Sensors: Introduction

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# 181U Spring 2020
### Sensors

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- Geoffrey Brown, 2020
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# Agenda

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* Types of Sensors
  - examples from hobby vendors
* Characteristics
  - communication interface, etc.
* Digging Down
* Software Model
* Drivers

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# Types of Sensors

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* Environmental
   - Temperature: **ambient**, infrared
   - **Humidity**
   - **Pressure**
   - Light
   - Proximity
   - Touch
   - Alcohol/Gas
* Position
   - **Magnetometer**
   - GPS
   - Distance
* Inertial
   - **Accelerometer**
   - **Gyroscope**

* Audio/Image
   - Camera
   - Microphone
* Mechanical
   - Strain
   - Weight
   - Compression
   - Flex
   - Vibration
* Electrical
   - magnetic
   - current
* Medical
   - heart (rate,ekg)
   - blood flow

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# Lab Board -- ST X-NUCLEO-IKS01A3
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![](images/space.png# w-10pct)
![](images/st-sensor-board.png# w-80pct)

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# Devices on ST X-NUCLEO-IKS01A3
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This board is designed to allow evaluation of a collection of sensors.  This is a typical offering of sensor manufacturers and makes system prototyping easy because
there is no need to build hardware to start the software development effort.

* [LSM6DSO:](https://www.st.com/en/mems-and-sensors/lsm6dso.html) MEMS 3D accelerometer (±2/±4/±8/±16 g) + 3D gyroscope (±125/±250/±500/±1000/±2000 dps)
* [LIS2MDL:](https://www.st.com/en/mems-and-sensors/lis2mdl.html) MEMS 3D magnetometer (±50 gauss)
* [LIS2DW12:](https://www.st.com/en/mems-and-sensors/lis2dw12.html) MEMS 3D accelerometer (±2/±4/±8/±16 g)
* [LPS22HH:](https://www.st.com/en/mems-and-sensors/lps22hh.html) MEMS pressure sensor, 260-1260 hPa absolute digital output barometer
* [HTS221:](https://www.st.com/en/mems-and-sensors/hts221.html) capacitive digital relative humidity and temperature
* [STTS751:](https://www.st.com/en/mems-and-sensors/stts751.html) Temperature sensor (–40 °C to +125 °C)
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# LPS22HH Pressure sensor
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![](images/space.png# w-10pct)
![](images/lps22h-pressure.png# w-40pct)
![](images/space.png# w-10pct)
![](images/steval-lps22hh.png# w-20pct)

[datasheet](https://www.st.com/resource/en/datasheet/lps22hh.pdf)

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# Easily Available Development Boards
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![https://www.sparkfun.com/categories/23?sort_by=name&per_page=200](images/sparkfunscreen.png# w-40pct)[link](https://www.sparkfun.com/categories/23?sort_by=name&per_page=200)
![](images/adafruit-sensors.png# w-40pct)[link](https://learn.adafruit.com/category/sensors)

* There are a number of vendors selling small "breakout boards" for prototyping
    - Sparkfun
    - Adafruit
* Also, manufacturers produce breakout boards available from
    - Digikey
    - Mouser

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# While Devices are Diverse, Interface "Model" isn't
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* Small number of hardware *interfaces* -- subject of next lecture
    - Serial
    - I2C  (used for lab device)
    - SPI
    - Analog (data delivered as voltage)
* Programmer model
    - Device is configured/read through a set of "registers" -- typical byte-wide
    - Most devices have separate interrupt signal
    - Some devices have programmable autonomous behavior (e.g. monitor for interesting "events")
* Low-level details are described in datasheet, often badly written
* Low-level programming issues
    - Configuration (typically a lot of options)
    - Data/configuration spread across multiple registers at bit level
    - Calibration (many sensors have calibration procedure/values)

* Low-level Drivers
    - Often provided by manufacturer of component
    - Abstract low-level details involving specific register r/w/bit-manipulation
    - Handle initialization, calibration
    - "Procedure" level interface (e.g. **float get_temperature()**)
* High-level Drivers
    - Integrate device into RTOS/operating system
    - Handle sharing of interface among threads
    - Handle interrupts, DMA for data transfers, etc
    - May provide data *stream* for signals sampled at regular frequency

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# Hardware Interfaces of Lab Devices

