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)
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
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
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.
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
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.
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.
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
...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: DC-DC Wandler mit PIC
It is not English but you need not understand the text, it's all in the diagrams
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
*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!
*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
Here's the thing that's going to kick your butt on that large monocrome LCD - from the datasheet (page 11/13):
"Since this graphic display unit contains no reflesh RAM, it requires data and timing pulse inputs even for a static display"
Obviously they meant "refresh RAM"...
So - if you can figure out a way to store 640x480 monochrome pixels on an ATMega (it would require 38400 bytes of RAM for a frame at 1bpp) - you would be halfway there; the other big question is whether the ATMega could refresh the display fast enough and/or keep up with the timing requirements.
Seems like no matter how you did it, you would have to make some kind of external RAM display refresh system; even a 2560 doesn't have enough RAM.
(ok its super easy if your using an AC source or batteries, but from a DC wall wart)
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.
