Nixie Clock - Page 1
Forum section: electronics / projects

author: DotComBoy
author_rank: Contributor
timestamp: September 11, 2012, 01:04:24 am
content: Hey guys, this is my first real project.Since i started watching Dave´s blog, it inspired me to try to build something my self.I got some in-12a nixie tubes with 74141 controllers and i thought about using them to build a clock with RTC and some nice enclosure.I´m not very good in Eagle but i´m tryingBelow is how the schematic look so far. Any sugestions?

author: David_AVD
author_rank: Super Contributor
timestamp: September 11, 2012, 02:02:37 am
content: How do you set the time?

author: DotComBoy
author_rank: Contributor
timestamp: September 11, 2012, 02:06:51 am
content: I still haven´t decide about using resistor ladder DAC or just simple switches. i think simple switches it will be..

author: DotComBoy
author_rank: Contributor
timestamp: September 11, 2012, 02:11:57 am
content: There we go..

author: David_AVD
author_rank: Super Contributor
timestamp: September 11, 2012, 02:19:17 am
content: I gather the power supply for the logic is not shown? Nixie tubes need heater voltage too don't they?

author: GK
author_rank: Super Contributor
timestamp: September 11, 2012, 02:19:29 am
content: I'm afraid that using IC's, let alone a micro controller for a project like this is cheating.

author: GK
author_rank: Super Contributor
timestamp: September 11, 2012, 02:20:07 am
content: Quote from: David_AVD on September 11, 2012, 02:19:17 amNo, they are just neons.

author: David_AVD
author_rank: Super Contributor
timestamp: September 11, 2012, 02:21:32 am
content: Ah, just a HV source then (apart from the logic supply).

author: DotComBoy
author_rank: Contributor
timestamp: September 11, 2012, 02:24:16 am
content: Quote from: GK on September 11, 2012, 02:19:29 amI choose not to multiplex the tubes because i think it may shorten it´s lifetime.Quote from: David_AVD on September 11, 2012, 02:19:17 amPower supply is not shown, but probably it will be 7805 + caps for the Atmega and a HV module that i have for the tubes.

author: GK
author_rank: Super Contributor
timestamp: September 11, 2012, 02:41:31 am
content: Quote from: DotComBoy on September 11, 2012, 02:24:16 amNnnooooooooo.........I mean IC's altogether.......I designed an alarm clock as an apprentice tech without IC's, full schematic prints out onto about 20 A4 pages, 800 odd transistors. Now some 12 years later I am finally getting around to building it:http://www.users.on.net/~glenk/ddac/ddac.htm

author: GK
author_rank: Super Contributor
timestamp: September 11, 2012, 02:45:09 am
content: BTW, clocking from the mains frequency in your design will have better long term accuracy than the RTC.

author: mariush
author_rank: Super Contributor
timestamp: September 11, 2012, 03:33:24 am
content: For such a simple project, I think you could drop the external oscillator and capacitors and save about half a dollar. The internal oscillator will have enough precision for a watch, it will only update the display several times a second at best so you don't need much precision.Add decoupling capacitors between Vcc and GND .. 0.1 - 0.47 will be fine. The DS1307 would like one as well.

author: GK
author_rank: Super Contributor
timestamp: September 11, 2012, 04:24:43 am
content: The RTC makes for a cheap and easilly implemented battery backup. Nothing more annoying than having to reset a clock after a brief power interruption.Crystal oscillators do have to be very accurate for long term accuracy in clocks. An frequency error of 100ppm will work out to about 1 minute of error per week; approximately half an hour in six months. I wouldn't rely on the untrimmed uC oscillator for this application.

author: mariush
author_rank: Super Contributor
timestamp: September 11, 2012, 04:41:05 am
content: It seems to me he's reading the time from the RTC, which has its own independent oscillator. I was talking about the external 16 Mhz oscillator attached to the Atmega.That Atmega as far as I can tell from datasheets at a summary glance works at 1-4 Mhz using the internal RC oscillator. I think he doesn't need more than 1 Mhz to loop several times a second reading the time from the RTC and flipping some bits on the output pins.If he reads the time from RTC ten times a second, in the worst case scenario where the atmega slowly drifts the updates on the nixie screen within 50 ms from the desired refresh moment.

