Precision clock Mk IV questions

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jonas	Posted: 27 Jun 2025, 12:21 PM
Member Posts: 8 Joined: 29-May 25	Hi there, finally managed to get my IV kit from the customs and immediately assembled it. I have two questions – when set to "toggle mode" I noticed that the timing of the colons is not very precise on the mkII1/2 when compared to mkIV. Or at least it "seems" that way: https://www.dropbox.com/t/uwLZLV8BJ1p4KVEv Is this expected? Second question – I lost the cable protecting acetate cutout somewhere, is there a way to get a dxf or svg file so I can cut out my own? (I have a laser cutter available) Thanks for doing these, love 'em! -------------
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mit	Posted: 27 Jun 2025, 03:05 PM
yeah whatever Admin Posts: 629 Joined: 4-May 16	The Mk III uses the colons to indicate debug data about the oscillator discipline. I originally did this in order to monitor/develop the firmware, but ended up leaving it in. Depending on if the oscillator is fast or slow, it adds a 100ms delay to the colon blink. The loop can take a while to lock, so it's nice to be able to look at the clock and see that it's alternating fast and slow, which means it's locked. When it first gets a fix, it might stay fast or slow for a minute or so before aligning. The Mk IV just has an animation, which I've arbitrarily aligned to the second, no debug data. But the onboard TCXO means there's no need to discipline the main oscillator. It does perform a slow calibration of the RTC though, for when the clock is turned off, and there's a debug mode than can show some info about it, but the RTC crystal is temperature sensitive so it'll never keep time that well. Laser-cut files are in the repo, but unfortunately they're in moshidraw format. One of my tasks is to convert or re-draw them in a sensible format, I'll get round to that soon. -------------
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mit	Posted: 29 Jun 2025, 05:07 PM
yeah whatever Admin Posts: 629 Joined: 4-May 16	I've created an SVG version of the laser cutter files and stuck it in the repo: https://raw.githubusercontent.com/mitxela/clock4/refs/heads/master/cad/hinge.svg Moshidraw has this terrible habit of converting arcs into polylines which makes it hard to know exactly what the original radius and centre were, so the redrawn version of the acetate might not match exactly, but it should be close enough to work. For laser cutting acetate the best technique is to sandwich it between two pieces of soaking wet paper. This stops the edges from fraying and turning brown. -------------
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jonas	Posted: 30 Jun 2025, 09:33 AM
Member Posts: 8 Joined: 29-May 25	Thank you very much for the help! I spent like an hour trying to find that piece. I am sure it was in the kit, but I just lost it somewhere. Is there a way to make the blink on MKIII regular? I am planning to use it in an art installation. Thanks again! -------------
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Grumpsimus	Posted: 11 Jul 2025, 02:21 PM
Member Posts: 4 Joined: 10-July 25	I haven't got Mk IV yet, still waiting. However, the one thing that I will really miss is the timezone markers for GMT, BST etc, these are a pretty unique feature for any clock. I hope that they can be reinstated for the Mk V. This got me thinking about what time is being displayed? It appears to be GPS time. Because there are no leap seconds in GPS time, it is now 18 seconds differeny from UTC. Maybe you could clarify this? -------------
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mit	Posted: 11 Jul 2025, 02:59 PM
yeah whatever Admin Posts: 629 Joined: 4-May 16	QUOTE (Grumpsimus) I haven't got Mk IV yet, still waiting. However, the one thing that I will really miss is the timezone markers for GMT, BST etc, these are a pretty unique feature for any clock. I hope that they can be reinstated for the Mk V. This is difficult with the automatic timezone. I considered adding a small dot-matrix display but it would be difficult to make this match the brightness/look of the rest of the display. Another thing I've considered is to have the option to replace the last three digits with the timezone abbreviation, but this doesn't work for areas with four-letter abbreviations. Currently, the clock just has a mode (cycled to via the buttons) which reads out the full name of the timezone, rendered somewhat awkwardly on the 7-segment displays. QUOTE (Grumpsimus) This got me thinking about what time is being displayed? It appears to be GPS time. Because there are no leap seconds in GPS time, it is now 18 seconds differeny from UTC. Maybe you could clarify this? The GPS satellites broadcast the leap-second offset with each message, and the GPS module performs the correction for us. The NMEA data conveniently tells us UTC. If we specifically wanted to display GPS time, a custom zone could be added that would just subtract 18 seconds. QUOTE (jonas) Is there a way to make the blink on MKIII regular? I am planning to use it in an art installation. Thanks again! There's a build flag to disable the blinking on the Mk III (see this commit) aside from that you'd need to edit the firmware. -------------
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Grumpsimus	Posted: 12 Jul 2025, 11:25 AM
Member Posts: 4 Joined: 10-July 25	Thanks for confirming that the clock outputs UTC. I wasn't aware that the GPS signal includes the the leap seconds offset. It seems likely that leap seconds may be abandoned, although it wont be for sometime yet, it is due to be discussed in 2035! I can see the problem with the automatic timezone and much as I like the timezone markers, I think another approach would be to display the UTC offsets - as this is the really important information. This could be done on really small 7 segment LEDs. The UTC could be a laser cut out over a rectangular LED as it would always on. -------------
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mit	Posted: 15 Jul 2025, 11:41 AM
yeah whatever Admin Posts: 629 Joined: 4-May 16	The clock has a mode to display the current UTC offset, but again it is accessed through the buttons. Having it permanently visible as extra digits after the time would be ideal but brings in a lot of other problems. If we use smaller digits, it's difficult to match the brightness at all levels (would probably need another nonlinear curve). But the main issue is that it would make the clock much wider, especially if it's to the second. I haven't dismissed the idea of adding another hinge, so a very wide precision clock could fold up like an S-shape, but it might be a bit ridiculous. -------------
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jonas	Posted: 15 Jul 2025, 03:30 PM
Member Posts: 8 Joined: 29-May 25	QUOTE (mit) but it might be a bit ridiculous. I am afraid we like ridiculous around these parts. -------------
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Grumpsimus	Posted: 15 Jul 2025, 09:46 PM
Member Posts: 4 Joined: 10-July 25	I didn't really want to see the clock made any wider, the current one hinge design seems a very good compromise, hence my suggestion of smaller digits. But I can clearly see the problem of making the brightness levels on different LEDs match. Maybe, a slightly different approach would be to have remote to call up different screens? Incidentally, I think the auto timezone feature of the Mk IV is unique for a GPS cloock. I am not aware of any other GPS clock having this. Satellite watches by both Seiko and Citizen have auto timezone setting. However none of the Seiko GPS clocks(mainly sold in Japan) have this, it is all manual setting of the timezone. -------------
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mit	Posted: 16 Jul 2025, 08:03 PM
yeah whatever Admin Posts: 629 Joined: 4-May 16	QUOTE (Grumpsimus) Maybe, a slightly different approach would be to have remote to call up different screens? You can remote control the clock over the USB port, if that helps. But I hadn't considered giving it a wireless remote, it wouldn't be too hard to add a little IR sensor. -------------
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Grumpsimus	Posted: 17 Jul 2025, 02:14 PM
Member Posts: 4 Joined: 10-July 25	I was really thinking of a wireless remote control, which could be useful. The clocks are often mounted on the wall and physical buttons not always easy to access, so a remote would be ideal. -------------
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