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Topic: Problem with interfacing an LCD with PCF8574N (Read 1 time) previous topic - next topic

Morpheous

Feb 20, 2011, 07:15 am Last Edit: Feb 20, 2011, 09:05 pm by Morpheous Reason: 1
Hi, I did a board based on the schematic shown on the attached picture. The first time i ran it it looks to work fine. On my second try it didn't work any more. I decided that there is some wire connection problem. I measure all of the connections. Everything looks normal. And the board sometime works sometime not. So I did another board and another one ( 3 of them) completly different parts. And the same problem. I'm using TI's PCF8574A, the schematic is for the NPX's chip. Is there any differeneces between them. May be TI's chip need pull-up resistor (I think I saw it somewhere...). Thanks!

floresta

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the schematic is for the NPX's chip.

Sorry, my crystal ball is out for repair.

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May be TI's chip need pull-up resistor (I think I saw it somewhere...).

That's the purpose of R2 and R3.

Don

Morpheous


Quote
the schematic is for the NPX's chip.

Sorry, my crystal ball is out for repair.


The schematic should be attached now ( don't know what happend). I mean pull-up resistor on the output PCF8574N's pins for D4-D7,E,R/W,RS. Like this one - http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1233786313/3#3

floresta

#3
Feb 20, 2011, 10:10 pm Last Edit: Feb 20, 2011, 10:13 pm by floresta Reason: 1
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The schematic should be attached now

It was attached before as well - how else could I have identified R2 and R3 without a crystal ball?

It was 'NXP' that had me confused since I didn't recognize the name.  I don't think that two ICs with the same part number would differ in the need for pull-up resistors on their I/O pins.  Neither datasheet mentions the need for external pull-ups so I doubt they are needed.  I do not see LCDs mentioned in the post to which you linked in your reply and I don't see a link to the library that it is using either.

I don't see a link to the library that you are using either so that could be the cause of your problem.  

Is your contrast potentiometer adjusted properly?

You mention that your circuit worked at one time but that it no longer works.  What exactly does it do when it 'doesn't work' ?  
 Is the display blank?
 Are strange characters displayed?
 Are the correct characters displayed in the wrong location?
 Do the characters appear upside down?
 Are the characters displayed from right to left?
 Is one line of blocks displayed?
 Do you understand why I miss my crystal ball?


Don

Morpheous

So, first the two I2C chips have same name (only different suffix). The LCD I'm using is 16x2 - RC1602B. It's not the first time I use an LCD, so the contrast potenciometer is not the problem 100%. The used library is in the attached archive. The LCD is not blank (somethimes is), but shows strange characters, sometimes some of the real characters are shown, but not on their location, or only some of them. The strange is that, after these anomalies, I power it up again and everything is OK. I hope you'll not need the crystal ball any more :)

Morpheous


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