Giant 7 segment LCD/LCD Clock

[Valiant]

Hey all,


So I think I want to make a big countdown timer. It needs to count down from 14 years. I want it to be about 100-150cm long. I would like it to be in the style of a 7 segment lcd clock ie https://www.youtube.com/watch?v=HpN9kdgLfgc

I do have loads of addressable 3528 LED tape, so could segment and use that with diffusers. Or I could save that and get some non addressable ones.


How could I do the timer? I would like a battery backup that lasts at least a few days.

[Diver300]

The addressable LED tape should let you do that. You will need some type of processor to be the timer and address the LEDs.

For backup, I would use a GPS receiver. I assume that the end date is fixed, so you can code that in. I also guess that you aren't actually wanting to  get the clock to light in a power cut, so having a GPS means that it will start up in a few seconds after a power cut of any length, without needing setting buttons, or any of the code that you would need to set the time.

[Kim]

Yeah, if you can't get display modules big enough then addressable LED strip sounds like a good way to do it. Microcontroller of choice to control it, and a time source.  Sort of thing Arduinos or Raspberry Pis are good for, depending on what sort of environment you're most comfortable programming in.  NTP might be faster than GPS if you have WiFi available and/or poor GPS reception.  Or just use a realtime clock chip with battery backup, but then you have to provide a way to set the time (unless you have an operating system doing that side of things for you).

[Diver300]

I don't know how fast you need / want the time to right after power cuts. GPS receivers just send out the data strings each second without being asked, so you just have to read the time and date out of that. If you are only wanting time there is no point waiting for a position lock, and the time to wait drops from 30 s to about 5 s. However, if it is in some windowless room, GPS could be a problem.

[rogerzilla]

Hey all,


So I think I want to make a big countdown timer. It needs to count down from 14 years.

This reminds me of the website someone made in the 1990s that did absolutely nothing, except count down the days, hours, minutes and seconds to Britney Spears reaching the legal age of consent*

*I believe she's from Louisiana, so it seems to be 17 unless she marries them first.  And there's probably an exemption for first cousins and the family cow.

[aidan.f]

I would  not rely on a  RiPi to  run unattended for 14  years.  An Arduino would be more reliable and with lower  power requirements easier to keep running (with displays  blanked) during power outages. - Even that would require at least one back-up battery swap-out.

[Kim]

I would  not rely on a  RiPi to  run unattended for 14  years.

This is true.  IME they seem to manage either hours or months before developing spurious IO problems that require a power cycle, for reasons that aren't entirely clear.

An Arduino would be more reliable and easier to keep running (with displays  blanked) during  power outages.

Does it need to keep running?  Surely working out where it should be in the countdown and getting on with it on bootup is sufficient?

[Valiant]

Arduino is what I was thinking. I'll be using LED tape. This is gonna be a big heavy monolithic beast, 2001 style. So I'm just going to pile in a couple of 12v 120ah SLA batteries in there for added heft so I'm not worried about power cuts etc. I just like the idea that it might annoy/freak out someone enough that they might try and unplug it, but then realise it's fooking heavy and it's still counting down. I'm also going to use a light sensor to trigger a sound when its covered over or moved into a big enough cupboard etc lol.

[Kim]

I just like the idea that it might annoy/freak out someone enough that they might try and unplug it, but then realise it's fooking heavy and it's still counting down. I'm also going to use a light sensor to trigger a sound when its covered over or moved into a big enough cupboard etc lol.

That reminds me of the time our drama society scenery was trashed by the Christian Union.  If you're going to make a thing and leave it where it will annoy people, expect it to get vandalised.  (Related lesson: If security tell you the room will be empty until the following evening, with a view to not having to wait for you to pack everything away, don't believe them.)

[Valiant]

Yep I am, its mostly an art project/social project. It's the countdown on the lease of the building.

[aidan.f]

So if it is to be portable, on the timing front, just use a good o' xtal rtc and add/code a couple of buttons to manually add / remove leap seconds every few months. Who's to know if it's a little bit out?

[David Martin]

I have built some similar things before.

Power may be your issue. If you use the neopixels then they can swallow a lot of power. You may be better with a flip board digital clock like railways used to have. Or ePaper.

For control, an arduino and RTC chip are fine - that may be as much as a few seconds out after 14 years. You could do battery backup with a LiPo battery and pass through charger.

A 100 LED neopixel strip will consume up to 18W, I had to use a minimum 2A supply. 

[Kim]

Yes, those LED strips can be power-hungry.  They also benefit from being fed power from both ends if you're running more than a metre or so, but if you're hacking them up into 7-segment figures, then that's less of a problem.

Main gotcha is if you can't mount the power supply close to the LEDs - at high currents the voltage drop on the cable run can be significant, and the LED drivers don't like their power supply dropping out.  The proper way to solve this is with a PSU that has a remote sense input.

Flap displays are lovely, but unless you happen to dumpster-dive a suitable one, expensive.

LED matrix displays are another off-the-shelf option, but they often aren't particularly elegant about how they refresh on receiving external data.  I wouldn't want to do a seconds countdown on one unless I could make the display controller do the updates itself.  Minutes would be fine.

[David Martin]

https://www.ebay.co.uk/sch/i.html?_nkw=flip+disc+display for some reused flip disc which will be about the same or cheaper than building an equivalent with LED strips.