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PostPosted: Thu Oct 17, 2002 2:17 
ADMIN EDIT: If you're not familiar working with mains power don't even consider this option, please. Anyway in some situations this can be a good option.
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There are many ways to get -8v for the LCD display. Some ppl use the computer PSU (-12v and a pot), some use a charge pump (expensive and complicated).

A simple way that worked for me was to use a mains transformer (2 tailed), a bridge recitfier, a +5v volatge reulator (LM7805) and a -9v volatage regulator(LM7909). You will also need some caps to smooth out the voltages a bit. All easily accessible from any good electronics shop.

The 2 talied transformer has two 12vAC leads and a ground(0v). Connect the 2 12vAC lead to the AC pins on the bridge rectifier. Using the 0v from the tranformer you should now have +12 and -12v between the 0v and the + and - pins on the rectifier respectively.

Use some caps (about 1000uF) to smooth out voltages as they will be unipolar sine waves from the recifier ( ie. vvvvv as opposed to ------- if you get what I mean).

Now use the +5 voltage reg on the +ve side (ie input from rectifier, GND from transformer, and output will be +5v) and -9v regulator on the -ve side (ie input from -ve side, GND from transformer, and output will be -9v).

This should now give you very smooth +5v, and -9v.

Use a pot to adjust the -9v for the display.

Worked a treat for me and much cheaper than charge pump and no risk of killing my hard drives or motherboard. :D

Good luck. :wink:

P.S. If you have no idea what a bridge rectifier is or how a voltage regulator works then you shouldn't be trying to make your own LCD display!! Quickly unplug your soldering iron and put it in a safe place where you will never be able to find it again. And don't plain with mains power.

Here is an ASCII picture....cut and paste and change to fixed pitch font (e.g. courier) to see the pic properly:

Code:
---  --12vAC---------------/\~
   )(                     /  \
   )(                    /    \
240)(                   /bridge\
AC ) ---0v----+       -< rect'r >+
or )(         |       | \      / |
110)(         |       |  \    /  |
AC )(         |       |   \  /   |
---  --12vAC--)-------)----\/~   |
              |       |          |
              |       |          |
              0V     -12V       +12V
              |       |          |
              +--+||--+----------)---- -12v--[LM7909]---------> -9v
              |  1000uF          |              |
              +----------||+-----+---- +12v-----)---[LM7805]--> +5v
              |        1000uF                   |       |
              +----------------------- 0v ------+-------+-----> GND


Hope this works for you. And usual disclaimer: anything goes wrong or you kill you LCD or yourself it is NOT my fault.


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 Post subject: Just an extra note.
PostPosted: Thu Oct 17, 2002 2:30 
You can use other transformers (multi tail eg. 12, 8, 0, 8, 12).

Make sure you get the polarity of the caps right (i.e. +ve to +ve side in the case of +12, and +v to 0v in the case of the -12 side).

If the volatge going into the regulator is much higher than the output (ie. you supply +24v to a 5v regulator) it will get very very hot. 8O You may need some sort of heat sink.

And PLEASE PLEASE PLEASE use a multimeter to check the voltages before you hook it up to your LCD! This is fairly obvious, but some people never learn. :oops:

Good luck, Marty. :wink:


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 Post subject:
PostPosted: Sun Apr 13, 2003 4:34 
I'm a electronic newbie. please forgive me I really want to wire Graphic lcd by myself but I have no idea what bridge rectifier is ?
Can you give me a IC number ?
I know about voltage regulator


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 Post subject:
PostPosted: Mon Apr 14, 2003 22:24 
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Joined: Sun May 05, 2002 22:05
Posts: 2063
Location: Lappeenranta, Finland
wu wrote:
I'm a electronic newbie. please forgive me I really want to wire Graphic lcd by myself but I have no idea what bridge rectifier is ?
Can you give me a IC number ?

Bridge rectifier is used to make DC from AC. I don't know part numbers but there are very many different types available.

If you don't know much about electronics you shouldn't be building this circuit as it is possible to kill yourself with it. Instead look into these for example: http://www.skippari.net/phpBB2/viewtopic.php?t=63


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 Post subject:
PostPosted: Tue Dec 07, 2004 23:44 
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Joined: Fri Dec 03, 2004 7:03
Posts: 201
Location: Sydney, Australia
Hmmm...

No reply from the Newbie.... Hope he didn't kill himself playing...

_________________
Syridian,
http://syridian.com


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PostPosted: Mon Nov 21, 2011 9:47 
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Joined: Wed Nov 09, 2011 3:39
Posts: 2
seems like this whole forums is spam.. shame good info here. I just use a sick arse resistive network with tapped ground :mrgreen:

edit you could always ditch the AC for a nub 24v wall wart bung tap it then use the 78xx79xx's

sry but think i'll leave the forums :( i see nothing but spam spam spam and ham


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