I'm going to do another combo post here, simply because the design portion is quite straight forward.
And if I'm honest, this was probably the most stressful module to build in the entire clock, namely because the month name decoder is such a monster - if there was something wrong with the design, or some issue with my translation from logicly to EAGLE which then made its way in to the physical build, then it was going to likely be quite painful to fix.
The design work for this board is mostly covered in prior posts about 7 and 16 segment decoders, namely these ones:
Most of the additional design work was to take the logicly circuits and re-build them as EAGLE schematics, since all of my builds have been guided by such schematics (logicly was just for simulation and verification).
And if I'm honest, this was probably the most stressful module to build in the entire clock, namely because the month name decoder is such a monster - if there was something wrong with the design, or some issue with my translation from logicly to EAGLE which then made its way in to the physical build, then it was going to likely be quite painful to fix.
The design work for this board is mostly covered in prior posts about 7 and 16 segment decoders, namely these ones:
Most of the additional design work was to take the logicly circuits and re-build them as EAGLE schematics, since all of my builds have been guided by such schematics (logicly was just for simulation and verification).
As you'll see when you look at the schematics linked below, theres quite a lot going on in the month name decoder. It has a lot of gates which are connected together and was going to make for a challenging build.
The day of week decoder is quite tame in comparison, and the decoders for day of month have been built before on the time decoder module and so are tried and tested, and actually were very simple to put together.
So, the build. As I was expecting a fairly dense board for this build I decided to give myself as much room as possible and started laying out my transistors right up against the bus connectors at the bottom of the board. This made things a little interesting when connecting the various output gates to the bus, but overall it wasn't too difficult.
The first decoder to be built was the day of week, which would display something like MO, TU, WE etc. This build, as anticipated, went very smooth, and there were no issues encountered - it just worked. Phew - one down, two to go.
With the partially built decoder board in the clock I cycled through each of the 7 days of the week using the day of week set button on the calendar module and was pleasantly surprised to see all of the short names reading out as I had designed them. Here's a small selection:
With the partially built decoder board in the clock I cycled through each of the 7 days of the week using the day of week set button on the calendar module and was pleasantly surprised to see all of the short names reading out as I had designed them. Here's a small selection:
Next were the day of month decoders. I'd already built these kinds of decoders before, and I didn't expect to hit any snags with these either, and nor did I. Two down, one to go, and so far everything was running fine giving me this:
Once again I cycled through all possibilities to ensure the correct numbers and sequence were displayed, and I also cycled through the various months to ensure that the counters would reset and count the correct number of days per month, this also proved to work perfectly.
I was feeling slightly more confident now that I was about to head in to what I felt would be the most difficult part of the build, the month name decoder. I figured the best way to go about it was just start doing it, and deal with the issues as they came up. To help, I would build the decoder "letter by letter", and use the logic analyser of my scope to check the outputs (8 at a time) were in the correct states for each month of the year. Heres a glimpse of how I went through that process:
Power and inputs to the decoder board in this case were supplied by a battery and some wires off a breadboard. I thought it would be easier if I had to make corrections, and didn't have to keep building up and tearing down the stack of boards.
Through this process I did happen to come across some mixed up connections which had occurred during my translation from locigly to an EAGLE schematic. It was a matter of buzzing out the suspect signal wires with my multimeter, working out what had gone wrong, correcting the schematic and then re-soldering wires to the correct topology.
I kept at it and eventually I got to the point where I soldered (what should have been) the final 10 transistors!
And after wiring it all together and testing the outputs with my logic analyser I was at a point where I wanted to plug it in and test it with the display board instead of looking at high and low signals on a scope!
And, after plugging it in I was greeted with a most welcome sight (after first closing my eyes and psyching myself up to open them, hoping to see the right output)!
Or so I thought, until I moved the month along to February.....
Hmm, that's not right! This turned out to be a very simple fix, however. After verifying that the calendar module was indeed outputting the correct signals to the correct pins, I tracked down and corrected two crossed wires on the display board. That fixed it right up, and cycling through all of the months I got a perfect readout for all of the names - just as designed in a spreadsheet all those months ago!
AMAZING I'm thinking - it's pretty well DONE.
It was at this point that I showed the clock to a friend, and after attempting to demonstrate the month rollover where the day should reset to 01 instead of 00 that I discovered the issue where it actually rolled over to 00. That was then corrected (or so I thought) with a little additional circuitry.
But I have since discovered another issue. On July 29 when the date should have incremented to July 30 it actually rolled over to August 00. Ahhhhh crap. So I'm currently pondering the solution to this, and I think I know why it is happening, and what the fix will be. Stay tuned for a later update about that (I really hope this isn't going to become a recurring theme.......) 😔
Anyway, it's actually very useable as a clock and calendar at this point, despite some niggling issues which I will hopefully resolve in time.
Here is the end result for this board:
As always, schematics are linked here:
And with that, it's basically done now. I plan to write a "debrief" post and talk about things that went well, what didn't, and my general thoughts of the project. Stay tuned for that in the near future.
As for the fix for the rollover issue, I will get to it in time. After such a massive project I want to take some time to do a lot of stuff that I didn't do while I was doing this, and basically do anything but this for a while! The display dimming board will also come at some stage in the future as a result.
Anyway, it's actually very useable as a clock and calendar at this point, despite some niggling issues which I will hopefully resolve in time.
Here is the end result for this board:
- GitHub repo
- calendar-decoders.sch EAGLE schematic file
- calendar-decoders.pdf
And with that, it's basically done now. I plan to write a "debrief" post and talk about things that went well, what didn't, and my general thoughts of the project. Stay tuned for that in the near future.
As for the fix for the rollover issue, I will get to it in time. After such a massive project I want to take some time to do a lot of stuff that I didn't do while I was doing this, and basically do anything but this for a while! The display dimming board will also come at some stage in the future as a result.
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