Been really trying to move along with this project, keep that wave of enthusiasm going and all that. I’m happy so say I have the first board complete!
Random notes on board one
It is immensely pleasing to have that finished finally. I did power it up and test everything, got the logic probe out and it is, indeed, counting out seconds for me. Hooked up all the switches and board interconnects and made sure everything works properly. Mainly a day of soldering the last bits on, crimping connectors, heat shrinking bits here and there. Quite relaxing for a sunday.
It feels like I have a functional block working and that is set in stone. A milestone to be sure.
On to board two
I’m sure if anyone is reading this, you’re screaming at me as to why I wasted so much space, or why I’m using protoboard, or why I didn’t just get my own pcb etched or fabricated. You’d be correct, this is a rather inefficient way to make electronics projects. Truth is, I’m not all that advanced, as you can probably tell. I don’t have ferric chloride and acetone at hand, nor copper boards. I certainly also do not want to wait weeks to get a board made in China. It’s also apparent that I’ve modified this project many times during its construction and it would have caused me to re-spin or bodge the board several times before coming to the current iteration. I’m still learning okay?
Board two: the squeeze
I did a test fit of the major components on board two, and I realized why I had originally envisioned having the minutes 4017s on board one. It’s going to be a really tight fit!
That’s 30 MPSA42 transistors there and I’m still mucking about with the layout. It’s apparent I’ll make two rails ground just to slot jumpers from the emitters of each transistor. The 33kΩ resistors on the base will have to be part of the wire going to it as there’s no place on the board for a separate trace for them. Flappin’ in the breeze, as it were. No worry, I’ll heat-shrink the connections so there’s no sparkies and zip tie the bunches.
Speaking of those 33kΩ resistors – I’m going to need a bunch of them! About 40 to be safe. Another trip downtown as I can’t be arsed to order online. There’s always something!
With those in hand, it’s merely a case of soldering it all up nicely. I’ve had a lot of refresher in the last week and I’m confident it will go quickly. I will of course have to do go/no go tests on all the components before whacking them in. I’m hoping I have no dead transistors as I literally have one extra. Not enough margin knowing me. At least I’m confident the EBC configuration of these transistors matches the datasheet as I was playing with it just the other day.
Beyond board two
Lastly, will come the big problems of mounting the tubes and fitting it into a nice case. I want to keep the tubes on their own board with a universal cable. I’ve heard something about tubes degrading and sputtering if left constantly on one digit. This could be a problem for the hours digits that may experience some uneven wear. If I can open it, and change which role each tubes have, then I can swap them around every so often to even out the wear across all tubes.
Another solution I had thought of is simply a switch to turn the tubes off entirely. This will let the circuit keep time while the tubes are not being worn out while I am not paying any attention to it. I was going to fit this switch’s connector on board two, but we may have to see if that is still viable, again space is very tight on that board. I think I should be able to fit it in.
This is been a puzzle i’ve been knocking about in my head for a bit now. The tubes are rather delicate, I have no replacements and are unlikely to find any, so I had better be very careful. I’m thinking of mounting them on a bit of perfboard (without copper), running the leads in a pattern that is closest to their natural circle and securing them somehow, maybe hot glue or epoxy … not sure what would be best. In the middle, I need a 5mm hole to mount the blue LED that will shine from underneath. Probably hot snot the whole thing together and gently solder wires to all the leads and heatshrink each. Then crimp them into their 13-pin connectors (11 for the nixie and 2 for the LED) and they’ll plug right in to board two. That’s … 52 wires, how exhausting! Anyway, these single boards will screw into the top underside of whatever case I get for them. This part I’m most nervous about actually.