Flip Display Clock Project

[Mysion]

I wanted a fun project to try and complete before school starts back up in the fall. Thankfully I have a few old flip displays on the "from ebay" pile of electronics. And what a pile it is.

If I can I want to build a slick wood case for it. I do have limited wood working skills and a CNC to call on. I thought I'd document it all here and get feed back on some parts. I've mostly finished the electornics design portion of the clock.

Obviously I need a driver for the flip display. I'll just use a few discrete transistors for that. If I can I want to have a sun rise alarm feature. This means lighting up the room to simulate sun rise. I figure a few LED's will work.

Enough rambling  here's the star of the build a 7 segment flip display.

9$ a pop on ebay. I got five of them. My major regret is that I did not get more.


Here's the current schematic. There's an RTC for obvious reasons(2% ppm) and a I2C GPIO exapnder since I ran out of pins. I'm using an ATMega 48A with every single pin in use (except two analog pins)



This is the real star of the show, the driving circuits for the display. The section on the bottom supply's 12v and selects the segment. The upper portion allows you to select the direction and the segment to flip. This was more complex than I first expected. It might be difficult to fit this on the board... Oh well shouldn't be too bad. That many discrete transistors on will make it look interesting.


Next I need to start working on the PCB design and thinking about the physical construction. I'd rather not have a hot glue based clock so I need to give that some real thought.

So what do you guys think so far?

[tooki]

Looks cool! Comment to subscribe, since I'm working on a clock project myself.

Is that the DS3231 RTC?

[Mysion]

Yep DS3231 is the chip! I love that RTC. Expensive as all heck but no more than a minute deviation a year. No fussing around with IOT and time servers needed. 

What clock project are you working on?

[Gyro]

You Might want to check out Marco Reps's electromagnetic clock project.



Check out the minimum segment switching demo at about 1:30 

[Benta]

Way cool!
I remember having one of those displays in my hand many years ago, and wondering at how light the individual segments are and how smooth the action is.

The only step up would be using those "rolodex-like" digits they still have for the big departure displays at Frankfurt/Main airport (Germany):


A bit worn, and something in the synchronization is failing, though.

[128er]

Followed!

And here is my flip clock. Driver PCB is still prototype. The biggest challenge in this project are my horrific coding skills ^^

[NivagSwerdna]

OOOOO those displays are lovely... if you see a similar set on ebay please post the link.

[tooki]

Yep DS3231 is the chip! I love that RTC. Expensive as all heck but no more than a minute deviation a year. No fussing around with IOT and time servers needed. 

What clock project are you working on?

Like $2? I don't consider that too bad. Certainly worth the added cost over the crappy 1302/1307 RTCs!

The project is fundamentally a giant-digit alarm clock, something I can see without putting on my eyeglasses. With my eyesight, that means digits at least 3"/10cm tall for a clock at arm's length.

Of course, large digit clocks exist for sale, but other than big digits, they tend to be shit (bad user interfaces, etc). So I wanna make one that's beautifully designed in every other way, too! Of course, the building is the main aspect, and it's a good way to put my spotty knowledge to the test -- it's been a great learning experience. (Some of the things I've needed to learn are: driving displays of various types, I2C and SPI, RTCs, buttons and matrices, and various aspects of coding*.)

I'm still not sure what kind of display I'm gonna use. I've been tinkering with a 64x32 RGB panel, but an Arduino struggles to drive it (it is 6,144 LEDs, after all!), and can't do high bit depths, the MCU just isn't fast enough. Another option is gigantic 7-segment LED displays (I finally found a source for white ones, all the way to 5"/12cm tall!). Making 7-segment displays out of WS8212B LED strips is another, which would allow full RGB without too much CPU load. I've even considered making 7-segments from LED filaments, though this is far harder to drive, since they're designed for 60+ volts. (The only firm requirement, aside from size, is that it not be a red LED display. I have an irrational hate of red LED displays.)

Obviously, a display that big, which is bright enough to be visible by day, would be insanely bright at night, so I'm gonna have to use ambient light sensing to adjust it for room light.

Recreating vintage display technology is of course also interesting. Aside from making mock-Panaplex displays with the LED filaments, two other fun approaches would be side-lit laser-etched plastic sheets with the segments, or projection displays.

Other pending items include: generating a pleasant alarm sound, maybe using a GPS or DCF receiver module to receive accurate time signals, perhaps a proximity sensor to wake up the display from dimmed by waving a hand nearby, and perhaps in the future interfacing with lighting projects.

