I currently have a standard HD44780 compatible display hooked up to my Uno but I would prefer more digital IO pins (due to the Ethernet shield I'm also using). I know I could get an I2C backpack from Adafruit for my current LCD but I would prefer to keep it as is for possible future use. Is eBay the only source for I2C LCDs? Specifically 20x4 ones as that is what would work best for my current project. Considering this one. I am naturally impatient and don't really want to wait that long either (Jan 18th - 28th estimated delivery).
The ebay link you provided doesn't work for me.
I have several different i2c backpacks that I've gotten from ebay.
Haven't had any issues with them working.
Lots of people have issues getting them to work,
but it really isn't that difficult to get them working if using fm's library.
There are only 4 combinations of wiring and I have a guesser
sketch that can also help figure out the constructor parameters.
I also have the adafruit backpack and I'm not really a fan of it for few reasons.
It doesn't use a normal 4 pin header which makes hooking up the wires to it a bit
of pain since you can use a nice simple 4 pin header.
All the "duino" boards and shields I use have a 4 pin i2c header so
connection with a 4 pin header/cable is really easy.
For i2c, the AdaFruit backpack uses a mcp23008 chip vs a PCF8574.
The mcp23008 will always be slower than the PCF8574 due to its inherent
way of communicating. Adafruit's library is REALLY slow compared to what
is possible, because of the way they implemented it.
And while I have written an i2c module that supports both the mcp23008 and
the PCF8574 chips for fm's library, that has significantly much better performance
it isn't yet available.
There are also some i2c based LCDs that don't use a backpack so be careful
which devices you are looking at. (I can't tell since the link wasn't working).
--- bill
smccloud:
Is eBay the only source for I2C LCDs?
No, but you might pay a lot more if you buy them somewhere else.
bperrybap:
The ebay link you provided doesn't work for me.I have several different i2c backpacks that I've gotten from ebay.
Haven't had any issues with them working.
Lots of people have issues getting them to work,
but it really isn't that difficult to get them working if using fm's library.
There are only 4 combinations of wiring and I have a guesser
sketch that can also help figure out the constructor parameters.I also have the adafruit backpack and I'm not really a fan of it for few reasons.
It doesn't use a normal 4 pin header which makes hooking up the wires to it a bit
of pain since you can use a nice simple 4 pin header.
All the "duino" boards and shields I use have a 4 pin i2c header so
connection with a 4 pin header/cable is really easy.For i2c, the AdaFruit backpack uses a mcp23008 chip vs a PCF8574.
The mcp23008 will always be slower than the PCF8574 due to its inherent
way of communicating. Adafruit's library is REALLY slow compared to what
is possible, because of the way they implemented it.
And while I have written an i2c module that supports both the mcp23008 and
the PCF8574 chips for fm's library, that has significantly much better performance
it isn't yet available.There are also some i2c based LCDs that don't use a backpack so be careful
which devices you are looking at. (I can't tell since the link wasn't working).--- bill
Let me try the link again, somehow it ended up with some extra characters. It does have a backpack but I cannot tell which chip on it.
I ordered one and some male to female jumper wires. I will update you guys on how it works once I get it.
Another question, does it matter if I use A4 & A5 vs the dedicated I2C pins on an Uno R3? Or does using the dedicated pins mean I still cannot use A4 & A5?
smccloud:
Another question, does it matter if I use A4 & A5 vs the dedicated I2C pins on an Uno R3? Or does using the dedicated pins mean I still cannot use A4 & A5?
They're the same thing, they're physically wired together on the PCB.
fungus:
smccloud:
Another question, does it matter if I use A4 & A5 vs the dedicated I2C pins on an Uno R3? Or does using the dedicated pins mean I still cannot use A4 & A5?They're the same thing, they're physically wired together on the PCB.
Then I will use A4 & A5. Not having to use 6 digital pins to control my LCD will allow me to wire my project better anyway.
smccloud:
I ordered one and some male to female jumper wires. I will update you guys on how it works once I get it.
That will be a PCF8574.
The way you can tell is that a PCF8574 has 16 pins and a MCP23008 has 18 pins.
When you are ready to use it, I'd recommend using fm's library.
Then it is just a matter of filling in the constructor to tell the library
the i2c address and how the chip is wired up to the LCD and backlight.
--- bill
that is correct.
Thanks for the help. Now to wait (impatiently) for the parts to arrive.
I have that exact display and just posted a help thread.
It responds on the ox27 address but other then that it seems dead with no backlight or chars on the display.
Did you ever order one and if so what contructor line did you use.
I am using the Above recommend lib also.
Highflier
highflier:
I have that exact display and just posted a help thread.
It responds on the ox27 address but other then that it seems dead with no backlight or chars on the display.Did you ever order one and if so what contructor line did you use.
I am using the Above recommend lib also.
Highflier
I ordered one, it just made it to the US yesterday. At the normal rate of USPS, I should have it in 2 more weeks (I hope).
OK well I made some headway, I am starting to think that my Backlight is f'd up.
I can see chars on the screen but only if I shine a flashlight at it. Also I can tell the back-light is trying to light up as the color around the chars does also a tad, but only visible when I am using the flashlight. So at the moment it is virtually useless as I am not going to grab a flashlight every time I want to see what is on the screen.
Trying to figure out what to try next. I hope yours works for you, I can tell you that the sample code they link to looks to be good. I just needed a flashlight to confirm it 
Highflier
highflier,
Don't double post.
lets keep discussion about your board, on your thread.
--- bill
Sorry since he had the same board I thought I would update him. If you have more questions just see my other thread.
Highflier