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Filter example + README

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William Clark 2024-01-07 18:11:24 +00:00
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example/README.md
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# 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

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example/filter-normal.c Normal file
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#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;
}

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example/filter-reference.c Normal file
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#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;
}