Digit Display Problem

[ducksauz]

After letting it sit on the bench for a couple of months, I finally got around to building my Defusable Clock kit this weekend. I seem to be having a very odd issue with digit display. At first I thought it was a debounce problem, as I was trying to set the time and the displayed hour would go 1,2,3,0,1,2,3,8,9,10,11,12. Then I noticed that it was consistant, so I started hacking around.

First thing I did was hack the code to make it a 24 hour clock instead of 12 hour. This wasn’t to debug this issue, but just for my preference. Next, I moved the minute button to pin 2 and hour button to pin 3 and proceded to comment out any tests for alarm or detonate presses so I could use the serial port to print some debugging info, i.e. the time that it thought it was set to.

Now that I can compare display vs. internal representation, and I can see that the issue is consistant across all 4 digit positions.

Internal - Display

0         0

1         1

2         2

3         3

4         0

5         1

6         2

7         3

8         8

9         9

OK. That’s pretty obvious. Bit 2 is always zero. I check for shorts and QB on the ‘595 and IC on the ‘247 are shorted to ground. I don’t have any solder bridges. I can take some high resolution pictures if you like, but is it possible that this might have slipped by the board house electrical testing?

Also, does QB make sense for bit 2? I would have thought it would be QC, but it looking at the schematic, it looks like things are flopped around (QA->ID, QB->IC, QC->IB, QD->IA), so perhaps that makes sense.

[Michael]

Thanks for investigating the problem in depth, and sorry you’re having problems. The boards are electrically tested, but the board house claims there can still be a fault rate of up to 2%, so we have encountered a few bad boards out of hundreds sold. You may have been unlucky.

Have you tried reflowing the QB on the ‘595 and IC on the ‘247 pins? Maybe the solder mask is exposing part of the ground plane (bottom of board is ground plane) and there’s a tiny short. I’ve experienced some shorts like this and have fixed them by removing a bit of solder. If you can’t get it to work, I’ll replace the kit, of course. Just keep me posted.

The pin assignments seem funny because on the ‘595 in A is the most significant bit, but on the ‘247, pin D is the most significant bit. So the connections are (ABCD) -> (DCBA).

[ducksauz]

So, a month later and I finally have a quiet Sunday afternoon to spend in the shop. I just solder wicked the QB and IC pads and I’m still getting the same issue. 🙁

Any other suggestions?

[Michael]

Sorry it wasn’t resolved. I will send you a new kit. Please email support@nootropicdesign.com with your details. If you ordered from us directly, just remind me what your order number is, or name or whatever. Again, sorry about the difficulties.

[ducksauz]

Email sent. Thanks for replacing the kit.
That’s some serious customer service. 😀

[Author]

Posts