picking custom LCD design options

[doanerocks]

Hi Folks.  I am working on designing a clock that you never have to set the time for.  It will get the time from NTP/SNTP or GPS.  I never found a display I really liked so why not design my own display.  I wanted it to be big enough to see from across the room and readable during the day with no backlight and have the possibility to add a backlight for night time viewing.  I have the design I am hoping to use attached.  I need some help is determining what some of the specs should be.  I believe I want 3.3v drive since that is what the esp32 driving it will use.  I do not know how to determine what duty, bias, and frequency I should be using.  I know I don’t want any flicker when possibly filed.  Is flicker even a thing with LCD like it is with LED bulbs?  How do I determine what values I should ask for?  What else am I missing?
Yes I watched all the dave videos about making a LCD from scratch.  I will have to compare the costs of COG and non-COG but I am planning on using pin terminals.

[sokoloff]

If you want across-the-room visibility, I'd consider prioritizing the HH:MM part of the display even more than you already have. (Probably no one needs to read seconds or AM/PM across the room, but at-a-glance HH:MM is a good feature.) On the same sized glass, you could widen the HH:MM and shrink and/or stack the :ss part of the display.

I can't give useful advice on the specific LCD tech beyond what Dave's videos have covered.

[doanerocks]

Thank for the suggestion.  That is worth considering, but I think I will keep the digits the same size for at least the first version. 

[tooki]

If your goal is a clock you can read from across the room, then I think your design priorities are wrong, in that you’ve allocated tons of space to unimportant elements, at the expense of the most important elements of all, the time digits.

Even if you keep the seconds the same size, at least shrink the massive colons and AM/PM indicators. Your digits are very narrow, and spaced a bit close to each other, so the digits are going to be hard to read. Meanwhile the colons, which don’t actually carry any information, are gigantic and widely spaced from the digits, and the large AM/PM indicator (which is of only secondary importance since it’s usually obvious from context which one it is), all take up valuable space.

Furthermore, the way you scaled your digits means the vertical segments are far thinner than the horizontal ones. Again, reducing readability. (And it doesn’t look nice.)

[doanerocks]

I will take the digit layout consideration.  I was not really looking for graphic design assistance but more in terms of duty, bias, frequency, and drive.

[barshatriplee]

You can chose these displays. Can be seen from several feet away.
https://www.sparkfun.com/products/8530

[SeanB]

Standard for these displays is a 32 Hz refresh rate, generally divided down from the clock drive, but not too critical. With that number of segments to drive a COG will be better, as then you will find driving will be handled entirely by the COG device, though you also want a good contrast ratio, probably better than 1000:1, so a COG will at least mean all you need is a bias supply voltage, which will handle display contrast.

Design wise better visibility will be to widen the thickness of the HHMM side, make the AM PM a block above the SS display, and also for the colons to be a rectangular block instead of round, taking up 1/3 of the height of the segments of the main display segments, possibly even with the same end shape. Also for the bottom display easier to make the entire row a graphical display, all dots, giving you a 16 character 1 line display area instead.

[doanerocks]

@barshatriplee I have seen those displays before.  I am not looking to make an arena scoreboard, they did not fit the rest of the authentic I am looking for.

@SeanB do you say to go with COG because of the amount of pins that would be necessary with out it? 
Yes I do want a good contrast ratio, what determines a good contrast ratio?

OK,Ok everyone wants the time digits wider. It is already pretty wide but I will look to see what I can shimmy around to make the digits wider

Putting a Dot Matrix 16x1 as the bottom row, that is an interesting idea.  the original goal was to have year(digit), month(letters), month number(digit), and day of week(letters). Any idea how I would even draw dot matrix in Inkscape? Dot matrix would make it more flexible for any possible unforeseen changes.  Or possibly just do 16 segment starbursts the whole way across the bottom.  I did have spaces to signify separation, but possibly that does not make sense.  Humm big decisions dot matrix or 16 segment starbursts.
Any idea how to determine the proper duty cycle?

[fchk]

I believe I want 3.3v drive since that is what the esp32 driving it will use.  I do not know how to determine what duty, bias, and frequency I should be using.

This a display with a lot of segments. I don't think this will be possible as a static display. A static display has got only one backplane and a pin for each segment. This is the most energy efficient way but only works up to a certain point (maybe 6 digit numeric displays). Static displays can be driven by standard GPIO pins. You must drive LCD glasses with AC, but the waveforms for static glasses are easy to produce.

Your design will be a multiplexed design with maybe 4 backplanes (i.e. duty cycle 1/4). A segment will lit up if a segment line and the corresponding backplane line have opposite voltages. The waveforms on multiplexed displays are not binary, and you MUST use a special LCD driver chip or a microcontroller with a special peripherial built-in. An ESP32 does not have the necessary drivers to interface such glasses directly. All LCD signals must always be DC free. Any DC component on any pin at any time will destroy the LCD glass.

