Help with 16-Segment Displays on Pro Dev Board

Entomy

I think I must be mentally deficient in this area or something. I've gotten nearly everything else working fine, and understand why it works. But I'm completely confused by the 16-Segment displays. I don't seem to understand how to wire them. I checked the manual for this board, but I guess I don't understand what the letters for the pins mean, or something. Any help or explanations? Thanks in advance!

Duane Degn

If you connect one of the "DIGITS" connections to ground you "turn on" that particular digit. By applying a positive voltage to one of the "SEGMENT" connectors, you'll turn on that particular segment. For example if you connect 3.3V to "C" and ground to "R. DGT3" the bottom right vertical segment of the last digit lights up.

By setting the segments you want lit high you can have these segments show up on the digit you want by only setting the desired digit pin low. The digits you don't want lit will have their cathodes held high.

My cycling through each digit one at a time, quickly, you can make the display show any combination of segments you wish. The Propeller can easily cycle through the digits fast enough that they shouldn't appear to be turning on and off.

I'm pretty sure there are enough I/O pins on the Propeller for the Propeller to drive the display directly. However if you want to use some pins for other purposes, you'll want to use a some sort of shift registers to control the display.

The 74xx595 shift registers work great for driving the display. TonyP made a small PCB with '595 chips which works great for this purpose.

TC

This might help

Each letter on the "SEGMENTS" connector corresponds to its segment.

tonyp12

I still have the add-on boards for sale:
http://forums.parallax.com/showthread.php/134106-Updated-17seg-LED-driver-for-PPDB-now-available.

Entomy

Thanks both of you; the two were exactly what I needed.
It seems like every segment except A2 works; why would this be? Connecting it to any pin does not work, even if that pin drives other segments just fine. The A2 on every segment does not work, which is extremely strange to me.

Duane Degn

It sounds like you have a bad solder joint somewhere. You could try touching both sides of the A2 resistor with a hot soldering iron. You might want to check to see where the circuit is broken by testing on both sides of the resistor with a multimeter. You could also test to make sure there's a connection from the header to the close side of the resistor.

Entomy

Don't have a multimeter on me right now, as someone borrowed mine for a circuit way more intensive than it could handle (grr...). The solder joints looked fine to me under 40x mag. But diagnostics through jumping revealed some strange behavior. It's causing me to think the resistor is flawed, until I jump through a viable resistor to postresistor A2, which causes the supplying segment to completely shut off, and A2 still doesn't light. I'm now confused rather than unknowledged, which an improvement for sure, but not a point I wish to stay.

Any ideas, because I'm fresh out?

Duane Degn

I don't think I understand what you mean by this.

Entomy wrote: »

which causes the supplying segment to completely shut off, and A2 still doesn't light.

What is the "supplying segment"?

If connecting to A2 is causing other segments to turn off, it may be you have a short on one of the A2 solder joints. The A2 pin is the top right (looking from the top of the board) pin of each display module. Take a look at the back of the board and make sure the solder on this pin isn't touching the ground pour on the bottom of the board. Most of the copper on the bottom of the board is connected to ground. If a solder joint is too large, it can end up shorting to ground.

How to the solder joints of the A2 pins look?

Edit: You may need to move the black rubber foot to inspect the A2 pin of the far right display module.

Edit again: Where did you get this board? If you purchased it from Parallax recently you may be able to exchange it. Though I think it's a shame to exchange it if it can be easily fixed.

Entomy

The "supplying segment": For segment A1 supplying segment A2, a jumper is placed such that power additionally flows to A2, as well as the original A1.

I believe I may have found the problem, but need to pick up a new meter to be sure. It looks like at some point, a small part of bluish coating came off, exposing the copper, which the solder seems to be touching. Even without the meter, I'm near certain this is the problem, as it explains what I've been seeing perfectly. I ordered the board through Amazon, but the seller was Parallax. If I'm right though, I can easily fix this problem.

Duane Degn

I agree with your diagnosis.

I think the way boards are soldered in a factory requires the solder mask to be intact. I think any exposed metal gets soldered. I think they call it "wave soldering" since the boards pass over a standing wave of molten solder.

Solder wick makes removing excess solder really easy. You can probably fix the problem without solder wick but if you'd like to try it, send me a PM with your address and I'll mail a foot of it for you to try.

Solder wick is great stuff to have on hand. It's really useful when soldering surface mount parts. Just glob the solder on to the leads and suck the extra off with solder wick. You'll wonder how you ever got along without out it (assuming you don't already use it).

Parallax is really good about replacing defective parts but I always hate to send a board back if it's easy to fix it myself.

I hope you let us know how this turns out.

Entomy

I appreciate your help, and assuming I remember, I will report my success or failure back here.
I do know about solder wick, and have plenty myself. :P Thanks for your kindness though; I'm sure it's been much appreciated by others. I'm very comfortable doing programming, and pure electrical circuits, but have never mixed the two for embedded/uC applications. I spent a lot of time trying to find a suitable platform. The big thing I didn't want a desktop style processor, just scaled down, which many seem to behave like. I've been very satisfied with the Propeller, Spin, and this board. The community seems great so far too.

Entomy

Got a new multimeter yesterday, and it confirmed our suspicions. I desoldered the guilty joint, deposited some plastic I assumed to be a safe insulator, resoldered, and... it works!
Thanks to those who've helped, it's been much appreciated.

Publison

Entomy wrote: »

Got a new multimeter yesterday, and it confirmed our suspicions. I desoldered the guilty joint, deposited some plastic I assumed to be a safe insulator, resoldered, and... it works!
Thanks to those who've helped, it's been much appreciated.

That's good news!

That's unusual because Parallax has a great history of quality workmanship.

Please visit here often.

Jim

Entomy

I think it was damaged post-work, maybe during transit or something. The way the coating looks, is almost exactly like something chipped it. After that, the soft metals in solder could easily droop a little, coming into contact with the copper base. At least, that's my guess as to how it happened.

Even while inspecting the board under x40 magnification, the workmanship was impressive. I had originally expected poorer quality, as the price of this board is nowhere near many professional dev boards for things like the PIC, MIPS, et al. Oh how foolish that seems now. I'm very impressed by this thing, in price, quality, design, and utility. With the crappy quality of many goods nowdays, I expect to have to fix several things; fixing only one simple issue is a nice change. I definitely feel like I made the right choice in microcontrollers to learn and work with.

Chris Savage

Glad you got it corrected. The PPDB is my main and favorite development board.