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Topic: Negative voltage (Read 3659 times) previous topic - next topic

Osgeld

Aug 15, 2010, 04:49 am Last Edit: Aug 15, 2010, 04:55 am by Osgeld Reason: 1
I recently got a LCD module as it was headed to the trash at work (cause the touch screen was smashed, which is just a add on module) I intended to be half way though a library by now, but after making a ribbon cable breakout header and blah blah blah ...

Its one of those units that require a negative voltage to drive the optics!

blah, ok I have a chip that takes 5v and inverts it to -5, so I know they exist, but I really didn't want to wait an extra half week to get a smd model (cause that was all that is available) for the voltages needed (up to -18)

goggling around  I saw a few different ways of doing it, 1 using a 4000 chip (dont remember off hand) and another using a handful of pnp resistors, all seemed like a pita until I found this one which just uses a 555 timer, a couple extra caps and a couple of diodes (which can run upto 15 volts which is close enough for contrast)

http://www.csgnetwork.com/ne555c1.html

so I made it up, not using the recommended components (10nf vs 1, 330uf vs 470, 2k2 vs 2k, and for the diodes I used some standard "power" silicon types) and while not perfect, and I am loosing a little using the silicon diodes, I have to say it is doing the job just fine

so check it out if you have the need
http://arduino.cc/forum/index.php?action=unread;boards=2,3,4,5,67,6,7,8,9,10,11,66,12,13,15,14,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,86,87,89,1;ALL

TchnclFl

I've never really looked into it, but I just don't get negative voltage...

Isn't it just a power supply connected backwards? :P

</ignorance>

Osgeld

#2
Aug 15, 2010, 05:13 am Last Edit: Aug 15, 2010, 05:16 am by Osgeld Reason: 1
yea but how do you wire a power supply both backwards and frontwards at the same time :) (ok its super easy if your using an AC source or batteries, but from a DC wall wart)

btw you would get a kick out of this, its a 240x64 glcd
http://arduino.cc/forum/index.php?action=unread;boards=2,3,4,5,67,6,7,8,9,10,11,66,12,13,15,14,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,86,87,89,1;ALL

TchnclFl

Quote
its a 240x64 glcd


:O cool!  You'll have to post about it some time.  What's the chipset?  It's funny that I keep telling myself I shouldn't spend ~20 bucks on stuff I don't need (GLCD), and then I find myself placing a $25 dollar order for things I DEFINITELY don't need :P.

Osgeld

its using a toshiba T6963C chipset

and here is a pic from google images
http://arduino.cc/forum/index.php?action=unread;boards=2,3,4,5,67,6,7,8,9,10,11,66,12,13,15,14,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,86,87,89,1;ALL

UltraMagnus

Quote
I've never really looked into it, but I just don't get negative voltage...

Isn't it just a power supply connected backwards? Tongue

</ignorance>


kind of, I think the easiest example is a centre tap on a battery connected as ground, the negative end would then become a negative voltage.

Quote
yea but how do you wire a power supply both backwards and frontwards at the same time Smiley (ok its super easy if your using an AC source or batteries, but from a DC wall wart)


Use two wall warts, or a dual isolated output one, connect them in series and use the centre wire that you just connected as ground.

mowcius

Quote
Isn't it just a power supply connected backwards?

Umm, nope

Quote
It's funny that I keep telling myself I shouldn't spend ~20 bucks on stuff I don't need (GLCD), and then I find myself placing a $25 dollar order for things I DEFINITELY don't need

Well you know you need one of these:
http://cgi.ebay.co.uk/ART-USED-LCD-graphical-640x480-mono-8-4-EG9018C-/390223734243?pt=LH_DefaultDomain_212


about $12 including postage or something...

deSilva

#7
Aug 15, 2010, 02:24 pm Last Edit: Aug 15, 2010, 04:14 pm by mpeuser Reason: 1
Quote
...until I found this one which just uses a 555 timer, a couple extra caps and a couple of diodes (which can run upto 15 volts which is close enough for contrast)


Where did you get the +15V from in the first place?
The 555 will just produce some square waves, which can also be produced by a spare Arduino PWM pin... As this will give you -5V only @10mA (whilst the 555 can deliver 100mA) an all purpose NPN transistor is also needed, collector to the higher + voltage.

For peeople interested in this: http://www.holger-klabunde.de/dcdc/picdcdc.htm
It is not English but you need not understand the text, it's all in the diagrams :-)

TchnclFl

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Well you know you need one of these:


That's AWESOME!  Any idea if it's EVER been interfaced to Arduino?  :P  I suppose it'd be a challenge, but I'd probably fail haha

Osgeld

#9
Aug 15, 2010, 08:37 pm Last Edit: Aug 15, 2010, 08:40 pm by Osgeld Reason: 1
Quote
Where did you get the +15V from in the first place?


Im not, im dumping +12v from a wallwart

this thing is expects -18 for its darkest contrast, which is also useless cause then the screen is black, at -9 the contrast is actually just about perfect at -5 its barley visible unless the backlight is off and you hold it at a perfect angle

If I could have ran it off of -5 that would have been convenient, but nope, -11.x while not opaque is more than enough to blacken the entire screen  and have plenty of room for adjustment
http://arduino.cc/forum/index.php?action=unread;boards=2,3,4,5,67,6,7,8,9,10,11,66,12,13,15,14,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,86,87,89,1;ALL

zachwiej

Please tel me that someone did run that lcd on arduino!

copiertalk

arent you going to need some type of HVT to run the CCFL?

TchnclFl

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arent you going to need some type of HVT to run the CCFL


Good catch.  I hadn't noticed that it had a CCFL.

mowcius

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Good catch.  I hadn't noticed that it had a CCFL.

http://*Negative voltage generator on board
*Inverter for CCFT on board

It's in the pic.

You only need 5v and 5v logic but the arduino would be a bit slow. Nobody has tried it with an arduino yet as far as I know but if I remember, i'll buy one in a few weeks. I doubt I'd get very far though. We need one of our resident LCD experts to buy one!  :D

Mowcius

TchnclFl

#14
Aug 15, 2010, 11:18 pm Last Edit: Aug 15, 2010, 11:26 pm by Tchnclfl Reason: 1
Quote
*Negative voltage generator on board
*Inverter for CCFT on board


Again, nice catch ;).  I need to read more carefully before posting.  Yeah, I know NOTHING about how LCDs process data, so I'd be a bad one to experiment.  So you don't even need any high (positive) voltages for the LCD drive?

I'm going to post a thread here in Bar Sport asking people who know what they're doing to please try it out ;D

[edit]http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1281907513/0[/edit]

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