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Issue with 7 Segment Display with Backpack
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Issue with 7 Segment Display with Backpack

by Woozle on Tue Oct 08, 2019 8:22 pm

Hey all, hopefully someone can help me out here - I have an Arduino UNO, and am attempting to get one of the 4 digit 7 segment displays with the HT16K33 Backpack to work, however when I follow their instructions to run sevenseg, I only get a partial number to show in location 1, no response from the other sections, here is a picture of that:

https://imgur.com/gFAz7M4

It runs through the test with various flashing and stuff, it appears that only parts of the 2nd location show up (bottom left, bottom center, top left dont appear to work).

I have ran the i2c scanner that I found in someone elses post, and it showed the following:

https://i.imgur.com/bvwEw4E.png

My solder joints seem okay to me? I am new to soldering, here are the solder joints, the focus isn't great, was the best I could get my pixel 1 to do, it has been bad lately.

https://imgur.com/aEx5VEv

https://imgur.com/3wtj7OP

Any help would be appreciated! Thanks!

Woozle
 
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Re: Issue with 7 Segment Display with Backpack

by dastels on Wed Oct 09, 2019 12:57 pm

I would start by going over those joints again. Have a look through https://learn.adafruit.com/usb-rechargeable-cordless-soldering-iron for tips and such.

Dave

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Re: Issue with 7 Segment Display with Backpack

by Woozle on Wed Oct 09, 2019 2:36 pm

Thanks for your input, I browsed through that a little on my phone, and will read closer this evening. I watched a few tutorials online about soldering as well before I began, is there something specifically that appears off with the solder connections, so I know what to try and correct?

Woozle
 
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Re: Issue with 7 Segment Display with Backpack

by dastels on Wed Oct 09, 2019 4:23 pm

They didn't seem to flow smoothly up the header pin. I think of a good joint like this as looking like the roof of a circus tent. If the pin doesn't get hot enough, then the solder might not adhere well enough, giving you a sketchy connection. You also want to leave the iron on the joint for a bit (a second or less usually) so that the solder will flow into the hole. The holes are "plated through" meaning that the inside surface of the hole is covered with metal (joining the two sides of the PCB and any internal layers). That will give you a solid connection.

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Re: Issue with 7 Segment Display with Backpack

by Woozle on Wed Oct 09, 2019 8:34 pm

Hey, so I tried running back through some of them again, I feel like it is... improved some? Here is an album with a bit better pictures including the undersides - I am having this thing happen where I feed solder onto the pin/plate (I try to touch to both) and then it just seems like it is flowing through to the other side making a ball, none of these balls are touching or anything, though I am encountering the same problem with the display, not sure if that is bad solder job or normal.

This album shows a pretty good picture of both sets of the 7 pins, as well as the 4 header pins.

https://imgur.com/a/uuZVgsT

Is the oily looking substance on the board just flux, correct? Could that be causing me an issue, or is the solder job still not looking very good? I don't have a great soldering station, I have a Weller WLC100 40 Watt Station, it only came with a flat-head soldering tip, which I would much prefer one more pointed, but I feel like I am getting it settled against the plate and the pin by using the corner. The solder I am using is Kester 24-6337-0027 Solder Roll, Core Size 66, 63/37 Alloy, 0.031" Diameter.

Woozle
 
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Re: Issue with 7 Segment Display with Backpack

by dastels on Wed Oct 09, 2019 11:35 pm

They look good. Yes, it's just the flux. It's not conductive so it won't have an electrical impact. It looks a mess, but that's about it. Commercial products typically wash it off.

Let's look in more detail. Are some segments never on? On every digit? Are some digits never on at all?

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Re: Issue with 7 Segment Display with Backpack

by Woozle on Wed Oct 09, 2019 11:40 pm

Digits 1, 3, and 4 have never lit up.

Digit 2 lights up, but only the top, top right, bottom right, and middle segments appear to work. This is just what I've seen show up as it runs through sevenseg example sketch.

Woozle
 
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Re: Issue with 7 Segment Display with Backpack

by dastels on Thu Oct 10, 2019 11:37 am

It really sounds like a case of bad connections on the 7-segment display. Can you manually light other segments, by connecting cathodes to ground and anodes to Vcc via a small (220-ish ohm resistor)?

