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--- projects:i2c_pcf8574_8bit_port_expander [2012/10/21 17:50]
elger created
+++ projects:i2c_pcf8574_8bit_port_expander [2012/10/21 18:30]
elger
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 ===== The breadboard built =====
+The four resistors are 100Ω
+The four LEDs are regular red 3mm leds
+The four buttons are momentary on push buttons
+==== Fritzing ====
+{{ :projects:i2c_pcf8574_8bit_port_expander:pcf8574-arduino-io_bb.png?400|}}
+The program called [[http://fritzing.org/welcome/|Fritzing]] does a nice job of making an understandable picture of the board.
+This is not only nice for using in a write-up but in real-live it is faster than pulling everything from your breadboard just to place components a couple of holes further away (because you need the extra space).
+Fritzing can also make a schematic, I've included it here but it looks horrible. When I make the final design on a PCB I will use [[http://www.cadsoftusa.com/|Eagle]] for this.
+{{ :projects:i2c_pcf8574_8bit_port_expander:pcf8574-arduino-io_schem.png?200|}}
+==== Breadboard ====
+I took a photo of the breadboard build, nice to see but difficult to see where what goes:
+{{ :projects:i2c_pcf8574_8bit_port_expander:2012-10-21_11-36-11_88.jpg?200| }}
+{{ :projects:i2c_pcf8574_8bit_port_expander:2012-10-21_15-52-19_558.jpg?200| }}
+==== The code ====
+The [[http://www.arduino.cc/playground/Learning/Linux|Arduino IDE]] has a library called [[http://arduino.cc/en/Reference/Wire|Wire]] which is used for I2C stuff.
+I wrote code that reads the button input and writes this to the LED output:
+<file c PCF8574.ino>
+// I2C PCF8574 8 bit i/o port expander
+// by AEP
+//
+// testing / prototyping the Wire library in combination with the ic PCF8574
+// Reads data from PCF8574 over I2C and sends data to another PCF8574 over the same I2C bus
+// Created 21 oct 2012
+#include <Wire.h>
+byte iInput=0;
+byte iOutput=0;
+void setup()
+{
+  Wire.begin();
+}
+void loop()
+{
+  Wire.requestFrom(33,1);// Begin transmission to PCF8574 with the buttons
+  if(Wire.available())   // If bytes are available to be recieved
+  {
+    iInput = Wire.read();// Read a byte
+  }
+  if(iInput<255)         //If the value less than 255
+  {
+    if (iInput==254) // P0
+    {
+      iOutput = 1;
+    };
+    if (iInput==253) // P1
+    {
+      iOutput = 2;
+    };
+    if (iInput==251) // P2
+    {
+      iOutput = 4;
+    };
+    if (iInput==247) // P3
+    {
+      iOutput = 8;
+    };
+  }
+  Wire.beginTransmission(32);  //Begin transmission to PCF8574 (with the LEDs)
+  Wire.write(iOutput);         //Send data to PCF8574 (with the LEDs)
+  Wire.endTransmission();      //End Transmission to PCF8574 (with the LEDs)
+}
+</file>