Small screens for portable devices
Graham Stabler
Posts: 2,507
The little 2.5" screen sold by parallax and others is really nifty but it seems a bit inefficient, does anyone know any other screens pf a smal size that might be suitable for inclusion into battery powered equipment without requiring alot of development work?
Graham
Graham
Comments
Had a similar thought Graham.
http://www.xenarc.com/product/index-monitor.html
Just google 7" LCDs, these seem to be the smallest size for car use.
Mass market consumer product so they should not be too hard to get.
Gavin
http://groups.yahoo.com/group/MicroCNC/
I don't want a bigger screen than 2.5" just one that runs a cooler and uses less juice.
Graham
Regards.
Alberto.
There are the cellular phone displays [noparse][[/noparse]available at Spark fun] but the interface is a bit more demanding [noparse][[/noparse]You may have to write an object for it];
The little 2.5" from Parallax;
PDA screens of various sorts [noparse][[/noparse]Try the Palm Tungsten replacement parts via Google];
and
A larger 9-10" TV screen that I've seen in the electronic shops in Taiwan with a tuner box.
If you can use the cellular phone displays or PDA screens, you will have the best power option.
I don't think the 2.5" requires a lead acid battery, though I was the one to recommend such in the beginning.· It appears that it will run on much less current that the 1amp power supply that was recommended.
What I would like to see is a 10" flat screen computer monitor.
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"If you want more fiber, eat the package.· Not enough?· Eat the manual."········
Post Edited (Kramer) : 12/12/2006 5:47:22 PM GMT
Kramer, judging by the head a lead acid might be a good idea for any longevity.
Graham
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Paul Baker
Propeller Applications Engineer
Parallax, Inc.
There is a 5v regulator on the audio board but I don't think it is disipating much power. The board on the back of the LCD has 12v marked on it, this might again be regulated for logic but there is also an inverter circuit to create the LED drive at 20v and that will be more efficient with 12v than 5.
The LEDs are definately where all the power is going as you can probably see in my picture, it really is a bit painfull to look at and the pcb gets hot to the touch. I wonder if they have simply made the screen too bright. It should be noted that the brightness control just changes the LCD contrast and does not change the back light. I wonder if either a current limiting resistor or a different backlight scheme would help to reduce consumption. I'm going to investigate the led driver to see how clever it is or isn't.
Another cool thing is that the leds are side firing into a special sheet which presumably distributes the light around evenly, nice!
Graham
Rsc is a short so I guess that means it is trying to kick out the max current it can for the given efficiency. It might be worth cutting the track and adding a low value resistor.
Another interesting fact, the LCD is marked as Sony!
Graham
Transflective type would be best compromise.
Indoor or outdoor use Graham?
Transmissive are Smile outside, reflective are best.
I am watching the OLED display market carefully these days.
128x128 colour ones 1.2"
Still waiting for a bigger one.
For really low power I am hanging out for the Eink type.
Gavin
My 2.5" runs quite hot. I have my whole demoboard (with screen) hooked up to a 1/2A 12V unregulated Wall wart. My wall wart gets warm. My screen gets quite warm in the front, but stays cool in the rear, supporting the suggestion that the LED's are the source of heat. If you figure out a neat way to modify this thing, I'd like to do the same to mine. I certainly don't need that much brightness while sitting at my desk...
There were discussions over the summer about this same LCD. People were able to reliably run it at 7.5V. I had, at one point, a 9V regulator on my incoming supply (but it ended up giving me issues, so I removed it), and the LCD seemed to run a bit cooler (I'm working from a very poor memory on that last point).
I, too, would like to see other LCD optins, since this one is kinda big for it's actual screen size, IMHO.
-Parsko
After loosing the audio board and reducing the backlight power this thing should be pretty compact. I'm considering packing it along with a propstickUSB, Vincalum Vdrive1, keyboard and mouse connectors and a DB25 for IO into a hand held case with 9v battery compartment (as well as 12v in jack). That would be a pretty cool little widget for development.
Graham
OK so with some better light I was able to determine that the LEDs are actually driven directly from a 20v regulator after the switching one (who knows why).
Current to LCD module board:
without LEDs on: 110mA
With LEDs on: 200mA
Ouch!
The addition of an 80ohm resistor in line with the leds has dropped it to 130mA leaving cool LEDs and perfectly good brightness from what I can see.
There is a 5v regulator on the board also and that runs hot, I'll try running that from the props supply as it should not need much juice.
All that is left to do now is to sort out some voltages for the brightness/contrast and colour to the board and I can ditch the audio board alltogether. I tried just disconnecting the brightness but it then didn't have any so it will need a preset pot or just a potential divider to supply the relevant control voltage.
Graham
The 5v is now supplied from the propeller's regulator and I have cut the colour/brightness part of the audio PCB away to provide easy adjustment of those controls (once only). You can see the current limiting resistor hanging off at the bottom, I may even try larger values once I see how it goes.
After 10min constant running the screen is not noticably warm which is a big change from before.
It may in the end prove better to change the 7805 regulator on the board to a low drop out type rather than run it all off the one 5v reg but at the moment all seems well.
Next comes some glue gun action to tidy things up, then it goes into the box pictured or a very similar one along with the prop etc.
Graham
Think I may try it myself.
Wonder how much room the new QFP44 board and this hack takes up?
Parallel processing PDA anyone?
The viewfinders for cameras are a similar type, smaller ones on still, bigger on video cameras.
Touch screen for on screen keyboard?
How much are those Laser projected keyboards?
Gavin
Do you think it possible to still stuff it back into the OEM box?
I, too, would like to do this, since I don't care much for sound at this point. Would you be so kind as to document the changes??? [noparse]:)[/noparse])
-Parsko
PS- Glue guns. Another one of those indespensible $5 purchases in a hobbiests' life!
The audio board can be removed easily and the two wires that go to the LEDs are also accessable without taking the whole screen out. Disconnecting the 5v regulator on the LCD board might be more difficult as it is on the LCD side and the wires to the copper screening sheet that lies between are quite short, however it could be done with care. The 5v regulator is marked 7805, don't confuse it with the 20v one, 7820. The 5v leg is next to a small pad marked 5v. The best thing to do is cut the leg then desolder the bit stuck to the pad as they dissipate so much heat that desoldering can tend to end up damaging the board. Add your 5v line to that and also connect it to the 5v that will go to the two potentiometers that set colour and brightness. You also need ground for the pots and two wires that go to the PCB where it is marked as colour and bright. It should be self explanitory which pin is which, note that they have extra resistors to limit the range of voltages they produce.
I wish I had another screen then I could take pictures as I went along, I like to document things like this but I was not all that confident when I started.
I can see what I can do. I have a 7" screen that needs a similar treatment (except the back light is OK) but I'll be doing a better job of the docs on that one I hope.
Graham