My preferences are:

• 2.5" - 4" screen diagonal
• 150+ DPI

With pixel throughput you mean the resulting refresh rate right?

This LCD that I used for prototyping: https://wiki.apertus.org/index.php?title=Dictator is really slow in terms of refresh rate but if you update just a small part of the image (eg. one button label/text) the delay is unnoticeable. Since we do not plan to display live images/video I think this is perfectly fine. Of course faster refresh rate is preferred in general.

what about this one?
http://www.amazon.de/SainSmart-3-2-TFT-LCD-Display/dp/B008HWL8QS

more infos here:
http://www.sainsmart.com/sainsmart-3-2-tft-lcd-display-touch-panel-pcb-adapter-sd-slot-for-arduino-2560.html

17€ is pretty cheap

or 480x320 @3,5" https://www.youtube.com/watch?v=5HfSXTHcczw it's similar to the pitft

my preference are:

4" @ 150+DPI slow refresh rate possible

eink?
open source eink! and the projects page

i had this phone (motofon f3) and was pretty happy with readability in sunlight!
and this kindle replacement eink 6" screen is too big but interesting i think
about 40$ 2,7" eink on adafruit, similar product with refresh rate on youtube,
(another youtube link )

Ah that reminds me, another important parameter for the selected LCD is that its readable in direct sunlight.

So it should either have bright enough background illumination or be the kind of reflective LCD that can be read in sunlight even without background illumination.

what about an ink-display? at least power consumption would be very low an it would be readable even in brightest sunlight. on the other side it is not so reactive like an lcd or simulare display type.

@bergspetzl
Did you find any available parts that you would recommend for e-ink displays? I would be quite interested to evaluate this.

Otherwise I guess what we would need is a "transflective LCD": http://en.wikipedia.org/wiki/Transflective_liquid-crystal_display

what about the open source project i have posted?
here @ seedstudio.com

In T200#2963, @christophvarga wrote:

what about the open source project i have posted?
here @ seedstudio.com

Also very interesting, the panel they are using is this: http://www.pervasivedisplays.com/products/27
25$

eInk is very interesting. is it possible to change just the pixels that changed?

it should react in under one second.

a small front light would be nice for use in almost darkness.

A small screen (3-4") should be around 30$. i don't know how "budget" it is for that project, but it really would help save energy. maybe you can also get cheaper ones somewhere (had a look on alibaba). there is even color e-ink on the market. everything except audio levels could be well displayed. another advantage, for assistant or others, would be a stable picture on any view angle.

what about this display, e-ink, Active Area 66.0 x 88.0mm (4.3 inch), refresh time 260ms, 230dpi
or different size, Active Area 45.7x76.16mm

interesting finds!

I already ruled out e-ink already because of the slow refresh rate of the display.

Have there been any technological advancements in that area?

I emailed http://www.eink.com/ if they have a suitable product.

eink might not be too slow if only (small) part of the screen is refreshed. And it would be damn cool to have all the settings shown even is the camera is not powered :-)

so the battery is shown as full even if it's empty? :D

i think eInk is cool because it's readable in sunlight and consumes very less energy. (but do it really make a difference?)
also, what's about backlight?

I know it's pretty late for such an input, but i wonder if we have decided right.
Shouldnt we opt for an transreflective LCD? Something like that one
I searched arround a while for sunlight readable displays and the best which comes up are transreflective-monochrome ones. Just now i held my audio recorder with it's monochrome LCD in my Hand and i am impressed by it's readability.
We made the decision already therefore i totally understand if we stick to it!

I am also concerned about sunlight readability of the current LCD but we are building a first prototype not ordering 1000 units already so I think for the prototype its perfectly fine to just see and test it then, if we see that its completely unreadable in sunlight then its the perfect moment to reconsider the LCD and still keep the rest of the components the same.

For any LCD/LED/eInk display that we want to consider, please first make sure that a datasheet is available and link it here, so that we can do some basic technical plausibility checks ...

Thanks in advance,
Herbert

i got the data sheets for the mentioned lcd

from walter: http://www.sharpmemorylcd.com/aboutmemorylcd.html
(look at the 4.4" sized display (same resolution as our latest lcd)

https://www.adafruit.com/product/1393