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Forum Index : Microcontroller and PC projects : MM 20x4 display

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palcal

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Joined: 12/10/2011
Location: Australia
Posts: 1805
Posted: 09:36pm 16 Jul 2013
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Hi All,
I've been trying to get a 20x4 display working on a project and finally found I had read the pull up resistor code backwards and used 120 ohm instead of 10K. The current would have been about 40ma through the 120 ohms. As the display still won't work the question is would the open collectors be RS.
Paul.
"It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all"
 
bigmik

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Joined: 20/06/2011
Location: Australia
Posts: 2870
Posted: 09:46pm 16 Jul 2013
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Hi Palcal.

Unlikely.... Why not try using digital out (not OC) on your pins?

When I first mucked around with Geoff's original example code I couldnt get the OC outputs to work with a 16x2 LCD (yes with appropriate Pull Ups) so I changed the code to use Digital out ie. SETPIN(x),8 (instead of 9) and it worked fine.

Regards,

Mick

Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<<
 
djuqa

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Joined: 23/11/2011
Location: Australia
Posts: 447
Posted: 09:48pm 16 Jul 2013
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I use those 20x4 displays all the time and use just the standard values except used digital output same as bigmik

Edited by djuqa 2013-07-18
VK4MU MicroController Units
 
palcal

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Joined: 12/10/2011
Location: Australia
Posts: 1805
Posted: 10:04pm 16 Jul 2013
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Well now I'm confused, what do you mean by just the standard values except digital output. Mick says he uses digital output
Paul.
"It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all"
 
djuqa

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Joined: 23/11/2011
Location: Australia
Posts: 447
Posted: 10:06pm 16 Jul 2013
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  palcal said   Well now I'm confused, what do you mean by just the standard values
Paul.

Standard values for the pullups, voltages, settings, codes . in other words everything exactly the same as using 16x2 display example in library.
Just making the adjustment for the extra lines, chars in the software.

Edited by djuqa 2013-07-18
VK4MU MicroController Units
 
kiiid

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Joined: 11/05/2013
Location: United Kingdom
Posts: 671
Posted: 10:11pm 16 Jul 2013
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These are very simple to use. In 4-bit mode you will only need D4-D7, E and RS connected to your micro. These all go to normal outputs from the micro and don't need any pull-up/pull-downs. Connect D0-D3 to ground. That's all. The commands and initialisation should be as per the LCD's datasheet.
http://rittle.org

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palcal

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Joined: 12/10/2011
Location: Australia
Posts: 1805
Posted: 10:24pm 16 Jul 2013
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Thanks especially to Mick, all I had to do was use the Digital Out instead of Open Collector. After days of trying to get it to work all I had to do was remove the pull ups and change a 9 to an 8.
Thanks All
Paul
"It is better to be ignorant and ask a stupid question than to be plain Stupid and not ask at all"
 
James_From_Canb

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Joined: 19/06/2011
Location: Australia
Posts: 265
Posted: 01:36pm 19 Jul 2013
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Can anyone thing of a reason why the pull-up configuration didn't work?

I know misconfiguration is one possibility, but some experienced people have had problems that were resolved once the pull-ups were removed and the mode changed. It seems unlikely that they couldn't/didn't follow the diagram correctly.

I've tested at least 5 different LCD screens from different suppliers on the same circuit with no big problems. The only issues were having to adjust the contrast so I could see the characters, and adding a small delay between lines of data being sent to the LCD to stop gibberish being displayed.

So, can anyone give any suggestions why the pull-up configuration occasionally does not work?

Also, is there any advantage to the pull-up configuration over the non pull-up configuration?

Just curious.

James
My mind is aglow with whirling, transient nodes of thought careening through a cosmic vapor of invention.

Hedley Lamarr, Blazing Saddles (1974)
 
bigmik

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Joined: 20/06/2011
Location: Australia
Posts: 2870
Posted: 02:45pm 19 Jul 2013
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Hi James,

  James_From_Canb said   Can anyone thing of a reason why the pull-up configuration didn't work?


That is a tough one... It could be that the displays are generally 5V and the MM is 3.3 and OC just doesnt quite offer enough `Drive' when supplied by 3.3V... All I know is that in my case OC didnt work but Digital DID.


  James_From_Canb said  
Also, is there any advantage to the pull-up configuration over the non pull-up configuration?


With Open Collector the High is basically provided by the PULL-UP resistor itself and the LOW is the chip which overrides the PULL-UP. This enables several OC sources to trigger the same input (ie. any one or more can drive the chip with out harming the other devices connected) Like PC PS2 keyboards, you can parallel 2 up and both will work that is how some external keypads work...

Not sure I have described that well... I am sure that's as clear as mud...

Regards,

Mick
Edited by bigmik 2013-07-21
Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<<
 
James_From_Canb

Senior Member

Joined: 19/06/2011
Location: Australia
Posts: 265
Posted: 05:04pm 19 Jul 2013
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Doesn't Open Collector make the Maximite sink 5V, so the LCD control pins get 5V?
Using the Maximite digital outputs would provide 3.3V to the LCD control pins.
The HD44780 spec sheets says both voltages are OK, but there are Internet discussions about Sparkfun LCD units that are specifically 3.3V. Maybe there are others that work with 3.3V and not 5V.

Anyway, it looks like the lesson is to try the simple way first, without the pull-up resistors, unless someone can explain why the OC solution is better.

James
My mind is aglow with whirling, transient nodes of thought careening through a cosmic vapor of invention.

Hedley Lamarr, Blazing Saddles (1974)
 
MicroBlocks

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Joined: 12/05/2012
Location: Thailand
Posts: 2209
Posted: 08:43pm 19 Jul 2013
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In case of an LCD:
OC should not be better or worse and both digital and OC should work.
OC is the only way to get a 5v device to work.

Maybe not the right pull ups?
I use 4k7 ohm and those work with other 5v devices using OC.
Microblocks. Build with logic.
 
bigmik

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Joined: 20/06/2011
Location: Australia
Posts: 2870
Posted: 09:38pm 19 Jul 2013
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Hi TZ,

I cant remember what pull ups I actually used but my usual is 1k for a Pull down and 4k7 when pulled up unless I only want a weak pullup where I tend to use 10k.

Regards,

Mick


Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<<
 
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