author: DotComBoy
author_rank: Contributor
timestamp: September 11, 2012, 08:59:55 pm
content: Quote from: mariush on September 11, 2012, 04:41:05 amQuote from: mariush on September 11, 2012, 03:33:24 amSince i´ll be using Arduino plataform for development, seams easier to me just to use the crystal, and because this won´t go in mass production, $1 or $2 won´t make a lot of diference, but is something to think about for the future, thanks.Will add the decoup caps, thanksQuote from: GK on September 11, 2012, 02:41:31 amit was my first idea, but because my idea is to learn more about uC, i choose the atmega..Besides that, with the uC the project will be ready earlier( i hope )

author: DotComBoy
author_rank: Contributor
timestamp: January 14, 2013, 12:57:30 am
content: Hey guys, long time without messing with electronics.Since a few components arrived i built in the breadboard this HV power supply for the display:http://slacklist.olek.waw.pl/smietnik/nixie2/zasilanie/nixie_supply.pdfand worked like a charm.To improve my learning, i draw the schematic in eagle(bellow), routed the board and assembled.the problem is that after turning on, the display turn on for aprox. 30seconds and then the inductor blows out.Is there any mistake i did that i´m not seeing?

author: cwalex
author_rank: Frequent Contributor
timestamp: January 14, 2013, 01:53:07 am
content: are you using a power inductor or one of those ones that looks like a through hole resister but fatter? I think the latter will blow up in that circuit.#disclaimer: I'm a beginner and take my advice with that in mind

author: DotComBoy
author_rank: Contributor
timestamp: January 14, 2013, 02:01:30 am
content: i´ve tried the one that looks like resistor and another in a plastic case, both worked in the breadboard but blew in the pcb after a few seconds.

author: cwalex
author_rank: Frequent Contributor
timestamp: January 14, 2013, 03:08:02 am
content: Quote from: DotComBoy on January 14, 2013, 02:01:30 amThat's weird! have you triple checked your PCB layout is correct?

author: A Hellene
author_rank: Frequent Contributor
timestamp: January 14, 2013, 03:30:06 am
content: This is not an entry-level project! Apparently, you will have to do some serious homework in order to become able to create designs that work as expected. Fortunately, every little detail of thatblack artis out there, awaiting to be accessed, learned, combined and internalised. Do not be afraid to look up the terms that you think you understand; there is always something more to learn about anything, and the little details are always the ones that can really make a difference.Anyway, this is not onlyan excellent tutorialon the Nixie Clock project you are building; it is an extremely detailed teaching course, written by a brilliant author, on the use of high-voltage DC-DC converters, inductors and drivers, RTCs and of all the other project subsystems as well as the use of the microcontroller itself, with schematics, source code and references most of the textbooks would not even dream of touching!And, yes, a single "anaemic" m48 microcontroller can easily run everything!As a side note, do never think of the mains power supply as an accurate frequency reference.It is not!-George