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Re: Issue with 7 Segment Display with Backpack

by Woozle on Thu Oct 10, 2019 12:02 pm

dastels wrote:It really sounds like a case of bad connections on the 7-segment display. Can you manually light other segments, by connecting cathodes to ground and anodes to Vcc via a small (220-ish ohm resistor)?


I agree that is definitely the most sensible issue... I am new to the world of small electronics and still learning, could you please explain a little more clearly to me what you mean by your test?

Also, at the moment the only resistors I have are what came with my original Arduino Uno pack, which are:

5x 100 ohm resistors
5x 1K resistors
5x 10K resistors

I definitely don't mind trying to source more resistors for the test, but I don't really know where I would get them out where I live, since Radioshacks kind of died out, I will have to search for a solution if those wouldn't work for your idea

Woozle
 
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Re: Issue with 7 Segment Display with Backpack

by dastels on Thu Oct 10, 2019 1:33 pm

You can use 3 100ohm resistors in series (end to end) to make a 300 ohm one.

Have a look at https://cdn-shop.adafruit.com/datasheets/865datasheet.pdf Page 3, the bottom diagram.

Each segment/LED is one of the arrow thing. each digit has all it's cathodes connected (the bar side of the LED), and corresponding segments in each digit have their anodes (the triangle side) connected together. So connecting a cathode/digit to ground, and an anode/segment to Vcc via the resistor (to limit the current and avoid blowing up/out the LED) you can light a specific segment. Not the easiest to do with it on the backpack, but doable. That will let you figure out if the problem is the LEDs. You can figure out the pins from the diagrams on that page.

Does that make sense?

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Re: Issue with 7 Segment Display with Backpack

by Woozle on Thu Oct 10, 2019 2:17 pm

It helps me a ton - I really appreciate it, I am at work right now but can start tinkering on it later.

I believe I understand everything, but I do have a couple questions I guess.

To make sure I understand, if I wanted to try and light up specifically the top segment of Digit 1, I need to hook to "A," on that digit (which is on Pin 13 with the rest of the "A" segments) with Vcc (and 3 in-line 100 Ohm Resistors to avoid damaging the LED), and ground out pin 14?

I guess I have two questions, provided that is correct:

First, the diagram on the document you linked to shows the locations of pins 1, 6, 7, and 12, but which would pins 13 and 14 be? The picture at the top of page 3 seems to suggest there is 12 pins?

And second, what is the best way to connect everything, is just wrapping wire around the resistors and the pins is not a reliable enough connection?

Woozle
 
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Re: Issue with 7 Segment Display with Backpack

by dastels on Thu Oct 10, 2019 8:12 pm

You got it in terms of the gnd/vcc connection.

Yeah.... The top view shows 1-6, 7-12 as you say, but the side view shows 7 pins. I would assume 1-7,8-14 instead of 1-6,7-12.

You could solder a wire for the goround, and the touch the VCC/resister wire to each anode in turn. Actually, solder wires yo the 4 digit cathodes, and ground one at a time to test the corresponding digit. That's how I'd go about it.

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Re: Issue with 7 Segment Display with Backpack

by Woozle on Fri Oct 11, 2019 7:43 pm

Sorry for the delay, I wasn't able to tinker any last night...

So, to update, I have now been able to test all 4 digits and can force them to light up each individually.

One thing I did notice, is that it seems that my segments were not lighting up appropriately? For instance applying power to Pin 7 would light up segments E and F together, and not the dots in the middle as it should. A lot of the top row (pins 8-14) were lighting up either segments E and F together, or B, however the bottom row acted closer to correct.

I wonder what would be the cause of that? Also, does this point to exclusively bad connections via my solder, (which I'm more than willing to agree with! :P) or a larger problem?

Woozle
 
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Re: Issue with 7 Segment Display with Backpack

by dastels on Fri Oct 11, 2019 8:52 pm

Bad connections or shorts possibly. Have a close inspection of the soldering.

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Re: Issue with 7 Segment Display with Backpack

by Woozle on Fri Oct 11, 2019 9:10 pm

I will check and see if there is anything, I feel like I've looked at them endlessly now and haven't specifically noticed anything.

Is it possible to de-solder the component? It doesnt seem like thats a thing really

Woozle
 
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Please be positive and constructive with your questions and comments.