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projects:i2c_pcf8574_8bit_port_expander [2012/10/21 18:29] elger |
projects:i2c_pcf8574_8bit_port_expander [2016/11/16 13:06] |
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| - | ====== I2C pcf8574 8bit port expander ====== | ||
| - | I made a test / prototype setup on a breadboard with two pcf8574 ics ; one for output and one for input. Both connected to the same I2C bus. | ||
| - | Adding more digital inputs to an Arduino was my first objective, as I am planning to use this on a project which has buttons that control a menu. | ||
| - | |||
| - | For now this little write-up should suffice for the moment I am going to design a PCB for this. | ||
| - | |||
| - | ===== 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 | ||
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| - | #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> | ||