* I'm a terrible programmer, and the coding has been the biggest challenge -- still pending are elegant button handling, and date operations. Real OSes have calendar libraries (with math functions, like adding/subtracting months/days/hours/mins) that handle things like leap years automatically, but I haven't found anything like that for Arduino, and I know that date handling is one of those "Here Be Dragons" minefields full of edge cases...

[NivagSwerdna]

Try RTCLib

[tooki]

Try RTCLib

I've seen it before. It's helpful, but still far too rudimentary (and poorly documented!).

For example, take the task of setting a calendar by incrementing/decrementing a month. It's easy if you're mid-month:

2017-08-04 + 1 month = 2017-09-04 - OK
2017-08-04 - 1 month = 2017-07-04 - OK

But what if you're at the end of the month? What do you do with a remainder?
2017-06-30 + 1 month = 2017-07-30 - OK
2017-06-30 - 1 month = 2017-05-30 - OK
2017-07-31 - 1 month = 2017-06-30 - not simple (naive calculation would produce July 1)
2017-05-31 + 1 month = 2017-06-30 - not simple (naive calculation could produce July 1)

Additionally, from a UI perspective, even if you've handled the cases above, you want there to be "memory" as you increment/decrement. For example, suppose you're decrementing by month from July 31. You want it to remember day "31", even as you click through months with fewer days:
July 31 -> June 30 -> May 31 -> April 30 -> Mar 31 -> Feb 28 -> Jan 31 -> Dec 31 (y-1) -- good
July 31 -> June 30 -> May 30 -> April 30 -> Mar 30 -> Feb 28 -> Jan 28 -> Dec 28 (y-1) -- bad

(This is analogous to how the cursor on a computer remembers where it was on a line as you use arrow keys to move up and down, even passing through lines that are much shorter, but returning to the original horizontal position when possible, until reset by acting on the horizontal position by editing text or using the left/right arrow keys.)

Months are really the problem child of date calculations, since they're of variable length, so you can't simply add/subtract a fixed number of seconds from UNIX time.

[Mysion]

Gyro

I will have to take a look at that. Looks nicely documented. Very well done video.
I like the look he has with the flipping order. I concern I have with that is I have observed that some segments like to flip to a certain position if shook slightly.
Maybe it'll be different when I drive is magnetically.


Benta

I love those displays too! Maybe the next version. 
I've been to a train station in New York with those and the sound is very pleasing if loud.


128er

Looking good! Do yours have a center tap? I've seen the same ones you've got on ebay and no center tap would make driving much more difficult. You've got 4 clocks worth ya lucky bastard! 


NivagSwerdna

Sure here's a link to a similar set  http://www.ebay.com/itm/7-segment-1-Ferranti-Packard-electromechanical-display/160945344354?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649


Tooki

I think we are talking about different variants that fall under the same name. I'm talking about this chip https://www.digikey.com/product-detail/en/maxim-integrated/DS3231S-T-R/DS3231S-T-RDKR-ND/4895475
It's only off by a minute a year at worst. There might be similar chips out there for less but it may be too late to change at this point.... 

I know what you mean by crappy clocks! Good ones cost too much and I'm a cheap bastard!  Large digits are a challenge. I did see some large flip ones on ebay but at 80$ a pop... At sizes that big you could make your own segments out of a diffuser if you wanted. Large IN-18 nixes might work too.

As far as accurate time goes I'm using a chip that's off by a minute a year at WORST. 8$ a chip but simpler than GPS. The last thing I want is another clock that has to be adjusted multiple times a year. I have a enough of those. It has one job and it has to do it well!

As far as calender's go an RTC chip handles it all automatically. Atmel has a app note on implementing a calendar. I can find it if you want. Good luck! Maybe I'll give you some good ideas.

[tooki]

I think we are talking about different variants that fall under the same name. I'm talking about this chip https://www.digikey.com/product-detail/en/maxim-integrated/DS3231S-T-R/DS3231S-T-RDKR-ND/4895475
It's only off by a minute a year at worst. There might be similar chips out there for less but it may be too late to change at this point.... 

I think you misunderstand; I was saying that I don't think $2 for a DS3231 is unreasonable. I was saying that it's worth paying extra for a DS3231, because the cheaper DS1307 and DS1302 RTCs can be very inaccurate. I'm well familiar with the DS3231, since it's what I am using in my project, too.

I know what you mean by crappy clocks! Good ones cost too much and I'm a cheap bastard!  Large digits are a challenge. I did see some large flip ones on ebay but at 80$ a pop... At sizes that big you could make your own segments out of a diffuser if you wanted. Large IN-18 nixes might work too.

Though they're sexy as hell, the digits on the IN-18 are only 40mm (1.8") tall, nowhere near big enough for my purposes.