author: c4757p
author_rank: Super Contributor
timestamp: January 14, 2013, 05:07:19 am
content: Can I offer some friendly criticism?BIG pet peeve: don't use text labels as links unless youreallymust. It's much easier to read your schematic if you draw every wire. Some of them are pretty bad - pin 3 on the 555 shouldn't be labelled "out" for example, it suggests that it's the circuit output. Something like "drive" would be better. (It is a good idea on more complicated schematics to keep the labelsandthe wires - use them to mark wires, not make connections.)Straighten up the funny corners like above the MOSFET.General layout orientation is left-right=input-output, top-bottom=positive-negative. Basically, a horizontal flip of the whole schematic (the 555 is on the "input"), and move the MOSFET so ground/source are at the bottom.More general layout: If it's desirable that things be physically close together (like C2 and L1), put them together on the schematic. Keep short wires short (no need to run all the way around the 555 to connect 6 to 2), and it makes more sense visually to connect R5 (for example) to the VCC port on the 555 rather than the one on the inductor. Electrically the same, logicallynot.I've built this circuit before. Oneimportantfundamental problem: if the trimmer's wiper comes off the track, the control loop is disconnected and it flies up towards the maximum output voltage.Notgood, it's capable of quite a bit depending on the component values. I have used a similar circuit to supply 20W at 350V! You should include a second voltage control system (the two resistors, potentiometer, and BC547), but with a fixed voltage (no trimmer) a bit higher than the highest you will use this at. (Work out the resistor values with Ohm's law, keeping the total resistance above around 200k, so that you get around 0.65-0.7V on the transistor's base at the desired output voltage). You want enough margin that you don't need a trimmer.Test it- not just by disconnecting the trimmer and actually causing a fault, since depending on the voltage it could blow up the capacitor or something else awful, but by changing the values on the trimmer circuit so you can adjust the voltage too high, start out low, and gently bring it up, making sure it hits a ceiling at the right spot.I'm a bit safety obsessed when I design things like this - this might be a bit unnecessary - but instead of that, I might include a latching overvoltage shutdown above a certain voltage. A similar circuit to the feedback one, switching a latch (you can build one with two transistors, Google "two transistor latch"), pulling down the reset pin through a resistor. I'd even consider having the latch blow a fuse so it stays permanently shut down until inspected.Are you really using IRF512, or is that just for convenience out of the components library? It's only rated 100V! I haven't used Eagle but I bet you can change the component value so it's clear.Hint: T1 (BC547) can be pretty much any general-purpose NPN signal transistor, so don't go out and buy a bunch of BC547s if you don't already have some.I understand the "DIY" appeal of using just a 555, but you'll get much better characteristics with a part for the purpose - I've used UC3843 with good results, for example, and there are many others. Alternatively you could drive the thing with the microcontroller's PWM output, though you have to be a bit more careful about duty cycle since you don't have such a nice, easy analog feedback loop. Though this circuit does work for the purpose, if you like it.The feedback loop will have a good amount of dependency on the input voltage, though it might not be obvious at first. I've seen 50V variation on the output over 9-16V in. I'd power at least R6 and the 555 through a regulator to avoid that (or redesign the feedback loop not to depend on it so much). Do not power the inductor through the regulator, it's a big waste.Connectors: You probably shouldn't have your HV output sharing a connector withanything, much less the VCC that probably goes off to other circuit boards that might have human interface stuff on them! Pay special attention in general to keeping the HV away from humans, even if components fail. Safety standards are generally better these days than in the Nixie tube era, and this is one place where the appeal of doing things the old-fashioned way might not be worth it.Sorry, I know it's a lot and some is a bit nit-picky, but it's always good to improveAttached is how I would draw it, though it could possibly be tidied up a bit more.

author: kizzap
author_rank: Unknown
timestamp: January 14, 2013, 05:26:59 am
content: Quote from: DotComBoy on January 14, 2013, 02:01:30 amThis may sound like a silly question, but were you loading the circuit, or just measuring the voltage output?

author: jnd
author_rank: Regular Contributor
timestamp: January 14, 2013, 09:42:44 am
content: Quote from: GK on September 11, 2012, 02:41:31 amOh come on, you're using brand new components? That's cheating. You should use NOS, at least 20 years old components, preferably metal and ceramic packages, no cheap TO-92s! You can use ICs that way too but only from that era, like 8048 mcu.

author: svofski
author_rank: Regular Contributor
timestamp: January 14, 2013, 10:34:19 am
content: Quote from: DotComBoy on September 11, 2012, 02:24:16 amI do not know, why do you think so? This is the first time I hear of this. If anything, it might prolong the life because the current through the nixies will be lower.Generic thoughts — you seem to like to have many parts in your circuit. It is really easier to take a higher pin count uC than to use 2 external shift registers. It is also easier to multiplex the top side and use only one decoder at the low side: that way you can stay with the same pin count and without 2 extra registers.Not sure if this was already said before, but you need to carefully select the MOSFET for the boost converter. There are many very good MOSFETs that would not open from +5V. I had good success with IRF630N, from 5V TTL level they open just enough and they're fairly robust. Using a driver is still not a bad idea imo.How are you going to regulate the duty cycle of your 555-driven converter? You have a micro that can provide rock stable signal with adjustable frequency and duty cycle entirely in hardware, without any CPU interaction. It also has ADC which can be used for feedback. Why not use what you have?My nixieclocks:Patashnik(non multiplexed, Mega8535),Satashnik(multiplexed, Mega8). The latter is probably as minimalistic as it gets.

