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ADXL345: Interrupts work on SPI but not I2C

Posted: Mon Apr 29, 2019 2:44 pm
by borkborkbork
Has anyone been able to get interrupts to work with I2C mode? They work fine with the example code when using a SPI interface.

Here's what I have debugged:

1. Start with the example sketch from SparkFun ( the one that by default as the ADXL_ISR in the loop() rather than as an interrupt)
2. Compile for SPI (CS=10) and do not attach the interrupt; wire breadboard to communicate via SPI
3. As coded, the ADXL_ISR is called from loop() so I see the correct interrupt messages (tap, double tap, etc.)
4. Recompile for I2C and put the breakout into a different region of the breadboard wired for I2C power at 3.3V with pullups (note I'm using an Arduino Pro Mini at 3.3V so there is no need for level shifting; note I had to wire in pins for A4/A5 that are in the middle of the board and not on a the standard DIP layout)
5. Everything works fine as in step #3

Yay! everything works fine in polling mode.

Now do this:

1. Move device back to breadboard area for SPI
3. Connect ADXL pin for INT1 to Pro/Mini D2
4. Attach the ADXL_ISR to digital pin 2 by uncommenting out the code; comment out loop() call to ADXL_ISR.
5. Compile in SPI mode

Yay! Everything works! The ISR is printing out the interrupts as expected without polling via loop().

Now here's the problem:

1. Move the device back to the I2C breadboard region
2. Compile for I2C, leaving interrupt code intact
3. Open the monitor and ... hmmm .... does not work. Nothing happens when tapping it... I don't even see the inactivity interrupt , which worked fine in all 3 cases above.

There doesn't appear to be anything in the notes or datasheet that indicate special treatment of interrupts when I2C is enabled.

Did I miss something obvious?

Re: ADXL345: Interrupts work on SPI but not I2C

Posted: Mon May 06, 2019 10:23 am
by TS-Mark
Hi borkborkbork,

Sorry for the late reply. We are pretty sure this is an issue with the code and how it handles switching between I2C and SPI. Can you post your modified version of that example so we can verify the issue?

Re: ADXL345: Interrupts work on SPI but not I2C

Posted: Sat May 11, 2019 10:16 am
by borkborkbork
Hi TS-Mark,
I used the 101-level example code linked on the product page. Simply enable interrupts, then switch between SPI & I2C and in I2C mode the interrupt doesn't work ... I also used the default SparkFun lib, I can post that if you need it but... it's your code!? ;-)

Thanks for investigating!

Edited by moderator to add code tags
Code: Select all
/*  ********************************************* 
 *  SparkFun_ADXL345_Example
 *  Triple Axis Accelerometer Breakout - ADXL345 
 *  Hook Up Guide Example 
 *  Utilizing Sparkfun's ADXL345 Library
 *  Bildr ADXL345 source file modified to support 
 *  both I2C and SPI Communication
 *  E.Robert @ SparkFun Electronics
 *  Created: Jul 13, 2016
 *  Updated: Sep 06, 2016
 *  Development Environment Specifics:
 *  Arduino 1.6.11
 *  Hardware Specifications:
 *  SparkFun ADXL345
 *  Arduino Uno
 *  *********************************************/

#include <SparkFun_ADXL345.h>         // SparkFun ADXL345 Library

/*********** COMMUNICATION SELECTION ***********/
/*    Comment Out The One You Are Not Using    */
ADXL345 adxl = ADXL345(10);           // USE FOR SPI COMMUNICATION, ADXL345(CS_PIN);
//ADXL345 adxl = ADXL345();             // USE FOR I2C COMMUNICATION

/****************** INTERRUPT ******************/
/*      Uncomment If Attaching Interrupt       */
//int interruptPin = 2;                 // Setup pin 2 to be the interrupt pin (for most Arduino Boards)

/******************** SETUP ********************/
/*          Configure ADXL345 Settings         */
void setup(){
  Serial.begin(9600);                 // Start the serial terminal
  Serial.println("SparkFun ADXL345 Accelerometer Hook Up Guide Example");
  adxl.powerOn();                     // Power on the ADXL345

  adxl.setRangeSetting(16);           // Give the range settings
                                      // Accepted values are 2g, 4g, 8g or 16g
                                      // Higher Values = Wider Measurement Range
                                      // Lower Values = Greater Sensitivity