Look here:
http://ww1.microchip.com/downloads/en/devicedoc/39666f.pdf
https://www.microchip.com/en-us/product/PIC18F8493

and
https://www.nxp.com/products/peripherals-and-logic/lcd-drivers/lcd-segment-drivers:MC_38538
https://www.nxp.com/docs/en/data-sheet/PCF8545.pdf


Since you will need a separate driver anyway the glass itself can also be a 5V type, which might give better contrast especially for multiplexed operation. (but ask your factory for that)

[mariush]

You may be interested in something like this :  https://www.digikey.com/en/products/detail/varitronix/VI-611-DP-FH-W/1118598

It has  00 :  00 : 00  and dots between each digit if you feel like using them , and it's 137 mm wide, 45 mm tall. Not quite 200mm, but still quite big digits. Add your own backlight display and you're good to go.

Maybe use 2 of these  or use 2 smaller panels for the secondary stuff (maybe two of those dot matrix style displays, to give you the flexibility of using icons or whatever.


Another suggestion, if you're feeling up to it ... maybe considering an actual TFT panel .. for example this 800 x 480 is $18 : https://www.digikey.com/en/products/detail/orient-display/AFY800480A0-7-0N6NTM/13544649
It has a 24 bit RGB interface, but if you're only gonna do black and white, you can basically tied all 8 reds to one input, all green to another and same for blue ... then all you gotta worry about is having a fast enough processor to pump the bits.

[rdl]

Not only do the digits need to be wider (about 2:1 h:w) the vertical segments need to be thicker. In other words, their width needs to be equal to the horizontal segments height, like your bottom row is.

Also, I think the colon indicators are way too big and have too much space around them. For a clock they could be removed completely and it would still be readable, as long as the digit pairs are well separated, but I wouldn't actually go that far.

[doanerocks]

@fchk sorry when I said " esp32 driving"  I mean I will be using a esp32 as the microprocessor but I sill plan on using a LCD driver. 

[DavidKo]

You do not need AM indicator. If you create smaller seconds, than PM indicator can be above them. The saved space you can use to make wider numbers for HH and MM.

[doanerocks]

@DavidKo are you saying only show PM and assume AM if nothing is shown? 

I am in the process of redoing the 7 segments so that all segments are the same length.  This changes the layout a bit.  I am also working on changing the bottom row into a 16x1 Character.  It is more complicated to design but it should be more flexible in the end.  Changing a

[sparkydog]

I'd agree with everyone that says the time digits are too narrow. However, playing with it a bit myself, I actually feel like 2:1 might be a bit too wide.

If you aren't wedded to 200mm width, I came up with this (see attachment). (I didn't try to redo all of the bottom-right segments. Let me know if you'd like the SVG.)

Personally, I'm not necessarily a fan of the seconds digits being smaller, though it seems to be quite popular. If you made those smaller, you might be able to squeeze a 'PM' above/below them (omitting 'AM'). Or, if you make the 'AM'/'PM' small enough, you might be able to shove them one each above each of the two seconds digits. (I also considered using something that can change between 'AM' and 'PM', but having them in distinct physical positions will make it easier to identify which is indicated at a distance.) Another interesting alternative would be to shove an 'A' and 'P' inside the first of the hours digits, keeping in mind that the only digit that will ever be displayed when AM/PM is relevant is a '1'.

I trust you will support 24 hour time . I hope you will also consider supporting a variety of date formats; at the very least, "WED APR 5 2023" and "2023-04-05 WED".

[doanerocks]

sparkydog@"I trust you will support 24 hour time . I hope you will also consider supporting a variety of date formats; at the very least, "WED APR 5 2023" and "2023-04-05 WED"."
Yes 24 hour time is superior and I don't understand why everyone does not use it even though that is not what I was brought up on. 
What would be nice if I could have the A and P of AM/PM occupy the same space with one on top of the other but I am pretty sure that is not possible. 
I was going to have year, month, day, but like I have said I think I will integrate a 1X16 character display right under the time so it would be possible to have many permutations. 
I am not set on 200mm, I just thought it was a good size.  In order to keep each number segment the same size the numbers are now a bit stubbier.
I hope to have an updated design in the next couple of days to share. 

[rdl]

The difference between A and P is just one segment if you use 7 segment style. If you want to add the "M", just add a second digit and turn it sideways.

[tooki]

If you aren't wedded to 200mm width, I came up with this (see attachment). (I didn't try to redo all of the bottom-right segments. Let me know if you'd like the SVG.)

Having experimented with my own designs for LED filament displays, I’m pretty sure those digits are just too close together. Up close it’s fine, but for OP’s expressed use case of reading from across the room, it’s no good. For example, it can become quite difficult to tell apart 12, 13 and 18.

[sparkydog]

What would be nice if I could have the A and P of AM/PM occupy the same space with one on top of the other but I am pretty sure that is not possible.

As rdl noted, that would be trivial with a pair of 16-segment characters (which you could electrically reduce to two bits). As I previously stated, however, I would personally be against that. I've actually seen many clocks where PM is indicated only by a dot (usually with a tiny, silk-screened label that can be read up close). If the 'AM'/'PM' indication occupies the same space, it has to be legible. If there is a positional component, someone "used to" the clock only needs to be able to tell what position is "on".

I’m pretty sure those digits are just too close together.

Yes, I think you're right; stretching things to 288mm would be better.

[doanerocks]

Here is the updated design.  The rectangles along the bottom are placeholders for Character LCD, in this case a 1X16.  Any idea what the keep out between elements needs to be?
The black bar between the top and the bottom will be removed.  I just put it in to help me design.