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LCD HD44780 PCF8574T i2c Driver
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Ttelmah



Joined: 11 Mar 2010
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PostPosted: Sun May 21, 2017 8:16 am     Reply with quote

Makes total sense.
temtronic



Joined: 01 Jul 2010
Posts: 8278
Location: Greensville,Ontario

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PostPosted: Sun May 21, 2017 12:50 pm     Reply with quote

Gee Mr.T. I just don't underdstand it at all, the 'big picture' that is.

Using an I2C port expander doesn't make 'sense'. While you save 4 I/O pins, you've added a 16 pin device onto the PCB, so the PCB has to be bigger and more complex. Hmm... I'd just use a bigger PIC...
Also the LCD driver just got a tad more complicated, so more R&D time cutting/compiling/testing code
There's also the real additonal cost for the I2C device and PCB. Maybe not much, but it does add up.
It'll be interesting to see where this thread weaves next though !

Jay
PCM programmer



Joined: 06 Sep 2003
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PostPosted: Sun May 21, 2017 1:10 pm     Reply with quote

It may make sense if the LCD is remotely located from the main board
and you want to keep the cable size to a minimum. With i2c, it would
require only four wires: SCL, SDA, Vcc, Gnd.

Otherwise, it's 8 wires minimum.
temtronic



Joined: 01 Jul 2010
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PostPosted: Sun May 21, 2017 1:26 pm     Reply with quote

hmm... I can do it with just 2 wires, gnd and data....think of '1-wire' interface or the old MC14669 addressable UART of 3 decades ago...
bet not many heard or used that UART though.....

Jay
Ttelmah



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PostPosted: Sun May 21, 2017 2:13 pm     Reply with quote

What 'made sense' was PCM_programmer's comment about why the compile problem...

In fact there are I2C LCD's, or serial LCD's, so if it is just a matter of saving pins, much easier solutions.

The key though is that this is really about learning how to write code and compile it.
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