  adxl.setSpiBit(0);                  // Configure the device to be in 4 wire SPI mode when set to '0' or 3 wire SPI mode when set to 1
                                      // Default: Set to 1
                                      // SPI pins on the ATMega328: 11, 12 and 13 as reference in SPI Library 
  adxl.setActivityXYZ(1, 0, 0);       // Set to activate movement detection in the axes "adxl.setActivityXYZ(X, Y, Z);" (1 == ON, 0 == OFF)
  adxl.setActivityThreshold(75);      // 62.5mg per increment   // Set activity   // Inactivity thresholds (0-255)
  adxl.setInactivityXYZ(1, 0, 0);     // Set to detect inactivity in all the axes "adxl.setInactivityXYZ(X, Y, Z);" (1 == ON, 0 == OFF)
  adxl.setInactivityThreshold(75);    // 62.5mg per increment   // Set inactivity // Inactivity thresholds (0-255)
  adxl.setTimeInactivity(10);         // How many seconds of no activity is inactive?

  adxl.setTapDetectionOnXYZ(0, 0, 1); // Detect taps in the directions turned ON "adxl.setTapDetectionOnX(X, Y, Z);" (1 == ON, 0 == OFF)
  // Set values for what is considered a TAP and what is a DOUBLE TAP (0-255)
  adxl.setTapThreshold(50);           // 62.5 mg per increment
  adxl.setTapDuration(15);            // 625 μs per increment
  adxl.setDoubleTapLatency(80);       // 1.25 ms per increment
  adxl.setDoubleTapWindow(200);       // 1.25 ms per increment
  // Set values for what is considered FREE FALL (0-255)
  adxl.setFreeFallThreshold(7);       // (5 - 9) recommended - 62.5mg per increment
  adxl.setFreeFallDuration(30);       // (20 - 70) recommended - 5ms per increment
  // Setting all interupts to take place on INT1 pin
  //adxl.setImportantInterruptMapping(1, 1, 1, 1, 1);     // Sets "adxl.setEveryInterruptMapping(single tap, double tap, free fall, activity, inactivity);" 
                                                        // Accepts only 1 or 2 values for pins INT1 and INT2. This chooses the pin on the ADXL345 to use for Interrupts.
                                                        // This library may have a problem using INT2 pin. Default to INT1 pin.
  // Turn on Interrupts for each mode (1 == ON, 0 == OFF)
//attachInterrupt(digitalPinToInterrupt(interruptPin), ADXL_ISR, RISING);   // Attach Interrupt


/****************** MAIN CODE ******************/
/*     Accelerometer Readings and Interrupt    */
void loop(){
  // Accelerometer Readings
  int x,y,z;   
  adxl.readAccel(&x, &y, &z);         // Read the accelerometer values and store them in variables declared above x,y,z

  // Output Results to Serial
  //Serial.print(", ");
  //Serial.print(", ");
  // You may also choose to avoid using interrupts and simply run the functions within ADXL_ISR(); 
  //  and place it within the loop instead.  
  // This may come in handy when it doesn't matter when the action occurs. 


/********************* ISR *********************/
/* Look for Interrupts and Triggered Action    */
void ADXL_ISR() {
  // getInterruptSource clears all triggered actions after returning value
  // Do not call again until you need to recheck for triggered actions
  byte interrupts = adxl.getInterruptSource();
  // Free Fall Detection
  if(adxl.triggered(interrupts, ADXL345_FREE_FALL)){
    Serial.println("*** FREE FALL ***");
    //add code here to do when free fall is sensed
  // Inactivity
  if(adxl.triggered(interrupts, ADXL345_INACTIVITY)){
    Serial.println("*** INACTIVITY ***");
     //add code here to do when inactivity is sensed
  // Activity
  if(adxl.triggered(interrupts, ADXL345_ACTIVITY)){
    Serial.println("*** ACTIVITY ***"); 
     //add code here to do when activity is sensed
  // Double Tap Detection
  if(adxl.triggered(interrupts, ADXL345_DOUBLE_TAP)){
    Serial.println("*** DOUBLE TAP ***");
     //add code here to do when a 2X tap is sensed
  // Tap Detection
  if(adxl.triggered(interrupts, ADXL345_SINGLE_TAP)){
    Serial.println("*** TAP ***");
     //add code here to do when a tap is sensed

Re: ADXL345: Interrupts work on SPI but not I2C

Posted: Sun Jun 02, 2019 11:44 am
by borkborkbork
FYI this is on a 3.3V pro min 328 from sparkfun:

I had to solder on the I2C 4/5 headers in the middle of the board.

Re: ADXL345: Interrupts work on SPI but not I2C

Posted: Tue Sep 17, 2019 7:37 am
by uzer123
i have the same problem...spi and i2c works fine..but interrupt doesnt work at all...
did you find any solution?