author: c4757p
author_rank: Super Contributor
timestamp: January 14, 2013, 12:16:46 pm
content: Quote from: svofski on January 14, 2013, 10:34:19 amI've heard this a few times, though I haven't actually seen any evidence. People seem to think that the breakdown process that strikes the tube in the first place is damaging to it, so it's better to only strike it when changing digits than to flicker it many times a second. My hunch is that this is bullshit, considering neon lamps happily operate on AC all the time as pilot lights. I don't have that much experience with neon lamps, but in my limited experience, I've yet to see one burnt out.QuoteThe feedback circuit connected to the CV pin does this. It's nottruePWM - the frequency changes as well - but I've used a very similar circuit a few times and it does a decent job of regulation.

author: Ketturi
author_rank: Regular Contributor
timestamp: January 14, 2013, 12:27:49 pm
content: Nah, I think its ok to mix old and new tech, if outcome is something new looking or there is no need to show internals to everybody. Restoring old devices are different thing. And building nixie clock is definitely beginner project, but as project it is very rewarding and educational. I too have clock project (can be found fromketturi.kapsi.fi) which is very similar to this. RTC is probably easier than using avr to keep clock, and accuracy is better and battery backup can be done straight to rtc ic as said in replies. AVRs internal RC oscillators are horrible to even serial communication.Quote from: DotComBoy on September 11, 2012, 02:24:16 amI have heard about this too, I don't know if its true, but I also choose not to multiplex. Does someone knows is there any proof like measurements and tests?Also messing around with HV is not good thing, I would stay using off-the-shelf nixie power supplies, and even with them there is chance to blow everything up like I did. I wouldn't try to use main micro to generate voltage, what if feedback fails and voltage shoots over ruining tubes with arc or programing bug causes something horrible like shooting fatal radiation out of tubes ;3

author: c4757p
author_rank: Super Contributor
timestamp: January 14, 2013, 12:51:47 pm
content: Quote from: Ketturi on January 14, 2013, 12:27:49 pmI think it is always important when working with dangerous voltages to have some sort of analog control loop that does not depend on a clocked microcontroller, but this can be very simple and just for the purpose of a shutdown. The whole converter doesn't need to be part of it. Just have it sense a "too high" voltage and somehow shut the whole thing down (interrupt the gate drive, power down the micro, whatever is convenient depending on the circuit). Hell, if you're not feeling particularly subtle, you could power the inductor through a fuse and have a crowbar just short it out and blow the fuse.Also, I'm pretty sure a boost converter that's powering Nixies is nowhere near capable of "fatal radiation". 170V (I'm guessing, too lazy to go back and check...) is definitely a shock hazard, but so is 40V. It isnot"HV", though I've been using the term myself. It's not going to make X-rays, it's not going to arc across spectacular distances, it's not going capacitively couple through glass (think those plasma globe thingies - you can draw a good spark off a piece of foil set on the top), blah blah blah. Just don't touch it and don't exceed component ratings. However, the precautions you take when playing with circuits like this are yours and yours only, you should make damn sure nobody else who uses your circuit has to take them as well. Pretend it's 100kV when you're designing anything that comes near the operator.

author: svofski
author_rank: Regular Contributor
timestamp: January 14, 2013, 01:02:02 pm
content: QuoteWell if your multiplexing is THAT slow, maybe. But it's not like the ionisation goes away the very instant you switch off the current. They do not have to "srike" every cycle. But even if they had to, how is that reducing their lifetime? I do not know.QuoteI have two Nixie clocks that are always on for 3 years already. One is multiplexed, another is not but runs at 1/4 duty cycle (if memory serves). Both look like new. I've been told by smart people that they're going to wear out after 1 year. For when they finally will have decied to agree with the smart people, I have another nixie clock waiting for its turnQuoteIf the feedback fails in the micro, that means probably that it is either fully dead == not generating any PWM, safe, or if it still lives, it would be a failure caught by the WDT == full reset, safe. Well, it should not happen -- test your code well.My converters are set to about 180V, their theoretical limit is 200V because of the breakdown voltage of the MOSFET. If your simple boost converter is capable of producing enough to make your tubes arc and emit X-rays, I need your circuitP.S. Touching a boost converter is very much not recommended, I tried.

author: c4757p
author_rank: Super Contributor
timestamp: January 14, 2013, 02:20:11 pm
content: Quote from: svofski on January 14, 2013, 01:02:02 pmGood point, I never really think about that. Are you sure that it will really break down at that voltage, though, or is it just guaranteednotto break downunderit? I've never considered a FET's D-S breakdown to be something to depend on.

