Slightly overengineered nixie clock - Page 1
Forum section: electronics / projects

author: marshallh
author_rank: Unknown
timestamp: August 24, 2015, 01:16:54 am
content: I wanted an alarm clock to use for the next 20 years.FPGA powered with 32bit CPU, 128kx16 SRAMHardware MPEG decoding13W audio amp802.11n Wifi, SDMains or 12v brick powered544x tube compatibleRegulated HVIsolation slots did not show in 3d so I exported to the flexible CAD tool "MSPaint"Buttons/switches are on a separate sub-board over 1wire.I will update as I build it

author: Richard Head
author_rank: Frequent Contributor
timestamp: August 24, 2015, 11:22:45 am
content: Probably best to move C26 (electrolytic cap) away from the heatsink to ensure a longer cap lifetime.

author: ajb
author_rank: Super Contributor
timestamp: August 24, 2015, 02:17:44 pm
content: No battery backup?

author: dr.diesel
author_rank: Super Contributor
timestamp: August 24, 2015, 02:20:39 pm
content: Is wifi for NTP sync or media only?

author: Melt-O-Tronic
author_rank: Frequent Contributor
timestamp: August 24, 2015, 02:31:14 pm
content: What's the local time base?Related sub-question; how good will holdover be when an NTP source is unavailable?Related sub-sub-question; how resilient will timekeeping be to power failures?Edited to add my appreciation for over-engineering, especially on personal projects.

author: alexanderbrevig
author_rank: Frequent Contributor
timestamp: August 24, 2015, 07:38:55 pm
content: This is totally awesome! Nice work man

author: deephaven
author_rank: Frequent Contributor
timestamp: August 24, 2015, 07:58:46 pm
content: That is INSANELove it

author: tautech
author_rank: Super Contributor
timestamp: August 24, 2015, 08:41:43 pm
content: Beautiful work so far, thanks for sharing.

author: rsjsouza
author_rank: Super Contributor
timestamp: August 24, 2015, 08:52:35 pm
content: marshallh, you should be usingone of theseas your main clock timebase...

author: marshallh
author_rank: Unknown
timestamp: August 24, 2015, 09:00:52 pm
content: Quote from: rsjsouza on August 24, 2015, 08:52:35 pmSomeone turned me onto these...http://www.microsemi.com/campaigns/atomic-clocks/I have a 32khz and 50mhz quartz oscillator for timebase. Battery backup is nonexistent though I supose you could wire a 12v SLA to the jack and it would be a crappy UPS. Wifi is for NTP though it could be for streaming.Added a photocell forming a RC circuit on a FPGA pin. Should let me sense ambient light and dim the tubes that way. Shunt the voltage then see how long it takes to reach Vhth with the pin tristated.

author: rsjsouza
author_rank: Super Contributor
timestamp: August 25, 2015, 12:29:51 am
content: Quote from: marshallh on August 24, 2015, 09:00:52 pmNice part; thanks for sharing.Quote from: marshallh on August 24, 2015, 09:00:52 pmOne detail I am genuinely curious: on a base-2 processor, how can you accurately obtain 1 second timebase out of 50ms by using a binary divider on your CPU?

author: JoeN
author_rank: Frequent Contributor
timestamp: August 25, 2015, 01:23:25 am
content: It needs an OCXO in there somewhere. O0

author: marshallh
author_rank: Unknown
timestamp: August 25, 2015, 01:28:19 am
content: Quote from: rsjsouza on August 25, 2015, 12:29:51 amhttp://www.microchip.com/forums/m410159.aspxIf you need to generate an arbitrary frequency you can do so with a fractional-N counter. You will get good long term stability as long as you don't truncate the numbers, at the cost of increased jitter. I've done that to generate I2S clocks off a 74.25mhz clock. An analyzer showed the clock was in spec and with acceptable jitter.For longer term things you want to stick to old fashioned quartz. There are now lots of MEMS devices that are very cheap (I use them for base clocks and digital stuff) but they have poor long-term drift. They are more resilient for rugged environments since they don't exhibit piezo effects. A MEMS oscillator is basically a fixed output buzzing structure with loads of compensation circuitry to correct for PVT.They're sold under various frequencies by burning internal PLL settings.These oscillators have only recently become practical and they are quickly getting better.Another good way to get accurate time... just read the line frequency of the AC input.

author: JoeN
author_rank: Frequent Contributor
timestamp: August 25, 2015, 02:03:41 am
content: Quote from: marshallh on August 25, 2015, 01:28:19 amDo they really keep it that stable? I mean, for all applications other than clocks trying to tell time off the mains it doesn't matter one bit if it is off 1%, no other applications would ever notice it being off even that much, but that would kill basing a clock on it. If they are keeping it accurate it must be on purpose. Which begs the question, what timebase is the power company using?

