Revision 0:778d41341161, committed 2016-11-09

Comitter:

ChrisMabey

Date:

Wed Nov 09 17:40:41 2016 +0000

Commit message:

Example of how to use the LTC1865 2-Channel SPI 16-bit ADC.

Changed in this revision

diff -r 000000000000 -r 778d41341161 main.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main.cpp	Wed Nov 09 17:40:41 2016 +0000
@@ -0,0 +1,153 @@
+/***************************************************************************************/
+/*                                                                                     */
+/* Program:         LTC1865_ADC_Example                                                */
+/* Author:          Chris Mabey                                                        */
+/* Date:            November 2016                                                      */
+/* Target Platform: mbed                                                               */
+/* Description:     External LTC1865 16-bit ADC example                                */
+/* Version:         1v0                                                                */
+/*                                                                                     */
+/* Notes: After struggling with the internal LPC1768 ADC noise I decided to use an     */
+/*        external ADC. My requirements were 2 channels at 16-bit resolution, single   */
+/*        5V supply, input range 0 to 5V (Vcc), high sample rate and using a fast SPI  */
+/*        clock frequency.                                                             */
+/*        I'm very happy with the LTC1855 and as I've received help from the mbed      */
+/*        community thought I'd share an example that may be of help to others.        */
+/*                                                                                     */
+/*        LTC1865 Datasheet: http://cds.linear.com/docs/en/datasheet/18645fb.pdf       */
+/*                                                                                     */
+/*        Please don't criticise my coding style, it's 'old school' from when I worked */
+/*        with Intel iRMX and the PL/M language 30 or so years ago!                    */
+/*                                                                                     */
+/***************************************************************************************/
+
+#include "mbed.h"
+
+/* ADC (SPI) */
+/* ========= */
+#define SPI_MOSI_PIN      p5  /* SPI Bus Master Out/Slave In          */
+#define SPI_MISO_PIN      p6  /* SPI Bus Master In/Slave Out          */
+#define SPI_SCK_PIN       p7  /* SPI Bus Master Clock                 */
+#define SPI_CS_ADC_PIN    p8  /* SPI ADC Slave Select                 */
+
+/* The LTC1864 ADC has two input channels */
+#define ADC_CHANNEL_0 0
+#define ADC_CHANNEL_1 1
+
+/* The LTC1864 conversion cycle begins with the rising edge of CONV.  */
+/* After a period equal to tCONV, the conversion is finished.         */
+/* The maximum conversion time is 3.2uS, so wait for 4uS as wait_us() */
+/* accepts an integer value.                                          */ 
+#define ADC_CONVERSION_TIME 4
+
+#define LOW  0
+#define HIGH 1
+
+
+/**********************************************************/
+/*                                                        */
+/* MBED I/O Ports                                         */
+/*                                                        */
+/**********************************************************/
+DigitalOut ADCcsPin(SPI_CS_ADC_PIN);
+SPI spi(SPI_MOSI_PIN, SPI_MISO_PIN, SPI_SCK_PIN);
+
+
+/* Holds the last ADC conversion channel */
+unsigned char previousADCchannel;
+
+
+/***********************************************************/
+/*                                                         */
+/* Read_External_ADC                                       */
+/*                                                         */
+/* Function: Read the latest value from the specified      */
+/*           channel of the external LTC1865 ADC.          */
+/*                                                         */
+/*           Performance: Takes around 15.5uS to execute   */
+/*           using 20MHz SPI clock without dummy read for  */
+/*           switching channels (measured on NUCLEO-L476RG)*/
+/*                                                         */
+/* Input Parameters:                                       */
+/* unsigned char: the ADC channel (ADC_LP_CHANNEL or       */
+/*                ADC_GP_CHANNEL)                          */
+/*                                                         */
+/* Output Parameters:                                      */
+/* unsigned int: the ADC value (range 0 to 65535)          */
+/*                                                         */
+/***********************************************************/
+unsigned int Read_External_ADC(unsigned char channel)
+{
+    unsigned int adcVal;
+
+    /* If changing channel a dummy read is required as the */
+    /* two bits of the input word (SDI) assign the MUX     */
+    /* configuration for the next requested conversion.    */
+    /*                       ----                          */
+    if (channel != previousADCchannel)
+    {  
+        /* The LTC1865 conversion cycle begins with the rising edge of CONV */
+        ADCcsPin = HIGH;
+
+        /* Wait for the conversion to complete */
+        wait_us(ADC_CONVERSION_TIME); /* Note: Blocks interrupts! */
+
+        /* Enable the Serial Data Out to allow the data to be shifted out by taking CONV low */
+        ADCcsPin = LOW;
+        
+        /* Send command and read previous selected ADC channel value, whilst */
+        /* telling the ADC the next conversion is for the new channel        */
+        adcVal = spi.write(0x8000 | (((unsigned int)channel) << 14)); /* Transmit the Mode (Single-ended MUX Mode),     */
+                                                                      /* the channel and receive the sixteen bit result */
+    
+        /* Save the new ADC channel */
+        previousADCchannel = channel;        
+    }
+    /* endif */
+
+    /* The LTC1865 conversion cycle begins with the rising edge of CONV */
+    ADCcsPin = HIGH;
+
+    /* Wait for the conversion to complete */
+    wait_us(ADC_CONVERSION_TIME);
+
+    /* Enable the Serial Data Out to allow the data to be shifted out by taking CONV low */
+    ADCcsPin = LOW;
+
+    /* Send command and read previous selected ADC channel value, whilst */        
+    /* telling the ADC the next conversion is for the same channel       */
+    adcVal = spi.write(0x8000 | (((unsigned int)channel) << 14)); /* Transmit the Mode (Single-ended MUX Mode),     */
+                                                                  /* the channel and receive the sixteen bit result */
+
+    return(adcVal);  /* Return the 16-bit ADC value */
+}
+
+
+int main()
+{
+    /**********************************************************/
+    /*                                                        */
+    /* Initialise the SPI interface to the external ADC       */
+    /*                                                        */
+    /**********************************************************/
+    spi.format(16,1);        /* 16-bit data, Mode 1 */
+    spi.frequency(20000000); /* 20MHz clock rate    */
+
+    ADCcsPin = LOW; /* Deselect the ADC by setting chip select low */
+
+    /* Perform a dummy read to initialise the ADC conversion channel to ADC_CHANNEL_0 */
+    Read_External_ADC(ADC_CHANNEL_0);
+
+    printf("\n\rLTC1865 External ADC Example\n\r");
+
+    while(1)
+    {
+        printf("Channel 0 = %5u   ", Read_External_ADC(ADC_CHANNEL_0));
+
+        wait(0.5f); /* 0.5s */
+
+        printf("Channel 1 = %5u\n\r", Read_External_ADC(ADC_CHANNEL_1));        
+    }
+    /* end while */
+}
+

diff -r 000000000000 -r 778d41341161 mbed.bld
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mbed.bld	Wed Nov 09 17:40:41 2016 +0000
@@ -0,0 +1,1 @@
+http://mbed.org/users/mbed_official/code/mbed/builds/0ab6a29f35bf
\ No newline at end of file