Computing stuff tied to the physical world

GLCD on battery power

In Hardware on Nov 27, 2010 at 00:01

I’m going to switch to a different type of graphic LCD once the next batch of Graphic Boards arrives. Instead of a white-on-black type, the new GLCD will be a blue-on-sort-of-blueish color:

Dsc 2356

The reason for this is that it is still quite readable without the backlight:

Dsc 2358

There is a solder jumper on the Graphics Board, to choose between powering the backlight continuously via PWR, or having it powered under software control, via the not-often-used IRQ pin. This not only lets you turn the backlight on and off, but even dim it under software control, because the IRQ pin supports PWM, i.e. analogWrite().

The above display draws about 280 µA without backlight right now, which means it will keep running for over a month on a single AA cell, using the AA Power Board. There are probably ways to reduce that current consumption further, as I’m not doing anything yet with the ST7565’s standby and other low-power modes.

And although it may not be practical for a permament display, this definitely is useful for something I’d like to have around and use on a regular basis. By sending it stuff to display over wireless, this setup can support what is quickly becoming my favorite mode of operation here at Jee Labs: no wires cluttering my desk!!!

  1. If you could find a way of powering it up only when someone’s eyes are directed at it, you’d certainly have something there.

  2. If the user is like me, and isn’t wearing his glasses, he would have to get within about a foot of the display to read it. Close enough for a capacitive sensor with a large antenna to detect. I think those can draw well under 100 uA quiescent. But, if you have a PIR detector running anyway as part of your system, might as well use that.

  3. A (home made?) IR-LED based distance detector (like GP2Y0A21YK0F)? Turned on very briefly every second by a stand alone circuit consisting of a “timer” and a comparator that wakes up the JeeNode on detecting something? Hummm, it conflicts the PWM use of the IRQ pin.

  4. Thanks for the Discover Circuits – lots of interesting ones on that site!

    I found this one which senses changes in the electric field: http://www.imagineeringezine.com/e-zine/efield.html

    No idea about power draw, but it runs off a 9V battery so it’s probably low. Maybe some newer op-amp could be used.

  5. When will you try a e-Ink display? For sure you’ll can keep it running with one AA for a lot of month!

  6. Although a “gaze sensor” would be a nice touch, there is definitely something to be said for the functional equivalent of the “low-power screen-saver” on a PC.

    We’re all used to having to wiggle the mouse, or hit the “shift” to get a display to wake up. Perhaps a simple button-press would do, or a hand-wave over an IR or LDR sensor?

    I guess it uses up a precious IO though…

  7. I see the kit back in the shop, is this now with this new LCD or with the old blue one?

    • Ah, yes – it’s indeed the new blue/black on white one. I’ve added a note and will update the pictures later today. Thx.

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