My nixie clock project - Page 1
Forum section: electronics / projects

author: Ketturi
author_rank: Regular Contributor
timestamp: November 22, 2012, 05:04:23 pm
content: Hello World!Nearly year ago I started to think building my own nixie tube based clock. Last winter I ordered tubes and started to build the clock.My intent is not to be rude and advertise my blog but I think it's much easier to just post links here.http://ketturi.kapsi.fi/nixie-clock/This is first page, where I generally describe project.http://ketturi.kapsi.fi/2012/10/mainboard-for-nixie-clock-and-burned-fingers/In here is post about clocks control boards. I made circuitry to single doted vero board because I don't have equipment to make PCBs and getting them manufactured is out of budget(and new style smd pcbs really don't fit in devices imitating old prototypes). Soldering and layout are not the best, but both boards worked with first try.http://ketturi.kapsi.fi/2012/11/updated-nixie-clock-schematic/This is final schematic which is bit unclear and cluttered. I need more practice with drawing circuits, because always they explode on paper.http://ketturi.kapsi.fi/More posts regarding the nixie clock can be found from my blog, which also includes more electronics and stuff.At this moment I am stuck in coding, which is my Achilles heel, my experience is from QuickBASIC and way I'm thinking is not suitable for emended microcontrollers.So I tough this could interest you my fellow hobbyists and engineers. What are your toughs about this project, should I add something or fix/modify something.And does anybody have good ideas for front panel, it's almost biggest problem I have.PS. My grammar sucks and my grammar nazi editor is taking a break

author: c4757p
author_rank: Super Contributor
timestamp: November 23, 2012, 03:08:03 am
content: Looks good. A few observations/questions:Why the low values of the transistors' base resistors? Surely you don't need 13mA into the MPSA42s and 9.3mA into the BC547! I'd have used 10k and 33k respectively, assuming a worst case hFEof 25 and 100 respectively.AVCC and AGND should be connected even if you don't need the ADC; you can have somewhat mysterious problems if they aren't. The ADC isn't the only thing that uses them.The PCF8574 is perhaps a bit advanced for just latching four BCD digits - it's expensive, more of a pain to use in software, and doesn't have the same promise of future availability (though it's notthatbad in that area) as something like a 74HC595. (Not that future availability is really an issue on something that's probably a one-off...)I know two-column headers are tricky on this kind of board, but they're doable. Maybe you could use a more standard ISP header?Your switches should probably have stronger pull-ups than the ones built into the ATmega. A SIP resistor network would be easy to stick in there, since all those pins are in line.Series resistors between the microcontroller and the pushbuttons will help protect the microcontroller from ESD picked up from fingers and the like. Put them between the microcontroller and the pullup resistors, or you'll just make a voltage divider.On the same note, if the signal for the high voltage power supply goes off board, I'd put a series resistor on that too. In fact, depending on how noisy that power supply is, I'd consider putting a bit better protection on that line to protect the MCU from noise it generates. High-speed clamping diodes, etc.Feature idea: you could feed the CR2032 battery voltage into one of the ADC or comparator inputs for an easy "low battery" indicator.Using net labels to make connections can make for a confusing schematic. You might as well just draw the wire between the two "TUBE_PSU_CONTROL" points.I like to see that you made sure there was a short path between the HV input's ground and the 74141s.

author: Ketturi
author_rank: Regular Contributor
timestamp: November 23, 2012, 01:24:19 pm
content: Quote from: c4757p on November 23, 2012, 03:08:03 amHi, many of these decision were made because of available parts and knowledge I did not have year ago.This is clearly my mistake, I haven't calculated it but chosen first resistors I have found. I might change them.Actually these pins are connected, my mistake again in schematics, they are wired under the ic socket, and thus not showing in pictures. Without these whole A port is not workingIt seemed to easy way and I already have i2c line in use. They are not very hard to use, just I2c.write to address and data. For bigger production they are expensive, but I sourced them like lot of 5 at 3.50€ISP header is one line header, because my programing cable have one line header in addition to normal ISP connector, but yes, if I had made PCB I would have used normal 6 or 8 pin connectorMistake again, must actually add them because switches have some problemsESD should not be big problem with grounded metal buttons. Sorry but I don't fully understand how you mean resistors to be connectedIt have pull-down on HV supply side, Im thinking to add some protection to hv supply side.That could be useful, thanks!Thanks for the feedback, it helps always to notice things and improve design. I'm blind for my own mistakes because assuming I'm always right.

author: c4757p
author_rank: Super Contributor
timestamp: November 23, 2012, 01:59:38 pm
content: (Wish I knew how to make a proper list with arbitrary numbers...)2. Really, the whole port A? Wow. It's been a while since I've done AVR.3. The PCF8574 thing was a bit of a nitpick, I agree, they're fine. I'd have chosen the 'HC595 over them, but I'll admit to maybe just a bit of 7400 fanboyism...6. Grounded metal switches? Do they actually have a ground pin, or is the metal just touching a metal chassis or something? Interesting. (And I'll attach a quick sketch of what I meant with the resistors)"I'm blind for my own mistakes because assuming I'm always right." Yeah, I know what that's like...