I admit it: I'm a total geek. I love electronics, programming, 3D art, vintage Apple hardware, and whisky. I'm always juggling half a dozen projects. I also enjoy documenting it all: my successes, my failures, my experiences... and everything geeky along the way.

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Upgrading My Old 7490 Clock, Part III | Kevin Rye.net - Main

Kevin Rye

Geek Extraordinaire. Yeh, I said it.

Upgrading My Old 7490 Clock, Part III

Since I wasn’t happy with the engraving on the first spin, as well as totally forgetting to make a cut out for the display, I revised my SVG file and resubmitted it to Ponoko. They must have been on a roll this time because my order shipped the next day and was in my hands 3 days after that.

7490take2acrylic_0035

Looks good, but where’s my engraving?

7490take2acrylic_0037

Phew! That was a close one. It was on the other side under the tape that holds it all together.

Ah! That looks much better!

7490take2acrylic_0040

However, the engraving for my name and date didn’t come out too great. Dang! I thought I used the same font style and size as before and it looks like half of it didn’t even go through the paper. I didn’t want the name and date raster engraved, just lightly etched like the Hours and Minutes labels were before. I don’t know if that’s my mistake, or theirs. I just hope it doesn’t look too terrible when I take the tape off. I really don’t want to have to buy a 3rd panel.

7490take2acrylic_0042

For the front panel insert, I had one cut out of translucent red.

7490take2acrylic_0036

It fits like a glove!

7490take2acrylic_0044

Speaking of things fitting like a glove, so does the display. I couldn’t have gotten that any closer if I tried. It’s perfect!

7490take2acrylic_0046

As far as the color, I think it’s going to look pretty good. I might lower the value of the resistors in order to brighten up the digits. I’ll have to see what it looks like when it’s all put together.

7490makeovercaseassembly_0064

Paint time! I masked off everything but the text.

7490take2acrylic_0045 45

I then took it outside and gave it a light coat of flat paint.

7490take2acrylic_0050

After it dried, I crossed my fingers and peeled off the tape. Man, that looks good!

7490take2acrylic_0053

As far as my name/date, not so much. I just hope when the whole thing is put together, it’ll hide itself under the power cord and you won’t even see it. I thought about just buffing it out, but I’ll probably just make a mess of it.

To hold to top cover on, and make it easy to remove, I want to keep it on with magnets. I don’t want to start drilling holes and adding screws. I hit up the craft store and grabbed a few packages of magnets.

7490clockmagnets_0001

I then flipped the case over, removed the bottom, and peeled back enough of the protective film to expose the area where the magnets will be glued.

7490makeovercaseassembly_0003

I then glued one magnet to the front panel, and one to the top case. I used some super heavy duty epoxy.

7490makeovercaseassembly_0005

When the glue was set, I took it apart again. I inserted the red panel and secured it with a length of clear tape.

7490makeovercaseassembly_0051

I then glued everything together with some hot glue.

7490makeovercaseassembly_0060

A few days later, my PCBs arrived in the mail.

7490reworkPCBsarrived_0067

I got to work on soldering it together. It was a pretty easy build.

7490reworkPCBassembly_0072

I plugged in an LED and watched it blink away. It’s alive!

7490clockrebuildfinal assembly_0003

I then mounted it onto the clock main board with a few board stands.

7490clockrebuildfinal assembly_0006

I then started putting together the various custom cables that I’d need for all the connections.

7490clockrebuildfinal assembly_0007
7490clockrebuildfinal assembly_0010
7490clockrebuildfinal assembly_0009

I also reconnected the reset switch which sets all the segments to “9”. I won’t need it when all is said and done, but it’s a quick and easy way to make sure I didn’t knock a wire off one of the displays during assembly.

7490clockrebuildfinal assembly_0017

Previously, I was knocking the 60Hz line signal down to 1Hz and passing it through a bridge. So I ended up with a nice 5V square wave. This time around, I’m using a digital pin on a microcontroller. It’s either HIGH or LOW. There’s no “OFF”, so I needed to wire-in another diode to stop the signal from conducting on the output pin of the previous stage when setting the clock.

7490clockrebuildfinal assembly_0020

In theory, this should have all worked, but the signals are still getting crossed. Once the seconds reach 40, the minutes section starts counting on its own.

I need to do a little more tweaking. If I can’t fix it with a few more diodes, I might have to redesign the I/O board. I might just use one of my Barebones Arduino boards. That way I’ll have way more digital pins to play with. I can tie all the outputs and inputs of each 7490 stage to a separate digital pin. I probably should have done that from the beginning. After all, this is the exact type of project I designed the Barebones Arduino for.

See this project from start to finish:
Digital Clock 1.0
Upgrading My Old 7490 Clock, Part I
Upgrading My Old 7490 Clock, Part II
Upgrading My Old 7490 Clock, Part III
Upgrading My Old 7490 Clock, Part IV
Upgrading My Old 7490 Clock, Part V