Am 11.10.2015 um 13:20 schrieb Orchid Win7 v1:
> So now I'm wondering about different types of LCD.
> 
> At the bottom end, you have those silver ones they put in calculators.
> Usually a 7-segment one. I have a graphing calculator somewhere with a
> dot matrix LCD, but still silver, with no greyscale capability.
> 
> I'm wondering... Is there a specific *name* for this type of LCD?

"7-segment LCD" maybe?

> What
> does it cost to put one of these into your product? Like, if you're
> buying a couple of thousand of those things, what's the unit price?

You might ask a quote from a company that manufactures those thingies.
Or a distributor. You know, like Farnell:

http://uk.farnell.com/displays-lcd_7-segment

> How much circuitry does it take to drive it?

Zip, as long as you choose a static panel (one single common contact,
plus one contact per segment) as opposed to a multiplexed one, or go for
a complete module. A microcontroller with enough output pins and the
correct output voltage, that's all.

Directly driving a multiplexed panel (segments connected in a
matrix-like fashion) is a much more complex issue (especially so in the
case of non-TFT panels), as you'll need the capability to drive each
line to more than two different voltage levels. Some microcontrollers
provide built-in multiplexed LCD support though, and may only need a
dozen pieces of "bird seed" (resistors and capacitors) to generate and
stabilize a bunch of different voltages.

> At the other end of the scale, you have the stupid-DPI full-colour
> back-lit LCDs with touch sensitivity that they put into every mobile
> phone, ever. What do *those* things cost? I'm guessing you need way,
> *way* more hardware to drive it. (An entire framebuffer, for starters...)

No, not really - you only need more output pins to drive the thing. And
as they're usually TFT, they may actually be easier to drive than
7-segment muxed displays. Depending on your display content you don't
even need a framebuffer: If text is all you want to display, you could
create the actual data on the fly from a text buffer as you refresh the
panel.

> I've heard it said that on "most" electronic devices, the buttons and
> lights are the most expensive part. As in, removing one button or one
> indicator light is a significant cost saving. So a toaster with three
> buttons is "much" more expensive to make than the same toaster with only
> two buttons. I'm not sure why this is; presumably because it's awkward
> to assemble a mechanical switch? (I.e., you have to have an extra step
> where a machine inserts all the moving parts into the right places.)

It's often worse than that: Depending how the switch is mounted, manual
labour may be required.


> I'm just wondering... High-colour LCDs are in even cheap phones now, so
> the LCD itself can't be all that expensive. So why don't more devices
> have these displays? For example, at the gym, the treadmill has a
> 7-segment LED display, and three buttons for cycling through the menues
> and selecting the option you want.

Probably because (1) display quality is /the/ top selling point in the
mobile phones market, even in the low-cost niche, while it is less
relevant in treadmills; (2) in the mobile phone market per-unit margins
are minimal, and profits are made by volume, whereas in the treadmill
business volume is low, and profits are made on a per-unit basis, so
mobile phone manufacturers can get significantly higher discounts on
displays than treadmill manufacturers; and (3) mobile phones have
mind-bogglingly fast development cycles, and adapting an existing
hardware design to use a different display is a routine process; also,
serving a volume market, development teams can be large, possibly even
with a dedicated expert for display technology; in the treadmill
business, development cycles are much longer, adapting the hardware
design to a different display is less pressing and therefore not done
with every cycle, and the development budget may even be too small to
have any dedicated embedded computing hardware expert on the team at all.


> What *will* cost money, of course, is the cost of changing a product
> you're already making. Like, if you already make this thing, and people
> are already buying it, why change it?

Also, what *will* cost money is changing an existing embedded computer
design to drive an entirely different type of display, as opposed to
just adding one more switch or even just changing the software.


> I'm sorry, what was I talking about? Oh, yeah, LCDs. How come (for
> example) my washing machine doesn't have one? I've only ever seen them
> on the most expensive ultra-luxury models. Surely this stuff isn't
> actually that expensive to manufacture anymore?

The question is, would you pay for it?
Would your decision to purchase model X of brand A instead of model Y of
brand B really depend on the presence of an LCD, or would it instead be
driven by a gazillion of other factors? And would you really pay, say,
30 GBP (*) for a multi-color 3.5" 320x240 dot matrix LCD that doesn't
show any more information than the otherwise identical model with just a
rotary knob, a set of switches and a 7-Segment LED display?

(* Wildly guessing here, based on Farnell's offer of the MIDAS
MCT035L6TW320240LML for about 15 GBP apiece at a quantity of 600+, plus
an overhead of 15 GBP for protecting the module against humidity and
vibrations, using a more powerful microprocessor with more I/O pins,
physically connecting the display to the microcontroller, and last not
least developing the modification in the first place.)

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