author: c4757p
author_rank: Super Contributor
timestamp: August 25, 2015, 02:28:12 am
content: Many old-style plug-in clocks use mains as a time reference, and they generally keep fairly good time, so while I don't know the details, it's clearly accurate enough for household-use timekeeping.

author: marshallh
author_rank: Unknown
timestamp: August 25, 2015, 02:32:34 am
content: Quote from: JoeN on August 25, 2015, 02:03:41 amThe short answer is although the frequency does vary, it averages out by design.https://en.wikipedia.org/wiki/Utility_frequency#Stabilityhttp://www.intersil.com/content/dam/Intersil/documents/an13/an1342.pdfhttp://boards.straightdope.com/sdmb/showthread.php?t=446800

author: JoeN
author_rank: Frequent Contributor
timestamp: August 25, 2015, 04:05:13 am
content: Quote from: marshallh on August 25, 2015, 02:32:34 amThat's more or less what I figured. It doesn't matter a bit if the jitter makes some ticks off, as long as there are 5,184,000 in a day, and the next day, and the next. They can let it drift for a bit and then drift it the other way until the count comes back. I get that.Still, to do even this this you need an accurate timebase. I wonder what it is. I guess they have some sort of a feed from the national atomic clock.Thanks for the links.

author: dr.diesel
author_rank: Super Contributor
timestamp: August 25, 2015, 10:21:18 am
content: Quote from: marshallh on August 25, 2015, 02:32:34 amThat is interesting, I'd heard that rumor before, but as the principal software engineer for two 550MW units I can say there was absolutely no logic to accomplish the above. Frequency was calculated by rotor RPM, no correction was made between 3597 and 3603 and is fairly cyclic between those limit. So it will average, think I'll set my old Heathkit power line clock with my GPSDO later today.This might also be surprising, but there is no "standard" software suit for generation units historically, although some are starting to adopt control system manufacture standards. Which also don't included this correction.(trying to ponder if a couple specific units with control logic to attempt correction could be enough to influence the entire grid a few PPM.....)I will inquire further.

author: deephaven
author_rank: Frequent Contributor
timestamp: August 29, 2015, 01:27:47 pm
content: What chips are you using to drive the Nixies? I'm guessing they're Microchip (nee Supertex) but which one?

author: marshallh
author_rank: Unknown
timestamp: August 29, 2015, 06:16:57 pm
content: I think it was supertex HV5122

author: deephaven
author_rank: Frequent Contributor
timestamp: August 29, 2015, 07:52:49 pm
content: Quote from: marshallh on August 29, 2015, 06:16:57 pmThanks. I'm thinking of doing a layout using those but at the other end of the technology scale, just using a small PIC. Pain they need 12V logic levels!

author: Melt-O-Tronic
author_rank: Frequent Contributor
timestamp: August 31, 2015, 09:32:48 pm
content: Oh boy! I can't wait to see it populated.

author: Circlotron
author_rank: Super Contributor
timestamp: September 01, 2015, 02:52:43 am
content: Quote from: c4757p on August 25, 2015, 02:28:12 amThe mains frequency does vary a little from moment to moment, but over a 24 hours period they manage to have a more or less exact number of cycles. An interesting thing to do is to trigger your scope on the mains while watching a 5MHz or 6MHz signal. Someone starts pulling big power somewhere and as the mains frequency drops ever so slightly the trace slides to the left(?) then finally slows and stops when the steam has been automatically turned up and then it slides to the right(?) to get back to where it was. Entertainment for nerds.

author: MyElectronsFellOut
author_rank: Regular Contributor
timestamp: September 01, 2015, 06:53:23 am
content: The boards are looking very nice indeed.

author: xuio
author_rank: Contributor
timestamp: September 01, 2015, 09:48:25 am
content: Nice work!Definitly "a bit" overengineeredQuote from: marshallh on August 24, 2015, 01:16:54 amSeems like you are using Altium, you can set the slot layer (for 3d mode) by setting the route tool path:Design -> Board Options -> Route Tool Path -> Mechanical layer of your choiceMoritz

author: niekvs
author_rank: Contributor
timestamp: September 01, 2015, 12:26:29 pm
content: Quote from: deephaven on August 29, 2015, 07:52:49 pmYou can use the SN75468. It's cheap and more easily available, and no messing around with 12V. You do need an extra diode.Also seehttp://lucsmall.com/2011/07/19/using-the-sn75468-as-a-nixie-tube-driver/Less than 50 cents each, including shipping:http://www.aliexpress.com/item/SN75468-SOP-16/32339132658.html?spm=2114.031010208.3.1.PX1i29&ws_ab_test=201407_4,201444_6,201409_5

