I would like to display some simple data - eg temperature, number of minutes to the next bus - on a display which can be read from across the room. The display will be wall-hung or sit on a desk or ledge. It should be battery powered, lasting for many months. The data will be collected wirelessly.
I know there are commercial devices like this - eg the Oregon Scientific weather station base units - which run for a year on batteries. But I've not found a customisable solution.
It seems there are two options:
(a) build an arduino-powered display unit. Options discussed elsewhere here include LCD matrix display (good, but most I've found are not readable across a room), LCD large 7-segment (not flexible enough), or maybe even epaper (as the data will only change occasionally, so I could hibernate the processor for 95% of the time).
(b) buy a ready-made display unit and squirt it data wirelessly from a mains-powered Arduino in the next room. This might be a smart-looking option eg tabletop box with nice stand. Or even hack an electronic picture frame. However I've not found anything suitable yet.
I believe you will have to rethink the battery powered idea, I'm afraid. No lcd display is going to be large enough to read accross the room, unless you get an lcd tv, which you can use as an adruino display using the tvout library. But of course an lcd tv is not going to run on batteries.
An led matrix sign could be read accross the room, but again, even a small one won't run for more than a few hours on batteries.
I've never seen large epaper displays available at reasonable cost, or seen anything except tiny ones used with Arduino. Lack of memory may be the reason.
So if I were you I would start thinking about a power supply for your display. I think I might go for 32x16 single colour led matrix driven by Arduino.
Alternatively a small/slim lcd monitor or tv, driven by a Raspberry Pi.
PaulRB:
I believe you will have to rethink the battery powered idea, I'm afraid. No lcd display is going to be large enough to read accross the room
Thanks for responding.
It's not a big room ... and I can read the big numbers on my Oregon Scientific weather unit easily. It has a 6x8cm LCD display and the numbers are 3cm high. Ah ... on closer inspection I see that the big numbers may be a 7-segment display. So perhaps how they do this in commercial devices: a bespoke panel with little and big numbers and symbols is lower power than running a matrix display?
Well, perhaps you could consider a 128x64 graphic lcd. They are large enough to display digits 3cm high, if you use a large font. However, all the ones I have ever seen up to now have power-hungry led backlights. The backlights can be switched off but then the display is almost impossible to read. However, it seems a model of these displays is available that shows black pixels against a plain background and can be viewed without the backlight:
Its a 3.3V device, which means if combined with a 3.3V Arduino, like a Pro Micro, longer battery life looks more like a possibility. Power saving libraries are available which can help reduce the Arduino's power use greatly. If the device contains only an rf receiver and no transmitter, that would help too. You could ask a question on the Adafruit site about what the current use of the display is, assuming back light is off and updates are infrequent. The data sheet says it is 1.0mA max, but I'm not sure if I believe that (the data sheet also says that the maximum backlight current is 500mA, so there are clearly some errors in it!).