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| Device | Type | UART | SPI | I2C | Interrupt | Stream | Event Monitor |
|--------|------|:----:|:---:|:---:|:---------:|:--------------:|---------------|
| LSM6DSO | Accelerometer/Gyrosope |  |  ✔ | ✔ | ✔ | ✔ | step, tilt, significant motion, tap |
| LIS2MDL | Magnetometer           |  |  ✔ | ✔ | ✔ |   | significant change |
| LIS2DW12 | Accelerometer         |  |  ✔ | ✔ | ✔ | ✔ | stationary, motion, orientation, tap |
| LPS22HH | Pressure               |  |  ✔ | ✔ | ✔ | ✔ | threshold |
| HTS221 | Temperature/Humidity    |  |  ✔ | ✔ | |  | |
| STTS751 | Temperature            |  |    | ✔ | ✔ |  | high/low temperature limits |

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# STTS751 Temperature Sensor

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![](images/space.png# w-3-12th)
![](images/stts751-block-diagram.png# w-50pct)

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# HTS221 Temperature/Humidity Sensor

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![](images/space.png# w-20pct)
![](images/hts221-block-diagram.png# w-60pct)

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# LIS2DW12 Accelerometer
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![](images/space.png# w-3-12th)
![](images/lis2dw12-block-diagram.png# w-50pct)

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# LPS22HH Pressure :  Includes Signal Processing

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![](images/lps22h-block-diagram.png# w-50pct)

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# LSM6DSO Accel/gyro : Complex Processing

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![](images/lsm6dso-accel-filter.png# w-40pct fr)

![](images/lsm6dso-fsm.png# w-50pct)
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# Digging Down -- [HTS221](https://www.st.com/resource/en/datasheet/hts221.pdf)

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![](images/hts221-datasheet.png# w-40pct fr)

Device Data Sheet Defines
* Behavior
* Electrical Properties
* Sensor Specifications
* Registers
  - Bit level definitions
  - Operation sequences
  - Configuration options

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# HTS221 Specifications

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![](images/space.png# w-3-12th)
![](images/hts221-specifications.png# w-40pct)

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# HTS221 Register Map

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![](images/hts221-registers.png# w-50pct fr)

* WHO_AM_I :  Device identifier
* AV_CONF  :  Resolution Mode Configuration
* CONTROL_REGISTERS : power down, reboot, 
* CTRL_REG2 : Control Register (e.g reboot)
* STATUS_REG : Status (e.g. data available)
* HUMIDITY_OUT : Humidity data
* TEMP_OUT : Temperature data
* Calibration registers : part specfic calibration constants for temperature and humidity

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# HTS221 Register Examples

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![](images/hts221-status-reg.png# w-40pct)
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![](images/hts221-temp-out.png# w-40pct)

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# HTS221 Calibration Example 
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![](images/space.png# w-3-12th)
![](images/hts221-calibration.png# w-40pct)

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# HTS221 Low-level Driver (Example)
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![](images/hts221-status-reg.png# w-40pct fr)
```C
#define HTS221_STATUS_REG          0x27U
typedef struct {
  uint8_t t_da                 : 1;
  uint8_t h_da                 : 1;
  uint8_t not_used_01          : 6;
} hts221_status_reg_t;
...

int32_t hts221_status_get(stmdev_ctx_t *ctx, hts221_status_reg_t *val);
int32_t hts221_temp_data_ready_get(stmdev_ctx_t *ctx, uint8_t *val);
int32_t hts221_hum_data_ready_get(stmdev_ctx_t *ctx, uint8_t *val);
int32_t hts221_humidity_raw_get(stmdev_ctx_t *ctx, uint8_t *buff);
int32_t hts221_temperature_raw_get(stmdev_ctx_t *ctx, uint8_t *buff);
...
```
Low-level drivers simply provide a convenient interface to reading/writing registers by providing accessor functions to defined bit fields.

