Filter example + README

example/4d-movement.c

@@ -75,7 +75,7 @@ int main() {
     lis.cfg.int1.latch = 1;
 
     /* set up a HP filter to ignore constant earth acceleration */
-    lis.cfg.filter.mode = LIS3DH_FILTER_MODE_NORMAL_REF;
+    lis.cfg.filter.mode = LIS3DH_FILTER_MODE_NORMAL;
     lis.cfg.filter.cutoff = LIS3DH_FILTER_CUTOFF_8;
     lis.cfg.filter.ia1 = 1; /* enable filter for INT1 generator */
 

example/4d-position.c

@@ -75,7 +75,7 @@ int main() {
     lis.cfg.int1.latch = 1;
 
     /* set up a HP filter to ignore constant earth acceleration */
-    lis.cfg.filter.mode = LIS3DH_FILTER_MODE_NORMAL_REF;
+    lis.cfg.filter.mode = LIS3DH_FILTER_MODE_NORMAL;
     lis.cfg.filter.cutoff = LIS3DH_FILTER_CUTOFF_8;
     lis.cfg.filter.ia1 = 1; /* enable filter for INT1 generator */
 

example/6d-movement.c

@@ -76,7 +76,7 @@ int main() {
     lis.cfg.int1.latch = 1;
 
     /* set up a HP filter to ignore constant earth acceleration */
-    lis.cfg.filter.mode = LIS3DH_FILTER_MODE_NORMAL_REF;
+    lis.cfg.filter.mode = LIS3DH_FILTER_MODE_NORMAL;
     lis.cfg.filter.cutoff = LIS3DH_FILTER_CUTOFF_8;
     lis.cfg.filter.ia1 = 1; /* enable filter for INT1 generator */
 

example/6d-position.c

@@ -76,7 +76,7 @@ int main() {
     lis.cfg.int1.latch = 1;
 
     /* set up a HP filter to ignore constant earth acceleration */
-    lis.cfg.filter.mode = LIS3DH_FILTER_MODE_NORMAL_REF;
+    lis.cfg.filter.mode = LIS3DH_FILTER_MODE_NORMAL;
     lis.cfg.filter.cutoff = LIS3DH_FILTER_CUTOFF_8;
     lis.cfg.filter.ia1 = 1; /* enable filter for INT1 generator */
 

example/README.md

@@ -1,5 +1,6 @@
 # lis3dh/example
 
+## Operating mode
 The LIS3DH has 3 operating modes.
 | mode | symbol | description |
 |------|---------|------------|
@@ -7,6 +8,7 @@ The LIS3DH has 3 operating modes.
 | Normal | `LIS3DH_MODE_NORMAL` | "Normal" mode. 10-bit acc. reading resolution. |
 | HR | `LIS3DH_MODE_HR` | High-resolution mode. 12-bit acc. reading resolution. |
 
+## ODR
 There are serveral `ODR` (internal data/sample rate) options, but some may only be used in a specific operating mode.
 | ODR | mode | symbol |
 |-----|------|--------|
@@ -21,6 +23,18 @@ There are serveral `ODR` (internal data/sample rate) options, but some may only
 | 1600 Hz | LP | `LIS3DH_ODR_LP_1600_HZ` |
 | 5376 Hz | LP | `LIS3DH_ODR_LP_5376_HZ` |
 
+## Filter
+The LIS3DH can apply its built-in high-pass filter to samples [regular reading, FIFO reading] and some specific user-functions. It has 3 different modes.
+| mode | symbol | description |
+|------|--------|-------------|
+| Normal | `LIS3DH_FILTER_MODE_NORMAL` | Use `lis3dh_reference()` to set the filter to the current accel field, without having to wait for it to settle at/near it. |
+| Autoreset | `LIS3DH_FILTER_MODE_AUTORESET` | Same as `normal` but this mode also automatically resets itself upon an interrupt(*). |
+| REFERENCE | `LIS3DH_FILTER_MODE_REFERENCE` | Output data is calculated as the difference between `cfg.reference` and the measured acceleration. |
+
+\* INT by the generator which the filter is programmed to apply itself to.
+
+See files: `filter-normal.c`, and `filter-reference.c`.
+
 ### file: simple.c
 Basic example of how to use this device
 

example/double-click.c

@@ -52,7 +52,7 @@ int main() {
     lis.cfg.range = LIS3DH_FS_2G;
     lis.cfg.rate = LIS3DH_ODR_400_HZ; /* minimum recommended ODR */
     
