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LCD displays

:: EPE Chat Zone ­:: ­Radio Bygones Message Board :: » EPE Forum Archives 2005-2006 » Archive through 19 November, 2005 » LCD displays « Previous Next »

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Camm
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Username: Camm

Post Number: 26
Registered: 09-2005

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Posted on Tuesday, 15 November, 2005 - 06:21 pm:   Edit Post Delete Post Print Post

Hi I wish people designing pic projects in the mag would get away from using intelligent displays. They are far too expensive for the type of person using this magazine. How about using cheaper lcd displays or 7 segment displays, which are up to one tenth the price of 2 line 16 sebments ones. Any comments?
Mac
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Mikehibbett
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Username: Mikehibbett

Post Number: 281
Registered: 04-2005

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Posted on Tuesday, 15 November, 2005 - 06:53 pm:   Edit Post Delete Post Print Post

You can buy 2 x 16 LCD's brand new for less than 8 pounds in the UK, and much less in the States. Low cost microcontrollers are getting so powerful these days that it is possible to build incredibly complex projects with them. Dropping back to a few 7 segment displays as a user interface would require severe 'dumbing down' of such projects. There are decades worth of simpler projects out there in back issues of magazines and on the internet if you wish to build alternative low tech projects.

With regards to cheaper LCD's at 1/10th of the price, could you tell us where? I'd love to use them.

Mike.
-----
www.drivesentinel.co.uk - Home build GPS Speed Camera Detectors
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Microguy
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Username: Microguy

Post Number: 477
Registered: 09-2005

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Posted on Tuesday, 15 November, 2005 - 06:57 pm:   Edit Post Delete Post Print Post

Power is a issue.

Look at COG displays, Chip On Glass, they're a bit cheaper. I like using them because they're cheaper and smaller. Most of the newer displays are mostly framing and circuit board, COG doesn't have that. I bought a couple for $10 each.

And you can back light them too. And they have graphics COG modules.

But if you look at most of the display projects, I think you'll find that they use alphanumeric displays.

So one reason for using "smart displays" is that they're off-loading a lot of the "smarts" onto that display. Allowing the designer to concentrate on the project at hand, and not spending so much time on controlling the display.

In one project, the L/C/F meter a while back, if you used standard LED displays, for one, the cost may end up being more (go price LED dot matrix display's), may need some more interface circuitry, and the code would be at least twice it's current size.

Then there's extra memory. Most PIC's don't have a lot of RAM. With a LED dot matrix, you'll need at least 9 bytes per character. So for a 32 character display (2x16), you'll need at the very least 160 bytes of RAM.

And of course there's processing power. That really shouldn't be that much of an issue though. Or is it??? Most PIC's don't handle interrupts well as I understand it. You can't nest them all the time. So something is gong to have to give.

And then there's the actual electronics layout. With a smart display, I only have say, 16 pins or so to worry about and maybe 5 square inches of empty space.

try putting a 2x16 LED dot matrix in that same display space. Not with individual display's you're not.

So? You want to use "semi smart" LED displays?? I've got some, they use almost 250mA each, for four digits..... How long will a 9V batter stand up to that abuse?? Ok, take out the tiny "brain", and you're talking 200mA.


And then there's cost of the displays....
You said, what? one tenth?? ok, for 7 segment displays, I'll give you that one. How about Dot matrix?? Let's go back to that 2x16 display??

Let's see, the cheapest 5x7 dot matrix I see is $3.18 (up to $21.73 per digit). So we're looking at $101.76 for JUST the display!

Now, since that's 2x16, or 14 lines by 80 lines, multiplexed.... well, you get the idea, let's add a few extra bucks for the support circuitry like drivers, say $20??

Cheaper indeed...




Now, don't forget, you can take any project that uses a smart LCD and make it use dumb LED's. That's the good part about these projects, nothing is set in stone, you can modify them at will.

You want to use LED's, by all means, please do so. Just as I choose to use COG for some projects, you can choose to use LED's.
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Microguy
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Username: Microguy

Post Number: 478
Registered: 09-2005

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Posted on Tuesday, 15 November, 2005 - 07:01 pm:   Edit Post Delete Post Print Post

Oh yeah, here's an idea for you.

Build your own "smart display". Use a simple PIC, and what ever support circutry you need, and add your display of choice.

Then every time a project calls for a "smart display", just plug your own in there!

I used the Intel 8279 display controler for many projetcs. And almost did the same thing, include the 8279, a few support chips and what ever display I wanted. (don't know if you can even find it now, I've got a supply of them though)

Then I'd have a "standard" display module that I could drop in.

You can do the same thing. And give it what ever software functions you want.
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Terrym
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Username: Terrym

Post Number: 88
Registered: 05-2005

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Posted on Wednesday, 16 November, 2005 - 01:21 am:   Edit Post Delete Post Print Post

Check old printers, photocopiers and telephones, a lot of them use compatible LCD displays.In fact, some later photocopiers with graphics displays are now turning up on the junk pile.
If you only need one for yourself, you can usually get old discarded stuff like this for free.
TM
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Microguy
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Username: Microguy

Post Number: 488
Registered: 09-2005

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Posted on Wednesday, 16 November, 2005 - 01:40 am:   Edit Post Delete Post Print Post

Oh, Good point! Like my "Toy Store" thread.

I'm always up for digging stuff out of the "trash". Sometimes it can be kind of hard to get data on it though. Don't they ever throw away "standard" stuff????

But you can get some really good finds out there, especially graphics displays.

This is also a good point for "toy stores" too.

I bought an brand new "Mail Station" from some store that was closing up shop, K-Mart I think it was, for $10!!

Out of that, I got a really nice case, super typewriter style keyboard and a display that looks like it's 256x128.

Plus the components inside of it, modem, CPU, memory, few discreets and not a whole lot else.

For $10. I wish I had bought several.

I've still got friends working in places, and they give me their "trash". Just picked up a brand new 100 watt switching PS. Now that's my kind of trash!!
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Terrym
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Username: Terrym

Post Number: 89
Registered: 05-2005

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Posted on Wednesday, 16 November, 2005 - 09:23 am:   Edit Post Delete Post Print Post

I've got friends like that, only trouble is, I'm running out of room to store the stuff and time to dismantle it. Although just got a couple of reasonable computers which have been refurbished. Saves having to pay for it .
TM
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Microguy
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Username: Microguy

Post Number: 490
Registered: 09-2005

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Posted on Wednesday, 16 November, 2005 - 05:01 pm:   Edit Post Delete Post Print Post

When I was in IT, *I* was one of those friends!

That's one reason I've got so many laptops now. It also helps when the company is bent on throwing out good stuff too!

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