As far as accurate time goes I'm using a chip that's off by a minute a year at WORST. 8$ a chip but simpler than GPS. The last thing I want is another clock that has to be adjusted multiple times a year. I have a enough of those. It has one job and it has to do it well!

Yep, the DS3231 is very accurate. $8?!? They're a dollar on eBay, premounted on a little breakout board.

As far as calender's go an RTC chip handles it all automatically. Atmel has a app note on implementing a calendar. I can find it if you want. Good luck! Maybe I'll give you some good ideas.

RTCs handle timekeeping (including dates) automatically. But they don't handle anything else. Since they don't have commands to increment/decrement (they only let you write the time/date to the registers, not perform operations on them), then you need to do those yourself, as I illustrated above. And that means implementing all the logic to produce valid dates to push into the RTC.

[128er]

128er
Looking good! Do yours have a center tap? I've seen the same ones you've got on ebay and no center tap would make driving much more difficult. You've got 4 clocks worth ya lucky bastard! 

No, no center tap on the coils. Each segment coil is individual. If you mean that. <- Edited my brain fart

I have enough 7 segment displays to build ten clocks. I bought three complete displays from gas pumps and desoldered all the individual 7 segment displays. I drive them in a matrix with NXP MC33880 driver.

[Mysion]

Tooki

I have a few of the ebay versions but I'm skeptical if they are real or not.  Mouser has a similar price to digikey. The chip is very slick in the accuracy department but you would be hard pressed to determine if one is a counterfeit.  I'm only making one clock so I really do no want to risk a fake chip that's just a normal RTC at heart. Heck whats 7 more $ after spending 80$ for the PCB and buying good wood. I'll do it for the piece of mind.

RTC handling on the micro's side isn't too bad. 99% of the time you won't hit the edge case of changing the day right before leap year. Depends on if your building for your self or production. It can be weird though.

Take a look at page 7 of this app note. http://www.atmel.com/images/atmel-1259-real-time-clock-rtc-using-the-asynchronous-timer_ap-note_avr134.pdf


There's a really nice flow chart there that shows all the things to check for.


128er

Nice number of displays! If you play your cards right you'll have wedding gifts for decades!

[Mysion]

The PCB was fun to work on. The limiting factor was the size of all the switches and buttons on the back. I only have 6 inches to work with and it came out to about 5.4 inches. They also take up most of the space on the PCB. Fitting the driver circuit in was tight. Not as tight as my BCD decoder but it was "interesting" 



On the lower left you have the 12v module to generate the power to drive the displays. On the lower right you have the coin cell and the RTC. The RTC is under the coin cell. With such a large ground plane it's the perfect location. In the lower middle you have the driver circuitry happily taking up both sides of the board.

The buttons take up the top portion. I could have used SMD buttons but I trust though hole more for that. The end total is 8.6 square inches and 321 connections.

Here's the board in glorious 3D



I think I'll use OSH parks fast service. It's pricey but i REALLY want this done before school starts. I think this is one of my largest PCB's to date. Let's hope I don't need a version 1.1

[tooki]

Tooki

I have a few of the ebay versions but I'm skeptical if they are real or not.  Mouser has a similar price to digikey. The chip is very slick in the accuracy department but you would be hard pressed to determine if one is a counterfeit.  I'm only making one clock so I really do no want to risk a fake chip that's just a normal RTC at heart. Heck whats 7 more $ after spending 80$ for the PCB and buying good wood. I'll do it for the piece of mind.

RTC handling on the micro's side isn't too bad. 99% of the time you won't hit the edge case of changing the day right before leap year. Depends on if your building for your self or production. It can be weird though.

Take a look at page 7 of this app note. http://www.atmel.com/images/atmel-1259-real-time-clock-rtc-using-the-asynchronous-timer_ap-note_avr134.pdf


There's a really nice flow chart there that shows all the things to check for.

Well, you coudn't really pass off a lesser RTC as the DS3231, since they use external crystals, while the DS3231 uses an internal temperature-controlled oscillator. The DS1307, for example, is neither code- nor pin-compatible, being just an 8-pin device that does less.

That flowchart is useful indeed, thank you for that!

As for doing it right: one of the things that annoys me most about most clocks for sale is how bad the user interfaces are. So that's definitely not somewhere I'm gonna skimp just because it's a project for myself. On the contrary, it's precisely because I value good user interfaces that I want it to work well, not just OK, never mind something silly like needing to be connected to a computer to set the time (like many DIY clocks I've seen do).

Regarding your PCB: where are the displays mounted?

[Mysion]

I'm still skeptical  after the whole fake FTDI chip thing. They could easily stick a simple crystal in or run it with a micro like the ftdi chips. You would never know it's not a TCXO until it's too late. Maybe I'm being slightly paranoid. 


