Custom Nixie Tube Clock Review - Page 1
Forum section: electronics / projects

author: Evangelopoulos Panagiotis
author_rank: Contributor
timestamp: May 30, 2019, 07:35:28 am
content: Greetings,I've always wanted to make a nixie tube clock and recently I decided to take on the challenge and build my own. I've made countless prototypes before but this is the first time I'm gonnasend the PCB to a professional manufacturer and not make it my own. So I'd like it to be as perfect as possible so I can be sure that it will work first time since I don't have the money to re-print the PCB.I'll be driving each nixie tube separately since I don't want to fondle around with multiplexing. I'm using some K155ID1 nixie drivers and I'm driving those with a few daisy-chained 74HC595s to get the 36bit shift register that I need.Please review the schematic below and let me know if I have any major flaws that will mess my circuit up.Thank you in advance,E.P.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: May 30, 2019, 08:31:04 am
content: Looking goodI would be tempted toAdd a couple of LEDs to the D'sPut the switches on the A0...A3Bring out SQW from the DS3231 to a interrupt on change pinAdd either a ESP-01 socket for NTP sync or at least bring out RX to allow an external GPS module via a phono type socket.Finally when laying out the PCB make sure you size the current limiting resistors as you need prob 0805.Add a reverse protection diodeAdd a PTC fuseLooks funPSIt's hard to get it right first time, so use a cheap PCB place... I use elecrow because they have a cheap shipping option but use PCBShopper to find what is in your budget. (I was going to try JLPCB but their shipping options were too rich for me)

author: Evangelopoulos Panagiotis
author_rank: Contributor
timestamp: May 30, 2019, 09:21:45 am
content: Quote from: NivagSwerdna on May 30, 2019, 08:31:04 amThank you for your help!A few LEDs won't hurt indeed. Just for power indication or any other trouble-shooting stuff.I thought that only the digital pins of the Arduino had a built-in pull-up resistor but it seems that the analog pins do that as well. So I'llbring the switches over to A0-A3 so I can free up a few digital pins.I'm using a RTC module that does not have a SQW output but I'll put a one pin connector at D2 in case i want to use the interrupt pin in the future.Also thank you for the ESP-01 socket idea! It doesn't seem impossible that I'd want to make it wifi enabled at some point in the future!I'll add protection as well.I'll check those other two manufacturers as well since I was first thinking of JLCPCB.Thank you again for your help.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: May 30, 2019, 09:31:15 am
content: To be honest there isn't much to choose between A's and D's...Also some optional extras...Piezo for alarmAmbient light sensorDS18B20 temp sensorSome people also like neon colons between digits (Yuk!)RGB Backlighting LEDs (Hm)...If you do want NTP sync then an easy way to do this is to get a ESP module to fake a GPS message. So on the board you just need to provide switched 3V3 and level shifted RX. That way you also use an external GPS receiver too.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: May 30, 2019, 09:32:47 am
content: Quote from: EvangelopoulosPanagiotis on May 30, 2019, 09:21:45 amThe DS3231 can generate 1Hz on SQW which is useful since you then can be accurate to <1s with a simple interrupt. Use a pin that can do proper interrupts... D2? D3?

author: Evangelopoulos Panagiotis
author_rank: Contributor
timestamp: May 30, 2019, 09:47:31 am
content: Quote from: NivagSwerdna on May 30, 2019, 09:31:15 amCan I use Arduino's 3V3 output for the esp? Or should I put an external regulator? Another buck converter seems a bit of an overkill for just one module...I'll solder a small wire directly on the DS3231's SQW output and bring it over to D2

author: NivagSwerdna
author_rank: Super Contributor
timestamp: May 30, 2019, 10:10:56 am
content: Quote from: EvangelopoulosPanagiotis on May 30, 2019, 09:47:31 amIf you have 3V3 already then you are good... use that. I would add a P Mosfet (NDS332P?) to allow you to turn on and off ESP-01 power under uP control (That's what I do anyway... mine syncs once per day at 2am, running off the DS3231 during the day)

author: JackJones
author_rank: Regular Contributor
timestamp: May 30, 2019, 10:21:02 am
content: I'm not sure the 3V3 is able to provide enough current. The voltage seems to be provided by FT232R. The datasheet says you can get up to 50mA from the 3v3 it provides.https://www.ftdichip.com/Support/Documents/DataSheets/ICs/DS_FT232R.pdfThe ESP modules do take a sizable chunk of current, for example ESP-12F is listed at 80mA average here:https://www.elecrow.com/download/ESP-12F.pdfAlso don't forget the SQW is an open collector, you need a pullup resistor for it to work.Personally I think the ESP module might be a bit overkill. DS3231 is already 2ppm which translates to only a minute off per year.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: May 30, 2019, 10:28:54 am
content: Quote from: JackJones on May 30, 2019, 10:21:02 amI was only floating ideas. If the OP brings out switched 5V and RX in to an external connector then it could always be added later if required. ESP-01 and ESP-01 adapter cost peanuts on ebay.

