Revision 0:db4e3d0374fe, committed 2012-10-31

Comitter:

DaveStyles

Date:

Wed Oct 31 21:43:28 2012 +0000

Commit message:

MCP3221 12Bit I2C ADC Library

Changed in this revision

diff -r 000000000000 -r db4e3d0374fe MCP3221.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/MCP3221.cpp	Wed Oct 31 21:43:28 2012 +0000
@@ -0,0 +1,50 @@
+
+#include "MCP3221.h"
+
+//Create instance
+MCP3221::MCP3221(PinName sda, PinName scl, float supplyVoltage) : i2c(sda, scl), _supplyVoltage(supplyVoltage)
+{
+}
+
+//destroy instance
+MCP3221::~MCP3221()
+{
+}
+
+float MCP3221::read()
+{
+
+//You cannot write to an MCP3221, it has no writable registers.
+//MCP3221 also requires an ACKnowledge between each byte sent, before it will send the next byte. So we need to be a bit manual with how we talk to it.
+//It also needs an (NOT) ACKnowledge after the second byte or it will keep sending bytes (continuous sampling)
+//
+//From the datasheet.
+//
+//I2C.START
+//Send 8 bit device/ part address to open conversation.   (See .h file for part explanation)
+//read a byte (with ACK)
+//read a byte (with NAK)
+//I2C.STOP
+
+
+  //  char data[2];
+
+    i2c.start();
+    int acknowledged = i2c.write(MCP3221_CONVERSE); //send a byte to start the conversation. It should be acknowledged.
+    _data[0] = i2c.read(1);  //read a byte. acknowledge when we have it.
+    _data[1] = i2c.read(0);  //read the second byte. (n)acknowledge when we have it to stop the flow.
+    i2c.stop();
+ 
+    //convert to 12 bit.
+    short res;
+    int _12_bit_var; // 2 bytes
+    char _4_bit_MSnibble = _data[0]; // 1 byte, example 0000 1000
+    char _8_bit_LSByte = _data[1];   // 1 byte, example 1111 0000
+
+    _12_bit_var = ((0x0F & _4_bit_MSnibble) << 8) | _8_bit_LSByte;   //example 100011110000
+    res=_12_bit_var;
+
+    return  (_supplyVoltage/4096) * res;
+
+}
+

diff -r 000000000000 -r db4e3d0374fe MCP3221.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/MCP3221.h	Wed Oct 31 21:43:28 2012 +0000
@@ -0,0 +1,93 @@
+/*
+
+* ***** NOTE ***** **************************************************** *
+* THIS LIBRARY IS FOR AN MCP3221A5T-I/OT - WHICH HAS AN ADDRESS OF  101 *
+* ***** **** ***** **************************************************** *
+
+ * Copyright (c) 2012 dstyles, MIT License
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of this software 
+ * and associated documentation files (the "Software"), to deal in the Software without restriction, 
+ * including without limitation the rights to use, copy, modify, merge, publish, distribute, 
+ * sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is 
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all copies or 
+ * substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING 
+ * BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND 
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, 
+ * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+ 
+/* Datasheet Information:
+*
+* The address byte is the first byte received following the
+* START condition from the master device. The first part
+* of the control byte consists of a 4-bit device code,
+* which is set to 1001 for the MCP3221. The device code
+* is followed by three address bits: A2, A1 and A0. The
+* default address bits are 101. Contact the Microchip
+* factory for additional address bit options. The address
+* bits allow up to eight MCP3221 devices on the same
+* bus and are used to determine which device is
+* accessed.
+*
+* The eighth bit of the slave address determines if the
+* master device wants to read conversion data or write to
+* the MCP3221. When set to a ‘1’, a read operation is
+* selected. When set to a ‘0’, a write operation is
+* selected. There are no writable registers on the
+* MCP3221. Therefore, this bit must be set to a ’1’ in
+* order to initiate a conversion.
+*
+* ***** NOTE ***** *****************************************************************************************
+* THIS LIBRARY IS FOR AN MCP3221A5T-I/OT - WHICH HAS AN ADDRESS OF  101  - The A5 bit denotes the address
+* ***** **** ***** *****************************************************************************************
+*/
+
+
+#ifndef MCP3221_H
+
+#define MCP3221_H
+
+#include "mbed.h"
+
+#define    MCP3221_CONVERSE 0x9B //10011011 NOTE IT ENDS IN 1, this is the READ ADDRESS. This is all this device does.
+                                 //It opens a conversation via this specific READ address
+
+//Library for the MCP3221 12 BIT ADC.
+
+class MCP3221
+{
+public:
+
+  /*
+  Creates instance
+  Connect module using I2C port pins sda and scl. The output is referenced to the supply voltage which can be
+  2.7v to 5.0v. The read will return the correct voltage, if you supply the correct supplyVoltage when instantiating.
+  */
+  MCP3221(PinName sda, PinName scl, float supplyVoltage);
+  
+  /*
+  Destroys instance.
+  */ 
+  ~MCP3221();
+  
+  /*
+  Reads the analog register of the MCP3221 and converts it to a useable value. (a voltage) 
+  */
+  float read();
+  
+private:
+  
+  I2C i2c;
+  float _supplyVoltage;
+  char _data[2];
+
+};
+
+#endif
+