I think you'll be slightly disaponted with my user interface then lol. I'm just sticking to 4 buttons to set the alarm time and clock time. Then a switch to turn the alarm on and a switch for the sunrise alarm feature.

You could make a really good one with a small LCD and a miniature joystick. My current monitor uses a small joy stick and it makes a world of difference.

My displays will be mounted on a separate frame with 19 wires plugging into a header on the PCB. I'll be quite a job connecting all of them but better that then pay for such a huge PCB!

[Mysion]

This is the 3D model for the subframe or frame that will hold the displays. I went though a few iterations of it making minor adjustments. There will be a few more changes done to it yet. The far right 5th display will be used for AM/PM and alarm indicators. You can see the gaps for wires at the bottom The bottom gap will also be used to make space for the PCB. Thankfully my displays have mounting brackets and I can wire them free hand. The center post will hold what ever I decide to use for the colon.




This is the tentative face plate. I have a design in mind that I need to refine. I'm thinking of going for a modern art-deco look. Some thing that has presence but isn't too flashy. The cut outs on the right are for AM/PM and alarm. I've gone though a few versions of these. I'll print out the newest ones tonight and show a few pictures tomorrow. With no data sheet it took a while to figure the right mounting spacing.

[Mysion]

As promised I printed out the parts so far and here they are!



The indicator window on the right doesn't quite line up but it's an easy fix. One thing I did notice was the printer was printing about 10 thou over. Not a huge issue but I have to be mindful. In the final design only the  sub frame will be 3D printed. The outer parts will be wood.


The design for the clock took me a while of just staring at the displays in the sub frame. Eventually I came up with one I liked. After fiddling around with CAD for a while hear it is!



Sorta of a modern art-deco look I think. I put a ruler at the bottom for scale. It's not massive but it's a good size. 8.5 inches wide. 4.5 inches tall and 3 in deep. I need to work on the hole in the back for the buttons next and try to find a really long 1/16 end mill.


PCB should come in this week so I have that to look forward to!

[Benta]

Nice!
I'd angle the hrs : mins separator as well, but that's just my taste.

[Mysion]

Thanks! That's not a bad point about the sperator. I modified it with an angle and here's the angled version



I like the consistency but I'm not so sure if I like how it's not evenly in the center any more. I'll have to think that one over.

[joshtyler]

OOOOO those displays are lovely... if you see a similar set on ebay please post the link.

There are these. The seller apparently has 10,000. I must say that I am tempted!

[SL4P]

I got away with three buttons for the UI.
Any button/function- timeout after 10 secs = return to clock mode.
BTN 1: Select mode - step across individual digits, then through various functions
BTN 2: increment (digit or displayed value)
BTN 3: decrement (digit or displayed value)

If the clock uses muxed LEDs etc, when not in 'digit set' mode - the inc/dec buttons adjust the brightness.

[tooki]

I got away with three buttons for the UI.
Any button/function- timeout after 10 secs = return to clock mode.
BTN 1: Select mode - step across individual digits, then through various functions
BTN 2: increment (digit or displayed value)
BTN 3: decrement (digit or displayed value)

If the clock uses muxed LEDs etc, when not in 'digit set' mode - the inc/dec buttons adjust the brightness.

Already massively better than all the Chinese clocks/kits that use two buttons.

With regards to alarm clocks, this is where (to the best of my knowledge), Sony got it right ages ago, and nobody else has copied: most Sony alarm clocks are designed such that verifying the wake time also turns that alarm on, completely eliminating the common problem of the user checking what time the alarm is set to, but forgetting to actually turn it on!! Sony alarm clocks with a single display do this by using a button for the alarm, which you hold to set the wake time, and that automatically turns on the alarm (a separate, much smaller button turns it off). In other models, they have a separate display for each wake time, with separate up/down buttons for each alarm, and a button that turns the alarm on and off -- and when the alarm is off, its display is also turned off, so again, checking the wake time necessarily requires turning it on!

It is the latter paradigm that I was planning to copy, probably using a little OLED display for the wake times.

[Mysion]

My biggest gripe with the damned cheap clocks is the ones with an Up botton but no down. To go from 36-34 you have to push it 58 god dam times. 
I might go full office space on it once I have a replacement.

Interesting idea from the Sony clocks. Might have to try it depending on how well mine works out. I figure it'll be one of those things were I'll constantly be tweaking it.

I'll be going for some thing similar to what you have SL4P just with 4.

I do have a small update. I picked out the wood at the local wood shop.

This is the wood I plan to use. It's sapele and ash. I think these two will complement each other nicely.



Here's a bonus pic of the very messy CNC. I need to do a bit of cleaning....