author: Evangelopoulos Panagiotis
author_rank: Contributor
timestamp: May 30, 2019, 10:41:03 am
content: Quote from: NivagSwerdna on May 30, 2019, 10:10:56 amIs it possible to provide me with a schematic for that since i'm not sure how to drive the pmos?Quote from: JackJones on May 30, 2019, 10:21:02 amI'll use a MCP1811AT-033/TT on the 5V rail. 150mA should be enough.Quote from: JackJones on May 30, 2019, 10:21:02 amAh indeed. Will the built-in pull-up resistor of the digital pin work? Or should I add an external 10k?Quote from: NivagSwerdna on May 30, 2019, 10:28:54 amI'm not gonna use the ESP right away since the DS3231 is good at keeping time. But I'll add a connector in case I want to display weather info in the future.

author: BillyD
author_rank: Regular Contributor
timestamp: May 30, 2019, 11:07:14 am
content: This is not directly related to your schematic design as such, but might be useful to you.I built a couple of those nixie kit clocks fromhttps://www.pvelectronics.co.uk/index.php?main_page=index&cPath=21a few years ago and they came out very well.One of the things I really liked about their design was 'qtc' - quick change tube. So each nixie is mounted on a separate little board so you can easily test and swap them out without any difficult in-place soldering/desoldering.

author: Evangelopoulos Panagiotis
author_rank: Contributor
timestamp: May 30, 2019, 11:27:13 am
content: Quote from: BillyD on May 30, 2019, 11:07:14 amI'll be using IN-12Bs in socketsCause you never know when one will fail and you'll need to replace it. Also I'd be doing the same for the Nixie driver ICs since they are old and they could malfunction.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: May 30, 2019, 12:04:46 pm
content: Example (ignore the C if you already have some on the output side of your supply)

author: NivagSwerdna
author_rank: Super Contributor
timestamp: May 30, 2019, 12:11:40 pm
content: Quote from: EvangelopoulosPanagiotis on May 30, 2019, 10:41:03 amFWIW I have 10K pull-ups on the DS3231 output and I2C in mine....

author: Evangelopoulos Panagiotis
author_rank: Contributor
timestamp: May 30, 2019, 01:25:59 pm
content: Quote from: NivagSwerdna on May 30, 2019, 12:04:46 pmAwesome! Thank you so much for your help, feedback and ideas.This is the updated schematic that I think has everything I'll ever need.P.S. I saw that I cannot have multiple dot points being displayed at the same time since the driver does not allow multiple outputs to be enabled. But to be honest I doubt I'll ever have two dots on at the same timeand moreover I'm too lazy to build discrete transistor drivers for those.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: May 30, 2019, 02:06:36 pm
content: Cool. Please share some pictures when you have it working.

author: terminus
author_rank: Contributor
timestamp: May 31, 2019, 12:21:48 pm
content: I would replace arduino completely with the esp module. ESP-12 has enough gpios to operate the clock, much beefier than the nano and the board is smaller. You can flash arduino in it, but i prefer just C.My nixi clock prototype has ESP-12, 6 nixies in 2x3 mux (2 74hc595, 2 155ID1), i2c RTC + some sensors.

author: Skashkash
author_rank: Regular Contributor
timestamp: May 31, 2019, 01:33:21 pm
content: I also second the suggestion to use an ESP32. Lots of extra features. Easy enough to program within the Arduino framework.And you may want to sign up on the neonixe mail list. It's low traffic, but a lot of nixie enthusiasts (myself included) are subscribed. It's a good resource.https://groups.google.com/forum/#!forum/neonixie-l

author: NivagSwerdna
author_rank: Super Contributor
timestamp: May 31, 2019, 02:37:42 pm
content: I really should look at this too... the ESP32 has an RTC and deep sleep capability, so that might actually be accurate enough that you could ditch the DS3231 entirely and use infrequent NTP sync

author: schmitt trigger
author_rank: Super Contributor
timestamp: May 31, 2019, 02:54:51 pm
content: If you would like to complicate your circuit slightly but add significant appeal, I would add a Dekatron which rotates with the seconds.Dekatrons have 10 steps, so it would take 6 revolutions to complete a minute. But the rotating effect, in my opinion, is *far more appealing* than a plain blinking LED or neon.Another way to display the seconds, is to use a "magic eye", opening and closing in a heart-beat fashion. Again, very appealing visually.I have done both approaches.

author: Evangelopoulos Panagiotis
author_rank: Contributor
timestamp: May 31, 2019, 03:18:15 pm
content: Quote from: schmitt trigger on May 31, 2019, 02:54:51 pmThat actually sounds very very interesting! I'll keep it in mind for version 2 in the future! For now, since I'm using 8 displays I can actually display seconds, so I'll go with that option.

