Questions: RF noise, double displays

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7 months 2 days ago #12418 by Alan7
Hi,

I just came across the Classic and All-in-one Nixie clocks. I’m considering building one for use in my amateur radio room. Two questions arise.

Considering the microcontroller and the switching supply, what degree of RF noise should I expect?

Can the circuit drive two 6-digit Nixie displays—or at least two hours displays? I’d like to display both local and UTC time. My initial thought is to parallel all anodes and cathodes of the minutes and seconds displays; hours cathodes would be driven by a second BCD to decimal decoder, with its BCD inputs either paralleled with the existing chip, or possibly driven by another four outputs from the microcontroller, if available. The first option would require a hardware solution to create the GMT offset and account for daylight saving. The second option could handle those issues in firmware.

Thanks for your input.
Alan

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7 months 2 days ago #12419 by Ty_Eeberfest
Hi Alan,

I'm not much of a radio guy but I'll tell you as much as I know. Hopefully one of the several hams who are members here will see your post and provide more info.

The boost converter doesn't run at a fixed frequency but rather is allowed to "wander" to achieve regulation. On my clocks, which are running on 12 volt power supplies, the converters run somewhere around 40KHz. Changing the input voltage will likely change the frequency significantly.

There is definitely some noise being radiated. I have no equipment to properly measure it so I did the next best thing - set a super cheapo portable received next to the clock. Said receiver has "LW" (144 - 180KHz), "MW" (AM broadcast 540 - 1600KHz) and "SW" (5 - 15MHz) bands plus FM broadcast. The clock is blasting out interference (harsh tone that I assume is a harmonic of the switching frequency) all across the "LW" band for a distance of about 2 - 3 meters. All other bands were unaffected. Does anybody do anything down in that "LW" band?

In regard to multiple displays, the HV boost converter will not drive multiple displays, It simply doesn't have the oomph to do that. By far the simplest solution would be to get 2 clock kits. Alternatively you could do as you described using 1 kit and disable its boost converter. If disabled correctly there's nothing to stop you from feeding in your own HV from a beefier external 170VDC power supply.

Look into it later when the dust is clearing off the crater.

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7 months 2 days ago - 7 months 2 days ago #12420 by BS_Jim
Hi Alan,

KB2LDO, Jim here. I hadn't hooked up my radios in a while, so I put my 10m radio next to the clock and hung a 6' piece of wire out of the antenna jack. The clock is pretty quiet. It does add some noise but not enough to wake up the S-meter. I think if your antenna is any distance from your clock it wouldn't be noticeable, or at least not a problem.

I don't think the clock board could drive 2 displays comfortably without adding an external HV supply or at least using a beefier FET w/ heatsink and beefier 9v or 12v supply. I would think that the path of least resistance here would be to build 2 complete clocks and put them both in the same enclosure. They're pretty inexpensive, I doubt the EMI would give you problems, and it would give you the most flexibility,

Jim

Edit: Ty beat me to it. Haha
Last edit: 7 months 2 days ago by BS_Jim.

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7 months 2 days ago #12421 by Ty_Eeberfest
An afterthought: with the 2 clock approach it is highly unlikely that the clocks will run in perfect sync. Even with WiFi modules for NTP sync, or RTC modules, the best you can expect is for them to be within 1 second of each other. 2 non-synchronized displays in one enclosure would drive me nuts, while some people might not mind it at all.

I can see how with some hardware and firmware fiddling the clocks could be held in much tighter sync, probably by utilizing the I2C bus. I haven't really thought this through yet...

Look into it later when the dust is clearing off the crater.

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7 months 2 days ago - 7 months 2 days ago #12422 by BS_Jim
True. Maybe if you built one 6-digit clock and one 4-digit clock you could alleviate the problem.
Last edit: 7 months 2 days ago by BS_Jim.

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7 months 3 hours ago #12444 by Alan7
Thank you all for your very helpful responses, especially for taking the time to empirically research potential EMI/RFI.

You did anticipate a couple of my thoughts. One, that two separate clocks would not quite sync and would drive me nuts. Two, that the 170V supply (probably) would not have the capacity to drive dual displays.

I have two surplus power transformers for vintage Heathkit Nixie equipment. I had already thought about bypassing the switching supply, instead building a vintage linear 170V supply. That should solve two potential problems. If the controller has the fanout capacity to drive two BCD to decimal decoders, I should be set. It's been a long time since I've experimented with digital circuitry, 4000-series CMOS, never got into microcontrollers. Too many other things to do in those days.

It's sort of silly to build the dual display anyway, but the UTC offset is another little thing that drives me nuts. Five hours, six hours, daylight time or not...which one is it today?

Thanks again!
Alan

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