EEVblog #1105 - Custom LCD Design - Part 3

[EEVblog]

The $100 low cost custom LCD finally arrives!
Will it work as intended?

[Muttley Snickers]

Interestingly all of the segments on the four digits directly below for the current display appeared rock solid in comparison, the only difference between the two was that you had the CV icon activated the entire time on the voltage display.

[EEVblog]

Interestingly all of the segments on the four digits directly below for the current display appeared rock solid in comparison, the only difference between the two was that you had the CV icon activated the entire time on the voltage display.

Yeah, when you get marginal drive voltage like this on complex multiplex displays, they aren't exactly consistent.

[Bud]

Nice looking display after the voltage mod! Perhaps you could play with backlight to get a feeling how it may look with bbacklight on in the final product.

[SilverSolder]

Looks awesome - very interesting what is possible these days!

What kind of price range would one expect for higher quantities of this kind of thing?

[mk8038]

Mr. Jones

Please note, the LCD bias generator of HOLTEK's device is supplied from a dedicated pin VLCD.
I would suggest to slightly increase this voltage while maintaining VDD at its nominal.
Please observe data sheet block diagram and application circuits

[FrankBuss]

In case someone was confused like me that 6 o'clock is not 180°, this is the description:

http://www.hantronix.com/files/down/v-angle.pdf

It also explains that changing the voltage can improve 6 o'clock viewing for 12 o'clock displays and vice versa, but it reduces quality for the indented viewing direction at bit. I guess it is a good idea to use a digital pot, and allow even the user to change it.

[EEVblog]

Mr. Jones

Please note, the LCD bias generator of HOLTEK's device is supplied from a dedicated pin VLCD.
I would suggest to slightly increase this voltage while maintaining VDD at its nominal.
Please observe data sheet block diagram and application circuits

You can't (or shouldn't) increase  VLCD above VDD.

[radit68i]

name of manufacturer, website?

[ckambiselis]

Dave do you have another test bed, just in case the problem is on the testing kit?

[WN1X]

Dave,

I assume you have tested all of the prototype displays to see if they exhibit the same problem?

[mk8038]

My bad.
There is an appropriate note in data sheet I missed.

[richnormand]

Interestingly all of the segments on the four digits directly below for the current display appeared rock solid in comparison, the only difference between the two was that you had the CV icon activated the entire time on the voltage display.

Yeah, when you get marginal drive voltage like this on complex multiplex displays, they aren't exactly consistent.

I remember seeing a similar issue years ago with nematic custom LCDs.
The issue was variable between panels to non existent on some.
I also remember that it was non-linearly temperature dependent. So the panels behaved differently in a colder room. You might want to look at that.
A partial solution was found by using a different formulation of liquid crystal in the assembly.

It will be nice if the company gives you permission to identify them.

Nice video 

[siealex]

Is it possible to order an exact copy of an old clock LCD? Of course, with given pinout and segment map, but not necessary with exact copying the shape of segments.

[EEVblog]

Is it possible to order an exact copy of an old clock LCD? Of course, with given pinout and segment map, but not necessary with exact copying the shape of segments.

Sure, they will make anything you want.
But if you just want one they will charge you a lot.

[EEVblog]

I assume you have tested all of the prototype displays to see if they exhibit the same problem?

Yes, all basically the same.

[EEVblog]

Dave do you have another test bed, just in case the problem is on the testing kit?

Not yet. But it's very unlikely to be the hardware.
Of course it could be the HT1622 chips drive capability or some such, and it may very well be different with a different LCD controller, but that's beside the point.

[Andrew McNamara]

Not yet. But it's very unlikely to be the hardware.

Given how well that single digit test worked with the common open-circuit... 

[Mr. Scram]

Ever since the last episode I've been wondering whether this is a loss leader for them. Dave weighs in on the matter in the video and considering the not very impressive costs of it all I tend to agree with him. More to the point I've been wondering whether I could buy custom LCDs from someone without lying to them about potential future orders. It'd be awesome to be able to buy LCDs like you can buy PCBs right now. I think they could double the cost and it'd still be interesting, though I have no way to judge whether that would make sense to them.

I think that any company specifically advertising with this ability might enjoy a lot of interest. It'd not be PCB cheap, but I think many people will consider $100 to $250 acceptable for custom LCDs. I don't think anyone is actually doing this at the moment, right?

[boffin]

My question on all of these custom LCDs is why does everyone use such small decimal points?  With big zeros, it's often easy to lose the decimal place.

[Maveltjes]

I took the liberty to improve the display design.. It's a hobby of mine that I picked up recently.
I hope I don't stab the original designer in the back, and as well hope that Dave sees this.

Too late of course, but perhaps I could help with a future project. (I am not very technical, I just like old school LCD's....)
There are several subtle improvements, but the most obvious are the 'Casio style' digits, and the bigger decimal points.
And note the cute battery indicator
It should be completely compatible with the existing design (other than re-drawing all connections etc.)

I can't attach the Illustator *.ai file but could send it when requested.

[boffin]

...
There are several subtle improvements, but the most obvious are the 'Casio style' digits, and the bigger decimal points.

Love the bigger decimal places.

[ivanjh]

You can't (or shouldn't) increase  VLCD above VDD.

I see the datasheet says "The voltage applied to VLCD pin must be lower than VDD." It doesn't say why, or how much lower.
Their own example has a 1V drop: "Adjust VR to fit LCD display, at VDD=5V, VLCD=4V, VR=15k+/-20%."

The LCD common/segment sink test conditions on the D.C. Characteristics all seem to have 0.3/0.5V for VOL (output low) (I'm not sure if that was measured during testing, or to be expected).

Is the HT1622 capable of "full rail-to-rail" output? Does 3.3V VDD & 3.3V VLCD provide +/-3.3V at the LCD? Or is there some drop/head room required between VDD & VLCD?

[bitwelder]

...
There are several subtle improvements, but the most obvious are the 'Casio style' digits, and the bigger decimal points.
...

Reading the 'Casio style' expression made me think: generally speaking, is there any copyright on the LCD outlook, the way there is e.g. for certain typographic fonts?

[Maveltjes]

Reading the 'Casio style' expression made me think: generally speaking, is there any copyright on the LCD outlook, the way there is e.g. for certain typographic fonts?

For using fonts for static items (like AC, min, max in this case) there is no problem as long as you know the font(s) are licensed for any purpose.

The 7 segment LCD was invented very long ago, the very first design was actually an 8 segment.
My segment design here has rounded edges and separation angles similar to many Casio devices, but is not literally a copy. This is a quite common 7 segment design also used by other brands.