Hi all, Today i bought myself a Christmas pressie, a Varitronix 128x128 LED Backlit LCD (T6963C). I wired it up according to http://users.skynet.be/bk234359/LCD/Site/images/schemas/t6963c_z_fs.gif Ran into some problems: I hooked up the 10k pot for contrast to +5v and ground, and when the LCD didnt work i realised i need -12v... ? I read the ATX specifications for the PSU, and I saw that the blue wire on the ATX motherboad connector is -12v. So i did the pin trick on an old PSU, but it doesnt start up... I'm not sure if the PSU is broken or what... Anyways, time for my question: is there anyway to get -12v from an ATX PSU besides the -12v and -5v? I need to get it from the power connectors not in use in my pc, ie. the 4pin molexs or something! ? Thanks God Bless, Richard EDIT: Got the old PSU working Now if only the LCD would work. Backlight works but nothing on screen. If i press the "reset" button a line appears on the screen briefly? (I think i reversed the voltage to the lcd bymistake.. )
it doesn't have to be the actual -12 line, just a difference of 12v so..... If you wanted to, you could use 2 6v PSUs and you'd get a 12v difference, (-6v and 6v) so...................... you can use the 12+ line in the + side and 0v in the - side
Bruno_me: the trouble is that he has only has the one pin to apply the negative 12, the 0v will come from the ground thats used for the entire module. How come you can't just splice into the negative 12 rail from the PSU?
first of all: you'r PSU won't start because you don't have any load on it.. and if it's an atx you'll have to short the green wire to ground (i think)... you are thinking the right way, so if you get the PSU to start i guess it should work..
Hi, your trying to get your LCD bias voltage, this is used to control the contrast of the LCD, you might find that you have killed the LCD by putting it to +5v enless it was dioded of course. First off from my experaince a 100k is much better for gfx LCD control (because there is a PD of 12v, rather than say 5 that would get on most character ones). I was unable to find a MGL(S)-128128T LCD techinical datasheet, that tells you the optimum contrast and the maximum values. You might be able to take the -12v supply from the ATX power connector. The current required for this should be negligable, (thou it would be better if you used as larger pot as you can get away with, less current). Looking at the datasheet that has the dimensions, there was no pin name that sounded as thou it had the negative voltage generator hooked directly too it. Smilodon is right, to start an ATX power supply take the green line low. From memory I think its the purple wire that is always powered at 5v.
Thanks for all the help! I got the old PSU started by shorting out pin 14 & 15 i think. The LCD's not working.. I think i blew it. Reversed the polarity when i extended the power cable well there goes my money i guess. Maybe if i plead nicely, the supplier will exchange it for me. I found the pinout here: http://www.varitronix.com/catalog/lcm_spec/MGL(S)-128128T.pdf Couldn't find any more specific info for it from the manufacturer, so I hooked it up using: http://users.skynet.be/bk234359/LCD...t6963c_z_fs.gif. Hope you'all had a great Christmas God Bless, Richard
Hi yes i would bet on the LCD been damaged from that, might be a bit late now, but if your buying an LCD in future, i would make sure that you get one with a built in negative voltage generator, tends to save a lot of time and money (the delivery cost of a say maxim charge pump tends to be more than the differnce in LCD cost), that way one of the pins of the LCD has the drive voltage (-12v in this case) generated and applyed to a pin, so you can make your own contrast. I would highly recomend a http://www.eio.com/g2446ap.htm (and its cheap, ur old inverter would probably work fine for the ccfl
Monolithics... You could always resort to a monolithic regulator, like a 7905. These work exactly the same as the 78xx series, but they produce negative voltages. Bear in mind that they do have the same restrictions, in that the input voltage needs to be around 1.25V beyond your output. Obviously, this isn't an ideal solution, since you won't need anything close to the current these devices are designed to produce, and you won't get -12V (easily), but it should provide enough oomph to mostly do the trick Ali
You can use a ATX PSU, but it would need a load of some sort to work correctly. (Fan, motor, drive, etc...) Or frozencpu.com sells a loading resistor for running PSUs with nothing connected.
If you just need -12V - check out this circuit: http://www.maxim-ic.com/cookbook/powersupply/pdfs/1846-12B.pdf Maxim gives free samples too
I just remembered: you can draw -10V at very low current from most RS-232 level converter chips, since they (usually) involve charge pumps - this means that they convert +5V to +/-10V. I've actually used this method to get contrast for a character LCD panel, so it does work. This is really useful if your project involves serial comms anyway, since you'll already have the chip. Maxim make a range of RS-232 level converters, the MAX220 - MAX249 series. Also, some of the family don't require any external components to work (the MAX233 is one of these, as well as being the one I've used). I don't have a link to the datasheet handy, since I have a local copy, but you should be able to find it on Maxim's site. As always, there are alternatives available from other manufacturers, should you so desire. Ali
You could probably Nab it from the rs-232 DTS line or similar, the problem is its contrast so you want a nice stable supply. The ATX line is the best bet, or if your using a micro you can make your own charge pump on the PWM line. But in this case if you've hooked the -12v line to a +5v, it might very well be a dead parrot