author: Ketturi
author_rank: Regular Contributor
timestamp: January 14, 2013, 02:32:03 pm
content: Quote from: svofski on January 14, 2013, 01:02:02 pmQuote from: c4757p on January 14, 2013, 12:51:47 pmAnd I tough it was obvious jokeYeah probably it would not exceed over 200V in any circumstance of software failure, but you can't be never too sure. And neon tubes can arc internally, which probably would break them. Also too high voltage means bigger current, and tubes wear much faster. Nixie clock always should be enclosed well if other people are using it. I would use same shielding standards as commercial wall powered appliances if I built it to someone else.

author: DotComBoy
author_rank: Contributor
timestamp: January 14, 2013, 04:09:51 pm
content: Hey guys, thank you very much for the help.Quote from: A Hellene on January 14, 2013, 03:30:06 amI´ll definitely take a look on it, thanks.For me is hard to start with simple circuits, because i keep thinking ahead, and when i see it its already a huge project, i have tons of projects in my head, all of them startet with a simple thing such as lamp dimmer, and in my mind become a complete house automation system.thats why i can´t never get any thing done.Quote from: c4757p on January 14, 2013, 05:07:19 amFriendly criticism is always welcome, i think thats why forum existsNotedNotedNotedWill do, i have some difficult to use crossing lines that are not connected, need to change thatthe second transistor base in parallel with the first?Will have to study this more, don´t really understand.I´m Using IRF740, just didn´t find on the libary, so used a similar one,i have a bunch of those,I´m actualy building this one because i found the easiest one, with components that i could easily find near home, i hate brazilian post service, it take a month for me to recieve orders, so i tend to use more common components, AND.. i´m kind of new in uC too, so i think like this the learning curve wiill be easiera LM7809 will do right?will use two connectors thenQuote from: kizzap on January 14, 2013, 05:26:59 ami´m loading with a nixie tube and a 22k resistorQuote from: cwalex on January 14, 2013, 03:08:02 amyes, actually i did find a flaw in the design, there were 2 ground planes that weren´t connected, fixed, but the problem started after this.

author: c4757p
author_rank: Super Contributor
timestamp: January 14, 2013, 05:05:51 pm
content: Quote from: Ketturi on January 14, 2013, 02:32:03 pmI see that now, sorry

author: c4757p
author_rank: Super Contributor
timestamp: January 14, 2013, 05:08:20 pm
content: 5. No, the collectors both pulling down pin 5 (CV). Emitters both to ground, and each base to its respective voltage divider.6. That's OK, it's overkill. Just make sure you understand the converter itself so you don't do anything ridiculous.10. Yup, that's fine.

author: svofski
author_rank: Regular Contributor
timestamp: January 14, 2013, 06:32:19 pm
content: Quote from: c4757p on January 14, 2013, 02:20:11 pmWhat I was going to say is that if your FET breakdown voltage is 200V and it does not break immediately, it means that your boost converter will never exceed 200V at its output. The voltage at output ~ the highest peak you can get on the drain when the MOSFET closes.

author: DotComBoy
author_rank: Contributor
timestamp: January 14, 2013, 08:48:33 pm
content: looking better?

author: mark-r
author_rank: Contributor
timestamp: January 14, 2013, 09:27:10 pm
content: Quote from: GK on September 11, 2012, 02:19:29 amI think the 7441 / 74141 is allowed - it was specifically designed to drive Nixies and dates from the same era. I guess for absolute accuracy you could try to source NOS parts with 60s date codes!

author: c4757p
author_rank: Super Contributor
timestamp: January 15, 2013, 04:38:22 am
content: Yeah, it's looking better. Don't forget to connect pins 6 and 2, and the HV output to the connector (it doesn't look like you've labelled the actual output, so they aren't connected).

author: DotComBoy
author_rank: Contributor
timestamp: January 15, 2013, 11:55:17 am
content: Quote from: c4757p on January 15, 2013, 04:38:22 amthey were named but forgot to label it.

author: DotComBoy
author_rank: Contributor
timestamp: January 15, 2013, 03:48:53 pm
content: If i already have C4, do i really need the filtering cap C5 in the 7809 input?

author: DotComBoy
author_rank: Contributor
timestamp: January 15, 2013, 04:11:04 pm
content: How does the board looks?

