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Calamar
Joined: 07 Sep 2003
Posts: 60
Location: Buenos Aires (Argentina)
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| low power consumption lcd |
 Posted: Thu Dec 09, 2004 10:04 pm |
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For a battery powered proyect
I need a low power consumption diplay
( 2 lines and 6 or 8 digits) alphanumeric,
less than 50 microA, I must use a driver ??
someone used a 14 or 16
segment display (6 or 8 digits display)
, which one ???
there isnt lcd module with low consumption ??
Best regards
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Best Regards
Daniel H. Sagarra
La Plata (Argentina) |
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Will Reeve
Joined: 30 Oct 2003
Posts: 209
Location: Norfolk, England
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| Posted: Fri Dec 10, 2004 3:44 am |
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I use a 16 x 2 line LCD from Powertip for one of my products (run off 3 x AAs). I used a PIC pin to power the LCD display. As long as you don't use a backlight it costs 2mA of current to run the display. I searched high and low for a less hungry LCD but can’t find one for sensible money as my project was almost a throwaway design so used a 'screen saver' approach and only switched on the display when I really had to!
If you can splash out 30 quid you can get a 100 x 32 pixel graphics LCD display which only consumes 100uA; still double your spec. It’s a DMX973B by Lascar.
If you find a solution please let us know,
Keep well,
Will |
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Calamar
Joined: 07 Sep 2003
Posts: 60
Location: Buenos Aires (Argentina)
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Mark
Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA
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| Posted: Sun Dec 12, 2004 6:01 pm |
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| You do realize that is only the glass. You have to have a controller. |
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rwyoung
Joined: 12 Nov 2003
Posts: 563
Location: Lawrence, KS USA
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| Posted: Mon Dec 13, 2004 8:37 am |
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http://www.pacificdisplay.com/cdm/CDM-08200.pdf
This is Pacific Display's 2x8 alphanumeric with controller. Typical current (without backlight) is 1.38mA, maximum is 3mA.
The link you posted is for "glass only" displays. Two problems you might encounter, first no controller so you will need to mux the signals yourself. Second most (if not all) of those displays are fixed icon/segment types, not pixel or character based.
If power consumption is an issue and you can spare an I/O pin to either run the display's Vdd or drive the gate on a MOSFET, then you can turn off the display when not needed. Turn it back on and re-initialize when next needed.
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Rob Young
The Screw-Up Fairy may just visit you but he has crashed on my couch for the last month! |
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jds-pic
Joined: 17 Sep 2003
Posts: 205
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rwyoung
Joined: 12 Nov 2003
Posts: 563
Location: Lawrence, KS USA
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| Re: low power consumption lcd |
| Posted: Wed Dec 15, 2004 9:01 am |
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Very neat part. Have you tested it at 5V (datasheet says Vdd=6Vmaximum) or are you running at the recommended 3V?
Also, what is the contrast range like with and without the use of a negative supply?
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Rob Young
The Screw-Up Fairy may just visit you but he has crashed on my couch for the last month! |
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jds-pic
Joined: 17 Sep 2003
Posts: 205
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| Re: low power consumption lcd |
| Posted: Wed Dec 15, 2004 9:44 am |
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| rwyoung wrote: |
Very neat part. Have you tested it at 5V (datasheet says Vdd=6Vmaximum) or are you running at the recommended 3V?
Also, what is the contrast range like with and without the use of a negative supply? |
it is a very neat part. there are a multitude of ways to conserve power with it; for example, you can put it in static mode and turn off the internal oscillator. the info on the LCD stays up but power drops considerably as the microcontroller is not running.
i have not tried it at 5V; the project i used this display on was battery powered from a single CR123 3V lithium battery, which was used as input to a 1.2->3V input / 3.3V output hi-eff DC-DC converter circuit. that in turn fed the PIC (LF series) and the LCD, among other things.
you need a negative bias for the LCD. there are a couple of ways to do it...
the datasheets for the controller and LCD confused me for a while; the controller seems to have all of the hooks for doing on-board charge pumping for the negative rail. i guess this would work on a PCB-based design where you can actually have caps nearby. but the LCD unit itself is COG (chip on glass) and there is no way to mount caps. the LCD cable *seemed* to bring out *most* of the required pins but i could never figure out exactly how they expected you to connect the external charge pump caps. in my design, a couple inches away from the LCD sat a MAX232-derivative which provided my widget with comms to a PC. hence i got the idea of stealing -10V from the charge pump on the MAX232. i fed that into a pot (so i could adjust the voltage to the LCD and therefore the contrast). i was hyper-paranoid that the switching noise from the MAX232 was going to manifest itself in the LCD, or that when i sent RS232 data the same would happen. these fears were unfounded. even without ANY filtering there were no artifacts on the display. i had a hard time measuring just how much current was being drawn by the LCD bias ciruit. my best HP 6 digit benchtop DMM showed it to be just a few uA. so i don't think that the MAX232 even knows it's there, and on the flip side the LCD seems to be immune to any type of switching noise as well. you may want to RC or LC filter it just in case, but i really don't think it's necessary.
i'm quite sure that you can use the LCD unit in conjunction with external caps to self-gen the negative bias. this way you only need a single 3.3V supply rail. it will take some RTFM and perhaps contacting the LCD vendor for some info.
jds-pic |
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rwyoung
Joined: 12 Nov 2003
Posts: 563
Location: Lawrence, KS USA
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| Re: low power consumption lcd |
| Posted: Wed Dec 15, 2004 11:53 am |
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[quote="jds-pici got the idea of stealing -10V from the charge pump on the MAX232.
jds-pic[/quote]
I've done that before. Works pretty well. I remember reading either in a Maxim IC app. note or one of the Max232 datasheets about how to size the caps if you are going to be "stealing" current from one of the charge pumps.
It does inject noise into that rail at the MAX232's switching frequency like you suspected. For an LCD bias, I doubt it makes much difference or that much current is drawn. Your suggestion of a simple LC or RC filter should work fine.
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Rob Young
The Screw-Up Fairy may just visit you but he has crashed on my couch for the last month! |
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