-    lis.cfg.filter.mode = LIS3DH_FILTER_MODE_NORMAL_REF;
+    lis.cfg.filter.mode = LIS3DH_FILTER_MODE_NORMAL;
     lis.cfg.filter.cutoff = LIS3DH_FILTER_CUTOFF_8;
     lis.cfg.filter.click = 1; /* enable filtering for CLICK function */
 

example/filter-normal.c

@@ -0,0 +1,63 @@
+#define _GNU_SOURCE
+#include <unistd.h> /* usleep() */
+#include <stdio.h>
+#include "lis3dh.h"
+#include "i2c.h"
+
+int main() {
+    
+    lis3dh_t lis;
+
+    lis.dev.init = i2c_init;
+    lis.dev.read = i2c_read;
+    lis.dev.write = i2c_write;
+    lis.dev.sleep = usleep;
+    lis.dev.deinit = i2c_deinit;
+
+    /* initialise LIS3DH struct */
+    if (lis3dh_init(&lis)) {
+        /* error handling */
+    }
+
+    /* reset device just in case */
+    if (lis3dh_reset(&lis)) {
+        /* error handling */
+    }
+
+    lis.cfg.mode = LIS3DH_MODE_HR;
+    lis.cfg.range = LIS3DH_FS_2G;
+    lis.cfg.rate = LIS3DH_ODR_100_HZ;
+
+    /* normal mode */
+    lis.cfg.filter.mode = LIS3DH_FILTER_MODE_NORMAL;
+    /* 3dB cutoff freq (~ ODR) */
+    lis.cfg.filter.cutoff = LIS3DH_FILTER_CUTOFF_8;
+
+    /* write config to device */
+    if (lis3dh_configure(&lis)) {
+        /* error handling */
+    }
+
+    /* read REFERENCE to set filter to current accel field */
+    if (lis3dh_reference(&lis)) {
+        /* error handling */
+    }
+
+    for ( ;; ) {
+
+        /* read an [x y z] accel set. Filter is applied */
+        if (lis3dh_read(&lis)) {
+            /* error handling */
+        }
+
+        printf("x: %4.d, y: %4.d, z: %4.d\n", lis.acc.x, lis.acc.y, lis.acc.z);
+        usleep(5000); /* 5 ms */
+    }
+
+    /* deinitalise struct */
+    if (lis3dh_deinit(&lis)) {
+        /* error handling */
+    }
+
+    return 0;
+}

example/filter-reference.c

@@ -0,0 +1,73 @@
+#define _GNU_SOURCE
+#include <unistd.h> /* usleep() */
+#include <stdio.h>
+#include "lis3dh.h"
+#include "i2c.h"
+
+int main() {
+    
+    lis3dh_t lis;
+
+    lis.dev.init = i2c_init;
+    lis.dev.read = i2c_read;
+    lis.dev.write = i2c_write;
+    lis.dev.sleep = usleep;
+    lis.dev.deinit = i2c_deinit;
+
+    /* initialise LIS3DH struct */
+    if (lis3dh_init(&lis)) {
+        /* error handling */
+    }
+
+    /* reset device just in case */
+    if (lis3dh_reset(&lis)) {
+        /* error handling */
+    }
+
+    lis.cfg.mode = LIS3DH_MODE_HR;
+    lis.cfg.range = LIS3DH_FS_2G;
+    lis.cfg.rate = LIS3DH_ODR_100_HZ;
+
+    /* normal mode */
+    lis.cfg.filter.mode = LIS3DH_FILTER_MODE_REFERENCE;
+    /* 3dB cutoff freq (~ ODR) */
+    lis.cfg.filter.cutoff = LIS3DH_FILTER_CUTOFF_8;
+
+    /* Output [x y z] data is calculated as the difference between the 
+    * measured acceleration and the value stored in REFERENCE.
+    * signed 7-bit int, 1 LSb value depends on FS.
+    * FS_2G: ~ 16mg per 1 LSb 
+    * FS_4G: ~ 31mg per 1 LSb 
+    * FS_8G: ~ 63mg per 1 LSb
+    * FS_16G: ~127mg per 1 LSb */
+    /* @ 2G,
+     * To have the output data be referenced to 0.8g:
+     * => 800 mg / 16 mg = 50 */
+    /* to reference -0.8g simply put -50 */
+    lis.cfg.reference = 50;
+
+    /* write config to device */
+    if (lis3dh_configure(&lis)) {
+        /* error handling */
+    }
+
+    /* Do not read REFERENCE */
+
+    for ( ;; ) {
+
+        /* read an [x y z] accel set. Filter is applied */
+        if (lis3dh_read(&lis)) {
+            /* error handling */
+        }
+
+        printf("x: %4.d, y: %4.d, z: %4.d\n", lis.acc.x, lis.acc.y, lis.acc.z);
+        usleep(5000); /* 5 ms */
+    }
+
+    /* deinitalise struct */
+    if (lis3dh_deinit(&lis)) {
+        /* error handling */
+    }
+
+    return 0;
+}

example/inertial-wakeup.c

@@ -76,7 +76,7 @@ int main() {
     lis.cfg.int1.latch = 1;
 