author: LaserSteve
author_rank: Super Contributor
timestamp: September 01, 2015, 06:51:46 pm
content: The US Government is in the process of allowing an experiment in the Midwest to see how ignoring frequency shifting on the Grid System would help with increasing network efficiency. That may or may not spell the end of accurate 60 Hz.http://spectrum.ieee.org/tech-talk/energy/the-smarter-grid/power-system-experiment-in-us-means-clocks-will-speed-upSteve

author: dr.diesel
author_rank: Super Contributor
timestamp: September 01, 2015, 07:29:58 pm
content: That article is from 2011, no link to what they found during the experiment.

author: dr.diesel
author_rank: Super Contributor
timestamp: September 04, 2015, 02:58:02 pm
content: Quote from: dr.diesel on August 25, 2015, 10:21:18 amSo I set my power line clock in sync with my GPSDO just after I wrote the above, isn't now 11 seconds slow. Hardly evidence whatsoever, clock could be missing pulses etc, but.....Also talked with the Controls group, no ones ever seen/heard of any control logic to support time adjustment or sync.

author: kwass
author_rank: Frequent Contributor
timestamp: September 04, 2015, 04:18:56 pm
content: Quote from: LaserSteve on September 01, 2015, 06:51:46 pmHere's an interesting website that shows the current AC mains frequency within each subgrid in the US.http://fnetpublic.utk.edu/gradientmap.html.The have a world-wide map too, but it's hardly the whole world:http://powerit.utk.edu/worldmap/I think that ending the accurate 60Hz mains frequency would be a terrible idea. There are many millions of clocks in use that would be obsoleted. Some test equipment measurements would not be as accurate either. For example, averaging readings over many power line cycles could potentially constitute different rather time periods, depending on how much the mains frequency is allowed to vary.

author: knks
author_rank: Regular Contributor
timestamp: September 14, 2015, 10:37:27 pm
content: Quote from: marshallh on August 25, 2015, 02:32:34 amVery interesting... Anyone knows is it the same in Australia?

author: free_electron
author_rank: Super Contributor
timestamp: September 15, 2015, 01:05:17 am
content: You forgot the obligatory blue (or other color) led's in the base of the tubes so you can make them glow ...

author: marshallh
author_rank: Unknown
timestamp: September 15, 2015, 01:13:07 am
content: Thought about it but decided not to, I just never was a big fan, and you can't get a nice complementary color with LEDs, neon produces wider spectra output.I started making a smaller russian tube clock also with IN-16s which i will put some possible red/yellow bicolor LEDs in.If anyone needs some very small neon bulbs (these are grain of rice sized) for colon seprarators just PM me. I bought 500

author: marshallh
author_rank: Unknown
timestamp: September 18, 2015, 01:51:30 am
content: LV (<12vdc) parts work great, blinking LED! Now onwards for high voltage blinking things!

author: marshallh
author_rank: Unknown
timestamp: September 18, 2015, 08:02:32 am
content: Running now, but with a very high pitched whine (like a TV flyback). Tried with another transformer that works, same thing. This is a duplicate of a PSU I assembled a couple years ago. Not sure why this time it's noisy. Poking and squeezing the transformer doesn't change anything. It gets worse with the duty cycle (currently around 5% loaded).My last idea is to check all ceramic capacitor skus against the ones I bought before. Just in case they are exhibiting the piezoelectric effect.

author: Melt-O-Tronic
author_rank: Frequent Contributor
timestamp: September 18, 2015, 07:11:28 pm
content: Since you have an SD slot on there, you should add a time logger function. Every 5 minutes, log the time . . . and time stamp each record.

author: marshallh
author_rank: Unknown
timestamp: September 18, 2015, 09:45:51 pm
content: Solved it, had the switching frequency set to 11khz, adjust RC timer for 72khz.

author: marshallh
author_rank: Unknown
timestamp: September 23, 2015, 07:58:09 pm
content: Secondary displays came (display alarm settings, wifi network, etc). They are alphanumeric

author: nidlaX
author_rank: Frequent Contributor
timestamp: September 24, 2015, 12:53:41 pm
content: Prop 65 warning, classic!

author: marshallh
author_rank: Unknown
timestamp: November 23, 2015, 03:07:26 am
content: "Colons" installed

author: TiN
author_rank: Super Contributor
timestamp: November 23, 2015, 04:07:23 am
content: Neat. Did you have fadein-fadeout for digit's change?

author: AF6LJ
author_rank: Unknown
timestamp: November 23, 2015, 04:31:27 am
content: That is way cool I love it.