On 13/10/2015 08:27 AM, scott wrote:
>> What about the blue/purple ones? You know, like they had on ancient
>> laptop screens?
>
> Passive matrix too. The key difference is there is no electronics
> per-pixel to hold the voltage over the length of the frame, so the LC
> response time must be very slow (much longer than 1 frame) to keep any
> decent contrast. On an active matrix display the pixel electronics
> (transistor + capacitor) can keep the voltage at whatever you last set
> it to for the duration of a frame, so an LC material with very fast
> response can be used (eg 1 or 2 ms is common now in monitors).

OK. So what's the difference between the silver ones and the purple ones?

>> Wow. I didn't expect it to be quite *that* cheap. Even a simple resistor
>> costs more than that! (Or maybe it doesn't if you buy a thousand of
>> them, IDK.)
>
> If you want 1000 or more you don't buy them from maplin, RS or Farnell.

[Rant] I remember when Maplin used to sell electronics. Now they're just 
a white-box shifting company. You used to be able to go in and just 
*buy* a string of 30 resistors or something. Now they're all like "oh, 
you want 10? Ooo, we'll have to order those in specially. We only have 4 
in stock." WTF?

> Try this:
>
>
http://www.aliexpress.com/item/High-quality-character-LCD-7-segment-LCD-module-3-3V-TN-positive-reflective/32293200442.html

That's... a dollar per display? Damn, you can't get too much cheaper 
than that. I wonder what a Z80 costs these days...


> cost must be significantly cheaper:

Well, I guess that's true enough!

>>> Price is roughly proportional to screen area (the factory doesn't care
>>> much how many screens it gets out of each "mother sheet").
>>
>> Linearly proportional? Or is it "more expensive" to buy really big
>> screens?
>
> Roughly linear - the factory costs to run are mostly independent of how
> small they chop up the glass at the end.
>
> The only complicating factor is yield.

Yeah, I thought that might be the case.

>> OK. Again, that's not nearly as much as I thought. Makes me wonder why

>> makes it a high-colour touch-screen device...
>


>
> http://www.gearbest.com/lcd-led-display-module/pp_231779.html

Damn, that's not bad at all! I'm surprised nobody seems to be using these...

>> I imagine touch would be really expensive - but IDK...
>
> The expensive bit in capacitive touch is the controller IC that does all
> the processing. There is also a premium on this because of the IP that
> has gone into the algorithms etc. The physical bit is very cheap, it's
> just another sheet of glass with some quite chunky conductive layers.

Interesting. I thought all the extra faff of assembling it was the 
expensive part.

>> I don't know, but I'm guessing it must be reasonably expensive to

>> something?)
>
> A good rule of thumb for medium-volume consumer goods like that is that
> the cost to manufacture is roughly 25%-33% of what you pay. The rest is
> VAT, shipping/logistics, paying for everyone who works in all the
> companies involved, and maybe a little bit of profit for each company
> along the way.

Interesting. And here I was thinking the metal is expensive. ;-)

>> Sure, but you don't *make* the switch yourself, surely? You buy an
>> off-the-shelf microswitch,
>
> Someone else needs to make it though, my point was for their size/weight
> switches are much more expensive than a sheet of bent metal because the
> assembly costs are higher (whoever does it).

Well, I guess.

Now you're typical calculator has one of those rubber keypads. I have 
personally assembled those; it's a sheet of rubber, and there's some 
wiggly traces under it. Presumably that's cheaper than a microswitch? 
(Especially given a calculator has, like, *a dozen* buttons...)

> You might be interested in something like this, it gives a detailed
> breakdown of the costs of the parts in the latest iPhone (if you didn't
> know this is a very high-end phone that is expected to sell in high
> volumes):
>
> http://www.techinsights.com/teardown.com/apple-iphone-6/
>


This is interesting on several levels.



2. I didn't know this kind of disassembly was legal. I thought Apple 
would try to sue you for distributing trade-secret information.

3. As expected, the display is the most expensive bit. (Then again, 
isn't the iPhone kind of renound for having a particularly high-quality 
screen?)

4. The next most expensive bit is the CPU, like you'd expect. The RAM 
looks surprisingly cheap tho. (No idea how big it is, mind you!) I 
wonder what kind of CPU... it... er... oh right, it's a custom ARM SoC.

5. I expected the battery to be way, way more expensive than that. 
(Considering that battery life is extremely critical to product success, 
you'd expect the best performance part that can possible fit in the space.)

6. I have no idea WTF "BB+XCR" is.

7. I enjoy that "Other" is nearly as expensive as the CPU.

8. Qualcomm manufactured my lawn mower. They make silicon too? WTF?

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