     /* set up a HP filter to ignore constant earth acceleration */
-    lis.cfg.filter.mode = LIS3DH_FILTER_MODE_NORMAL_REF;
+    lis.cfg.filter.mode = LIS3DH_FILTER_MODE_NORMAL;
     lis.cfg.filter.cutoff = LIS3DH_FILTER_CUTOFF_8;
     lis.cfg.filter.ia1 = 1; /* enable filter for INT1 generator */
     

example/single-click.c

@@ -39,7 +39,7 @@ int main() {
     lis.cfg.mode = LIS3DH_MODE_HR;
     lis.cfg.range = LIS3DH_FS_2G;
     lis.cfg.rate = LIS3DH_ODR_400_HZ; /* minimum recommended ODR */
-    lis.cfg.filter.mode = LIS3DH_FILTER_MODE_NORMAL_REF;
+    lis.cfg.filter.mode = LIS3DH_FILTER_MODE_NORMAL;
     lis.cfg.filter.cutoff = LIS3DH_FILTER_CUTOFF_8;
     lis.cfg.filter.click = 1; /* enable filtering for CLICK function */
 

lis3dh.h

@@ -36,6 +36,7 @@
 #define LIS3DH_STATUS_ZOR(c)      (!!(c & 0x40)) /* Z-axis data has overrun (been overwritten) */
 #define LIS3DH_STATUS_ZYXOR(c)    (!!(c & 0x80)) /* {Z,Y,X}-axis data has overrun (been overwritten) */
 
+
 /* rates */
 /* all power modes */
 #define LIS3DH_ODR_POWEROFF 0x00
@@ -52,17 +53,20 @@
 #define LIS3DH_ODR_LP_1600_HZ 0x08
 #define LIS3DH_ODR_LP_5376_HZ 0x09
 
+
 /* range/sens */
 #define LIS3DH_FS_2G  0x00 /* Full-scale sensing range: ± 2G */
 #define LIS3DH_FS_4G  0x01 /* Full-scale sensing range: ± 4G */
 #define LIS3DH_FS_8G  0x02 /* Full-scale sensing range: ± 8G */
 #define LIS3DH_FS_16G 0x03 /* Full-scale sensing range: ± 16G */
 
+
 /* operating modes */
 #define LIS3DH_MODE_HR     0x00 /* High resolution: 12-bit */
 #define LIS3DH_MODE_LP     0x01 /* Low-power: 8-bit */
 #define LIS3DH_MODE_NORMAL 0x02 /* Normal: 10-bit */
 
+
 /* FIFO modes */
 /* FIFO is not operational, and the buffer is reset. Must be used for switching FIFO modes */
 #define LIS3DH_FIFO_MODE_BYPASS         0x00
@@ -77,11 +81,7 @@
 #define LIS3DH_FIFO_TRIG_INT1 0x00
 #define LIS3DH_FIFO_TRIG_INT2 0x01
 
-/* filter modes */
-/* Normal mode
- * but reset by reading REFERENCE, instantly removes the DC component 
- */
-#define LIS3DH_FILTER_MODE_NORMAL_REF 0x00
+
 /* Reference mode
  * Output [x y z] data is calculated as the difference between the 
  * measured acceleration and the value stored in REFERENCE.
@@ -89,31 +89,31 @@
  * FS_2G: ~ 16mg per 1 LSb 
  * FS_4G: ~ 31mg per 1 LSb 
  * FS_8G: ~ 63mg per 1 LSb
- * FS_16G: ~127mg per 1 LSb
- * */
+ * FS_16G: ~127mg per 1 LSb */
 #define LIS3DH_FILTER_MODE_REFERENCE  0x01
+
 /* Normal mode
- * Probably the same as LIS3DH_FILTER_MODE_NORMAL_REF
- */
+ * Probably the same as 0x00 */
 #define LIS3DH_FILTER_MODE_NORMAL     0x02 
+
 /* Autoreset mode
  * The filter is automatically reset upon configured interrupt event.
- * It can be reset at any time by reading REFERENCE.
- */
+ * It can be reset at any time by reading REFERENCE. */
 #define LIS3DH_FILTER_MODE_AUTORESET  0x03
 
+
 /* filter cutoff */
 /* unfortunately, there is only a table for low-power mode,
-   and the actual cutoff-frequency depends on the ODR.
-   Naming scheme after ODR@400Hz
-   AN3308 > section 4.3.1.1 */
+ * and the actual cutoff-frequency depends on the ODR.
+ * Naming scheme after ODR@400Hz
+ * AN3308 > section 4.3.1.1 */
 #define LIS3DH_FILTER_CUTOFF_8 0x00 /* highest freq */
 #define LIS3DH_FILTER_CUTOFF_4 0x01
 #define LIS3DH_FILTER_CUTOFF_2 0x02
 #define LIS3DH_FILTER_CUTOFF_1 0x03 /* lowest freq */
 
-/* Note: IA{1,2} is interrupt activity {1,2} or interrupt generators */
 
+/* Note: IA{1,2} is interrupt activity {1,2} or interrupt generators */
 /* user provided functions, init and deinit can be set to NULL and won't be used */
 struct lis3dh_device {
     int (*init)(void);