author: svofski
author_rank: Regular Contributor
timestamp: January 15, 2013, 04:47:50 pm
content: That L1 looks impossibly small to me.

author: DotComBoy
author_rank: Contributor
timestamp: January 15, 2013, 04:55:29 pm
content: they look like resistor.can´t use those?

author: svofski
author_rank: Regular Contributor
timestamp: January 15, 2013, 04:58:10 pm
content: No idea, what current they're rated for? Are they really 100uH?

author: DotComBoy
author_rank: Contributor
timestamp: January 15, 2013, 05:01:13 pm
content: these one:http://www.futurlec.com/Components_Others/IND100.shtml

author: svofski
author_rank: Regular Contributor
timestamp: January 15, 2013, 05:08:16 pm
content: I see.. npi about those tiny ones. I think you should be looking at this page:http://www.futurlec.com/Power_Inductors.shtml100µH 2.1A Power Inductor is looking good enough.

author: DotComBoy
author_rank: Contributor
timestamp: January 15, 2013, 05:14:02 pm
content: Dammm.. one month to recieve the componets again ;/

author: DotComBoy
author_rank: Contributor
timestamp: January 15, 2013, 05:19:04 pm
content: Besides L1, how the rest looks like?

author: svofski
author_rank: Regular Contributor
timestamp: January 15, 2013, 06:42:47 pm
content: No need to wait 1 month for a choke. You can salvage one from junk electronics. Look around you. Old printer boards have some, ATX power supplies, CCFL lightbulbs. If you have a ferrite core, wind the choke yourself — just do not use wire that is too thin. You do not really need a precise value here, anything around 100uH is good enough.As for the board:It's been said already, but IRF512 is not suitable for your task because it has low breakdown voltage. You need IRF630N or the like.You want C4 to be as close to the choke/drain as possible, on your board it's stashed in a faraway corner.Try to trace a path from the Source of your transistor to the power supply connector. It's a long and twisty passage. It should be as short and as broad as posible.I'm not sure if C6 needs to be that huge. 1uF sounds about right but 1uF/16V is usually a rather small package.C3 on the contrary has to be rated at least for 250V and if possible be a low ESR type ("designed for flash" in datasheet). The low-ESR is not critical here but the package looks small to me anyway.I would try to put R4/C2 in such a way that their ground is somewhere on the same path with the main ground return path from the MOSFET source.I would probably double or even quadruple the feedback divider values to reduce the unnecessary losses there: you're going to radiate ~0.2W on your feedback loop alone. Not sure about 1K trimpot there, wouldn't it make a very narrow adjustment range? I think a single-turn trimpot would suffice for this job, but it's ok if you have a suitable multiturn trimpot.You can simulate this circuit in Circuitlab or LTSpice BTW, at least the feedback part should simulate well.

author: DotComBoy
author_rank: Contributor
timestamp: January 15, 2013, 07:29:31 pm
content: Will be using IRF740, just forgot to change the name before taking the screenshotC4 closer to choke nowPath is more straigh forward now, right?C6 is smaller nowi´ll check the cap size i have at home, in the other board i made seams to work. it´s not low ESR though.Got C2/R4 closerQuote from: svofski on January 15, 2013, 06:42:47 pm

author: svofski
author_rank: Regular Contributor
timestamp: January 15, 2013, 09:21:27 pm
content: The ground return path still forms a long whip all around the board. It will work but you're making a broadband radio jammerIf you moved Q1 inwards by a few millimeters you would have a much shorter ground return path around the left edge of the board, but there still going to be a loop. I don't know.. If I was doing this I would try to group the high-current parts close to the power supply input so that there would be no problems like this.

author: perfect_disturbance
author_rank: Regular Contributor
timestamp: January 16, 2013, 03:21:14 am
content: Quote from: GK on September 11, 2012, 02:45:09 ammains frequency is OK but you'll have better long term accuracy if you have tune a radio to wwvb.

author: GK
author_rank: Super Contributor
timestamp: January 16, 2013, 11:14:26 pm
content: Quote from: perfect_disturbance on January 16, 2013, 03:21:14 amA cheap GPS module is the go these days.

author: svofski
author_rank: Regular Contributor
timestamp: January 17, 2013, 09:33:16 am
content: I use DS3234 — those things are ridiculously accurate in the long term.

