data sheet and they are wired in a similar manner as yours. What I see on yours is this. Segments for both digits share a common pin, but to select that digit the ground is the key, in your case segment A for both digits is the same pin, but the grounds are different. I would try a resistor on the segment pin and then multiplex the grounds. As far as a driver I haven't a clue either. Seeing your connection diagram has helped me remember what I bought mine for and perhaps I'll figure out a driver soon.

 

[blueroomelectronics]

Treat them like a 4 digit common cathode display. Very neat actually.
What was the Kingbright part number.

 

[k7elp60]

Treat them like a 4 digit common cathode display. Very neat actually.
What was the Kingbright part number.

PDA54-12GWA

 

[blueroomelectronics]

Thanks, I would build a kit around them but not sure how well it would sell.

 

[aries1470]

Hi,
I think this will be my 1st post, after lurking in the forums for a little while.

I was able to find this info only on this display.
-------------------------------
LR3785R

Industrial Electronic Engineers :: Segmented Alphanumeric LED Display - (8.8.)
Specsheet / Datasheet


Package Style (Basic)=2-Edge

Number of Characters=2

Connection Type=Comm Cath.

Color=Red

Character Height (mm)=14

Peak Wavelength (m)=655n

Iv Min.(cd) Luminous Intensity=250u

@I(F) (A) (Test Condition)=20m

V(F) Max.(V) Forward Voltage=2.0

@I(F) (A) (Test Condition)=20m

I(F) Max. (A) Forward Current=25m

Package=2-Edge
-------------------------------

I should soon have a couple of these. If the case is as HarveyH42 has uploaded, it would make my life even more difficult. ( I was looking at a different dual alphanumeric when I came across these.). I think I will have to do some more serious thinking, since I am only a beginner, and that would mean I must think on how to do a multiplex.

I am in the development stage of a clock, PLUS a DAY of the WEEK ;-) so if if I have to multiplex, I am thinking of using a 555 timer somehow... to be switching the electrical on and off.

Anyhow, I will post once again in this thread, for part of the circuitry that I am doing once I receive the led's and will need help

 

[aliexdsg]

thanks Harvey,,,your post is very useful for me thanks