user11367: I bought a few PFC8574 and 4x4 keypads for a small project. I'm unclear on the correct wiring of the keypad to the PFC8574.
On the Arduino Playground's site, there are pull-up resistors for each column, but on a few other sites (like this one that I can't read, but I understand a schematic and there's a third example too, but I don't have the reputation to post it), the wiring does straight into the IC.
Does it depend on the library that's being used?  Or what am I missing?
Thanks!

user19520: Ok look at this image:

I'm not sure how your keypad is layed out but if you use a probe pin to test your connections via a multimeter, you can mark which ones correspond to the image.
I am ASSUMING you are going to use the code from arduino playground.
This is the format:
Pins of keypad (IN THE IMAGE) - Pins of PFC8547
Here are the pin connections:
1 - nothing
2 - 9
3 - 4
4 - 6
5 - 7
6 - 10
7 - 11
8 - 5
Also include the pull-up resistors.
Your ABCD keys will be ignored
(This is like wiring a bomb...)

11367: <p>I bought a few PFC8574 and 4x4 keypads for a small project. I'm unclear on the correct wiring of the keypad to the PFC8574.</p>

<p>On the <a href="http://playground.arduino.cc/Main/I2CPortExpanderAndKeypads" rel="nofollow noreferrer">Arduino Playground's site</a>, there are pull-up resistors for each column, but on a few other sites (like <a href="http://majsterkowo.pl/klawiatura-numeryczna-pod-i2c/" rel="nofollow noreferrer">this one</a> that I can't read, but I understand a schematic and there's a third example too, but I don't have the reputation to post it), the wiring does straight into the IC.</p>

<p>Does it depend on the library that's being used?  Or what am I missing?</p>

<p>Thanks!</p>
 19520: <p>Ok look at this image:
<a href="https://i.stack.imgur.com/BjyAG.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/BjyAG.jpg" alt="enter image description here"></a></p>

<p>I'm not sure how your keypad is layed out but if you use a probe pin to test your connections via a multimeter, you can mark which ones correspond to the image.</p>

<p>I am ASSUMING you are going to use the code from arduino playground.</p>

<p>This is the format:</p>

<p>Pins of keypad (<strong>IN THE IMAGE</strong>) - Pins of PFC8547</p>

<p>Here are the pin connections:</p>

<p>1 - nothing</p>

<p>2 - 9</p>

<p>3 - 4</p>

<p>4 - 6</p>

<p>5 - 7</p>

<p>6 - 10</p>

<p>7 - 11</p>

<p>8 - 5</p>

<p>Also include the pull-up resistors.
Your ABCD keys will be ignored</p>

<p>(This is like wiring a bomb...)</p>