author: jeroen74
author_rank: Frequent Contributor
timestamp: January 17, 2013, 02:13:47 pm
content: A GPS module likely does not lock on indoors.You could roll your own tempco compensation of a watch crystal, TI has an appnote on this. And with a bit of cleverness you can run the MCU from a battery during mains brownouts.

author: GK
author_rank: Super Contributor
timestamp: January 18, 2013, 02:23:15 am
content: Quote from: jeroen74 on January 17, 2013, 02:13:47 pmLikely not, but an outdoor GPS antenna is a lot less inconvenient than a HF dipole for WWV!

author: jeroen74
author_rank: Frequent Contributor
timestamp: January 18, 2013, 10:54:46 am
content: If I'm not mistaken GPS time is UTC with a 16 sec offset. And GPS modules contain their own battery/capacitor backed up RTC so that's one headache less too.

author: svofski
author_rank: Regular Contributor
timestamp: January 18, 2013, 12:13:52 pm
content: Quote from: GK on January 18, 2013, 02:23:15 amWhat it was the last time when you have seen a radio clock with a dipole? Not sure about the Americas, but in Europe MSF and DCF77 work on very low frequencies (60kHz and 77.5kHz) and the receiver modules are very compact: just a ferrite wound antenna and a baseband mixing receiver with a crystal. The signal from Germany and UK is strong enough to be received here in St.Pete but probably only during the quiet nights.There is only one potential problem though, I'm not sure if sensitive radio receivers and switchmode power supplies can be good friends.

author: GK
author_rank: Super Contributor
timestamp: January 19, 2013, 01:08:20 am
content: Quote from: svofski on January 18, 2013, 12:13:52 pmWell, I have a a couple of obsolete and gutted HF radio chronographs sitting under my bench. Salvaged a bunch of really rare neon decade indicator tubes from one too. In seismology, our department used to run a dozen of them or so. No all of our stations are GPS, which now is the universal standard for accurate seismological timekeeping. perfect_disturbance mentioned WWV; for that, down here at least, you some form external of a HF antenna for reliable reception. The plug was pulled on our VNG years ago.

author: David_AVD
author_rank: Super Contributor
timestamp: January 19, 2013, 05:28:13 am
content: I've just been playing (indoors, about 3m from window) with a Parallax 28501 GPS module and it is using 6 of 11 satellites at present.When I had the 28502 external antenna on the window sill, it was using 7 of 11 satellites.It does jump around from 6-8 out of 10-12 (used/found) with either the internal or external antenna.

author: svofski
author_rank: Regular Contributor
timestamp: January 19, 2013, 10:57:01 am
content: But you did not tell us what material is your roof made fromWell, here in the north GPS is generally weaker and the error is higher. And in my heavy brick house I do not see many satellites 3m from the window. Lucky if I see any on the windowboard.

author: SeanB
author_rank: Super Contributor
timestamp: January 19, 2013, 11:11:19 am
content: Turned on the GPS module on the windowsill. Took 2 minutes before it got a time signal ( what I use it for, as a backup to NTP for the current time) and currently has 3 satellites in view. Have not turned it on for about 3 months, and it does not have an internal battery ( I took the internal Nokia clone battery for use elsewhere when I bought it) to store data anyhow. Cheap $10 bluetooth module ( never used bluetooth side) running into a somewhat modified Nokia serial clone cable.

author: David_AVD
author_rank: Super Contributor
timestamp: January 19, 2013, 12:18:52 pm
content: Quote from: svofski on January 19, 2013, 10:57:01 amBrick walls and concrete tile roof.

author: svofski
author_rank: Regular Contributor
timestamp: January 19, 2013, 06:11:39 pm
content: Quote from: David_AVD on January 19, 2013, 12:18:52 pmIn that case in your region GPS reception must be much stronger than here. Or maybe the modules in the phones are weaker, I'm not sure — I only have a couple of Android phones to try this. It's been about 10 minutes since I launched GPS monitor at ~2.5m from the window and no signs of any kind of signal.

author: jeroen74
author_rank: Frequent Contributor
timestamp: January 19, 2013, 06:24:39 pm
content: I have a Fastrax UP500 module, it barely locks on indoors, but it depends on the exact location.

author: David_AVD
author_rank: Super Contributor
timestamp: January 19, 2013, 10:33:37 pm
content: Taken approx 8:30 am with just the on-board patch antenna and 4 metres in from the house roof line.