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What do I need?

flyingferret

New member
I am rather new to LCDs. I am in the process of doing a case mod, and think an LCD would be very cool. But I do not know anything about hooking them up. Blue LCD is really the only option. So what do I need: hardware, software, etc?

I have some general electronic knowledge, but not much in the area of LCDs. I have no idea about the interfaces. Any information you could give me would be appreciated. I am willing to put the work into making my case that much more unique and this looks like the way to do it.

Thanks

Malachi
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CF Tech

Administrator
The blue lcd we have is a is a parallel/standard/HD44780 style LCD module.

You generally want to select your software, then find an LCD and schematic that suit it.

There are programs that will drive parallel LCDs from a PC's printer port. LCDproc (Linux) will.

There is a thread here that gives a schematic. However, see the comment in this thread about backlights and potentiometers.

Here is an MP3 Player that uses a plugin to allow WinAmp to drive a parallel LCD.

Here is a page about 44780 based LCD's in general.

I have a utility (lcdprint.exe) written by Mike Lynch that will send a text file to a display. That can be good for debugging your cable.

There is a pretty good tutorial on connecting a parallel LCD at http://mpford.dyndns.org. Then click on "LCD Display", and then " Step by Step how to build an LCD Display" (it is a framed site).

There is another nice article here that shows connection in a PC, and yet another.

You can also search our forum for "parallel".
 

flyingferret

New member
Thank you for your help. I have definitely decided on CFAH1602B-TMC-JP and will using LCD driver and one other winamp pluginBut I don't understand one thing. I understand all the data connections, they seem pretty simple. However the power supply situation is confusing me.

Your advice in the thread about potentiometers seems to contrdict the schematic published by LCDdriver author. Can you tell me what components I need to hook up power?

I don't understand why the schematic uses a 10K pot to VLc, is that for brightness/contrast? And why is there a 100 pot on the ground leg of VB- ? You say not to use a pot, and anyway, isn't regulating a ground always a no-no. I thought you always wanted to regulate the supply?

Please advise on these issues. I will order parts as soon as I get it all figured out.

Malachi
 

CF Tech

Administrator
The 10K pot on Vlcd is fine--and recommended. It sets the viewing angle (commonly referred to as "contrast").

The 100ohm pot on the LED is what is scary. It that is turned to 0 ohms for even a short time, you can over-current and damage the LEDs in the backlight. It will work, but on a ultra low impedance (strong) supply (like a PC's +5v line) you really risk toasting the LEDs.

If you do not want to dim the backlight, then just follow the backlight calculations . If you want to add a dimmer, put the 100ohm pot in series with the fixed resistor determined from those calculations, so if the pot is turned to 0 ohms, the current will still be limited to within the maximum the LEDs can handle.

Variable:
+5v---POT---RESISTOR---(A=+)LED(K=-)---GROUND

Fixed:
+5v---RESISTOR---(A=+)LED(K=-)---GROUND

The order really does not matter, they are all in series and all see the same current (which is all that LEDs care about). So these are equivalent:

Variable:
+5v---(A=+)LED(K=-)---POT---RESISTOR---GROUND

Fixed:
+5v---(A=+)LED(K=-)---RESISTOR---GROUND
 

flyingferret

New member
Thanks

Thank you for all your help. You guys are awesome, I don't think I would buy an lcd from anyone else. You have answered all my questions.

From the spec sheet on the CFAH1602B-TMC-JP I know:

Vled = 3.3V, Iled = 25mA
So R=(5V-3.3V)/.025 = 68ohms

That is a common rating and the desired power rating is:
Presistor=.025*(5V-3.3V) = 0.0425w

So, I plan on using a 68ohm resistor rated at no less than 1/4w.

I am guessing that a 100ohm pot will be plenty to adjust the backlight, I am not sure how to figure what value would bring it down to 0, so I will just go with a 100ohm, since everyone suggested that one in the first place. Thanks again for all your help. I will order parts in the morning.

Malachi
 

flyingferret

New member
Okay, my LCD gets here tomorrow. I think I have everything together. But I have one final question. I have the CFAH1602B-TMC-JP. I am finding two different scematics for wiring. They are identical, except for one pin.

http://www.ocmod.com/img/articles/lcd01/sch01b.gif suggests using Parallel pin 17 to connect to LCD pin 4.

http://www.markuszehnder.ch/projects/lcdplugin/images/lcd_parallel_8bit.gif suggests using Parallel 16 to connect to LCD pin 4.

They are both supposedly for universal 44780 based LCD's. Which one is correct?

Malachi
 

flyingferret

New member
Now I am posting again within 20 minutes of my last post. I am still not sure, but beginning to think that pin 16/17 don't really matter.

A second article at OCMOD http://www.ocmod.com/code/show_art.php?id=27&pg=1 now mentions 'a different way' to wire the LCD. It shows pin 16 to LCD pin 4. The author gives no indication why he switched to the other pin, he just makes it sound like you can do it either way? Any ideas?

Malachi
 

flyingferret

New member
This is my last post tonight, I promise:) One other difference between the two schematics listed in my first post of the night, is that in one Parallel pin 14 connects to LCD pin 5 R/W. The other diagram lists LCD pin R/W as a ground. Which is right? How could a ground supply a H/L signal?

Okay, that is everything I can possibly think of. If I can ever figure out how to wire this freaking thing it will kick ass :)

Malachi
 

ip_freely

New member
i wussed out and got a 16x2 serial (632) where all you do is plug and play :D

unfortunatley you forfiet color choices :(
 

"?"

New member
Im with IP_freely hehehe ill get the 20X4 when avaliable heheh dont want to deal with parrllel heheheh


"?":D
 

flyingferret

New member
Well, hopefully the administrator will have some ideas. I did not do serial because a) I enjoy tinkering with stuff and b) I wanted blue or nothing at all.

I don't mind tinkering with stuff I just usually like it when there i s a standard and not conflicting info. But so far the administrator has been very very helpful.

Malachi
 

CF Tech

Administrator
Especially with the parallel displays: "You generally want to select your software, then find an LCD and schematic that suit it. "

However you hook them up, it is worthless if the software does not support that connection.

So find the software that does what you want, then connect it to the schematic that the software recommends.

The R/W (+5v = read, 0cv = write) is grounded in some applications because that designed saw no reason to ever read from the LCD.
 

flyingferret

New member
Well, thanks for reminding me of your earlier advice. I was simply trying to verify this statement "This is the hookup for every other Windows-based 44780 software, and there are patches out there to let lcdproc use this wireup under Linux." made by Ryan "Uller" Myers in
this thread you reffered me to. He is a programmer of drivers, but apparently that statement is not correct.

Having gathered that there is not a reasonable facsimile to a standard I will use the schematic that Uller provided. That appears to be used more than the others, which apparently are smoking the proverbial crackpipe. I am really beginning to see the advantage of serial communications. However, until a blue serial lcd comes out, I will stick with this. My only other option would be to use a backpack, and then the whole wiring debate starts again...

I order some blue switches to match the LCD, once the get here, I will cross my fingers and hope for the best.

Malachi
 
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