author: schmitt trigger
author_rank: Super Contributor
timestamp: May 31, 2019, 05:49:19 pm
content: May I suggest something then? Add the pads where you could connect a Dekatron or Magic eye circuitry in the future.The magic eye the simplest option. It can run from the exact same anode voltage that the Nixies use, and the drive can be accomplished with a pair of diodes, resistors and capacitors.The Dekatron is more interesting but more challenging. For starters, you require a voltage tripler on the output of your HV supply. The drive is bi-phase and requires some high voltage transistors.

author: Evangelopoulos Panagiotis
author_rank: Contributor
timestamp: June 21, 2019, 07:34:41 pm
content: Quote from: NivagSwerdna on May 30, 2019, 02:06:36 pmAnd it's alive!To my surprise it worked without any major problems. The HV power supply could use a bit of work but it works well enough.I ordered the PCB's from JLCPCB since it was the cheapest option. About 25 euro for 5 boards plus shipping. Not so bad...I know a lot of people are not fond of the black solder mask but I personally think it's the best. Looks super slick and it's more "presentable" than the others.I also ordered all components form LCSC, except for the NI-12Bs and a few other stuff.It was my first time soldering SMD so I got big resistor packages just to be sure.The code so far features:24h time display with the HH MM SS formatDate display with the DD MM YY formatThe ability to edit those valuesThe ability to store important values to the EEPROM in case the power is lostA "fun" display that shows the percentage of my life wastedAlso I made a quick cardboard base until I make the wooden enclosure I have in mind for this.

author: schmitt trigger
author_rank: Super Contributor
timestamp: June 22, 2019, 07:35:21 pm
content: Congrats!For this type of project, I also believe that a black solder mask was the best visual choice.

author: Macbeth
author_rank: Super Contributor
timestamp: June 22, 2019, 08:29:06 pm
content: Nice! Have you tested the DP's? You may want to add some resistors to them to limit current. I recall Dave used 100k on his Nixie subscriber counter.

author: Evangelopoulos Panagiotis
author_rank: Contributor
timestamp: June 22, 2019, 08:59:53 pm
content: Quote from: Macbeth on June 22, 2019, 08:29:06 pmTruth to be told I didn't pay too much attention to that.I thought the 22k for each tube would be sufficient. I'll check the current consumption and see if they draw too much power.So far the code does not allow a DP to be on if there is no digit displayed thus I hope that the current is somehow distributed based on the area of the cathode, creating a physical current limiter.Sadly enough I don't think there is enough space to fit 8 100k resistors without making it look horrible.So far they seem to work fine... Don't know if the extra current will burn them out quicker though.

author: Radiohead
author_rank: Contributor
timestamp: June 22, 2019, 09:33:51 pm
content: QuoteWhat problems do you have with the HV supply? It looks like you try to power quite a few nixies with the MC34063, eventhough you've included a darlington PNP transistor to boost the efficiency.I like the fact that you've outlined most IC's and added most component values in the silkscreen. It makes the PCB look quite nice without the components on the black silkscreen. (I'm used too getting PCB's without most silkscreen or designators due to size contraints, the massive amount of vias or designers lazyness)

author: Evangelopoulos Panagiotis
author_rank: Contributor
timestamp: June 22, 2019, 10:07:31 pm
content: Quote from: Radiohead on June 22, 2019, 09:33:51 pmYeah since I power a lot of tubes the ripple voltage is quite significant and the display flickers. Not so much that's annoying but a flicker non the less. Maybe the switching frequency is a bit low? The MOSFET runs quite cool but if you remove the output cap the MC34063 freaks out and the MOSFET overheats in seconds.In a future version I'm thinking of changing the HV PSU from a boost to a transformer based one. Either flyback topology or something else.For version one I'm surprised of how good it works.Detailed silckscreen is the best. I like seeing the values on the board as it also helps when debugging.

author: schmitt trigger
author_rank: Super Contributor
timestamp: June 23, 2019, 04:17:02 pm
content: What you could do, to require a lower step up ratio and a correspondingly lower duty cycle, is a diode-capacitor voltage tripler.For instance, if your Nixies require +180v, then you design your supply for +60v and allow the tripler to boost it.This tripler boost is not my idea, I picked it up from the website below. I had a circuit with both Nixies and Dekatrons, which require +510v anode voltage. It works flawlessly.Scroll down towards the bottom.https://threeneurons.wordpress.com/dekatron-stuff/

author: David Hess
author_rank: Super Contributor
timestamp: June 23, 2019, 07:51:45 pm
content: I would use common and inexpensive low voltage 1-of-10 decoders or the 74HC595 outputs without decoding to drive discrete cascode output transistors instead of rare 7441s or other integrated Nixie drivers. This would mean more wiring and parts though.