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# HTS221 Low-level Driver (Configuration)

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```C
 /* Read humidity calibration coefficient */
  axis1bit16_t coeff;
  lin_t lin_hum;
  hts221_hum_adc_point_0_get(&dev_ctx, &lin_hum.x0);
  hts221_hum_rh_point_0_get(&dev_ctx, &lin_hum.y0);
  hts221_hum_adc_point_1_get(&dev_ctx, &lin_hum.x1);
  hts221_hum_rh_point_1_get(&dev_ctx, &lin_hum.y1);

/* Read temperature calibration coefficient */
  lin_t lin_temp;
  hts221_temp_adc_point_0_get(&dev_ctx, &lin_temp.x0);
  hts221_temp_deg_point_0_get(&dev_ctx, &lin_temp.y0);
  hts221_temp_adc_point_1_get(&dev_ctx, &lin_temp.x1);
  hts221_temp_deg_point_1_get(&dev_ctx, &lin_temp.y1);

/* Enable Block Data Update */
  hts221_block_data_update_set(&dev_ctx, PROPERTY_ENABLE);
  /* Set Output Data Rate */
  hts221_data_rate_set(&dev_ctx, HTS221_ODR_1Hz);
  /* Device power on */
  hts221_power_on_set(&dev_ctx, PROPERTY_ENABLE);
  ```

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# HTS221 Low-level Driver (Reading data)

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Data reading
* Read status
* Read raw data
* Convert raw data to a measurement
<br>
<br>

```C
 while(1) {
    hts221_reg_t reg;
    hts221_status_get(&dev_ctx, &reg.status_reg);

if (reg.status_reg.h_da) { /* Read humidity data */
      hts221_humidity_raw_get(&dev_ctx, data_raw_humidity.u8bit);
      humidity_perc = linear_interpolation(&lin_hum, data_raw_humidity.i16bit);
    }
    if (reg.status_reg.t_da) {  /* Read temperature data */
      hts221_temperature_raw_get(&dev_ctx, data_raw_temperature.u8bit);
      temperature_degC = linear_interpolation(&lin_temp, data_raw_temperature.i16bit);
    }
    ...
```

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# HTS221 High(er)-level Driver

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ChibiOS driver provides an abstaction layer supporting multiple types of hydrometer,thermometer, etc.

![](images/chibios-hydrometer.png# w-40pct, fr)

```C
/**
 * @brief   Retrieves cooked data from the BaseHygrometer.
 ...
 *
 * @param[in] devp      pointer to @p HTS221Driver.
 * @param[out] axes     a buffer which would be filled with cooked data.
 *
 * @return              The operation status.
 * @retval MSG_OK       if the function succeeded.
 * @retval MSG_RESET    if one or more I2C errors occurred, the errors can
 *                      be retrieved using @p i2cGetErrors().
 * @retval MSG_TIMEOUT  if a timeout occurred before operation end.
 *
 * @api
 */
#define hts221HygrometerReadCooked(devp, axes)                              \
        hygrometerReadCooked(&((devp)->hygro_if), axes)
```

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# HTS221 High(er)-level Driver

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ChibiOS Driver provides:
* A portable interface
* Encapsulation of low-level details
* Intialization handles capturing calibration data and computing `m*x + b`

```C
static msg_t hygro_read_cooked(void *ip, float axes[]) {
  HTS221Driver* devp;
  int32_t raw;
  msg_t msg;

/* Getting parent instance pointer.*/
  devp = objGetInstance(HTS221Driver*, (BaseHygrometer*)ip);
  msg = hygro_read_raw(ip, &raw);
  *axes = (raw * devp->hygrosensitivity) - devp->hygrobias;

return msg;
}
```
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# HTS221 High(er)-level Driver

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```C
  hts221ObjectInit(&HTS221D1);  /* HTS221 Object Initialization.*/
  hts221Start(&HTS221D1, &hts221cfg); /* Activates the HTS221 driver.*/
  while (true) {
    hts221HygrometerReadCooked(&HTS221D1, &hygrocooked);
    hts221ThermometerReadCooked(&HTS221D1, &thermocooked);
    ...
  }
}
```
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# Summary

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* Sensors
  - types
  - software model
  - drivers

* Cover image: By Tosaka - 　<a href="//commons.wikimedia.org/wiki/Special:BookSources/4534040083" title="Special:BookSources/4534040083">ISBN 4534040083</a>), <a href="https://creativecommons.org/licenses/by/3.0" title="Creative Commons Attribution 3.0">CC BY 3.0</a>, <a href="https://commons.wikimedia.org/w/index.php?curid=5204616">Link</a>