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[on:]

Hey there,

First post, so I have an excuse to be a true noob

Actually i've done some electronics projects before and i would say i've got the hang of things beyond the basics. But... now i'm getting started with an Arduino project involving an LCD Display called ATM1602B. Manual can be found here: http://www.kjell.com/.mvc/Document/File?id=b6e33422-63ff-48be-b140-a04a0114d7ef

Now, this really shouldn't be a problem and i've got it working, but to be honest i think the wiring should be the other way around. My problem is with the backlight power. It says "+" on the last pin. And "-" on the one next to it. The manual states that i should connect 4,2V to the "+" and GND to the "-". But if i do so, it's dark. If i go the other way around, it lights up... And i'm so confused that i refuse to go on before i understand why. If i can get this wrong, i must be misunderstanding something basic. And then who knows what mistakes i'll make once i start plugging other things in

Please, somebody enlighten me

[Reply #1 on:]

Back lights can often be routed to either polarity by surface mount resistors and zero ohm links. Try and trace what you actually have.

[Reply #2 on:]

i'm sorry, i really don't understand the words you just typed... i learned this stuff in swedish so that might be the reason

[Reply #3 on:]

The displays with a single rows of 14 (or 16) pins at the upper left corner of the pc board are almost universally wired the same as one another, with pin 1 near the edge of the board and pin 14 (or 16) near the center.

Unfortunately those with a single row of pins in the lower left corner of the pc board, like yours, are not at all standard.  In your case the 14 LCD pins are numbered but the other two are not.  I hope you spotted the fact that pin 14 is at the edge of the pc board and pin 1 is nearer the center, but not at the end of the row.

If you look at the specification for the LED BACKLIGHT POWER SUPPLY you will see that they specify the typical value (TYPE in Chinglish) as 4.2v and the maximum value as 4.5v.  To me this is an indication that they are specifying what is known as the forward voltage drop of the LED when operating at the correct current.  In that case this is NOT a voltage that you supply to the backlight (in spite of the terminology in the 'DC Characteristics' section).

The data sheet shows conflicting and/or ambiguous LED connections in terms of + and -.  Using the diagram on page 2 I would connect the LED- pin to GND (pin 1 is right next to it) and connect the LED+ pin, through a 150 ohm resistor to +5v and see what happens.  If that doesn't work then reverse the + and - to (possibly) agree with the 'Description of Terminals' but do not leave out the resistor.

Don

[Reply #4 on:]

Yes i figured just the way you do that connecting my positive end (with a resistor in between) to the one that says "+" and negative to "-" would work. But it didn't, and just as you suggest, i tried the other way around. And that worked. So that's where my confusion comes in. I guess it's just the manual where they got it wrong?! Because now i've wired it "wrong" and i got the display up and running, displaying messages and working perfectly.

I also noticed, in the page with the display commands, that you can turn brinking on or off. Guess that says a lot about the accuracy of the manual.

Thanks for your replies! And if anyone has a different opinion, please let me know - if i'm wrong i want to know.