Driver for a PWM based sonar range sensor

Reads sensor using PWM input and outputs sonar distance to object in [cm]

Why PWM over ADC: One only needs to connect GND, VCC and one more signal wire, same as ADC but not the disadvantages of ADC sensors noise

Sensor example: Maxbotix LV-EZ1

Example for airframe file

Add to your firmware section: This example contains all possible configuration options, not all of them are mandatory!

<module name="sonar_pwm">
  b'<define name="USE_SONAR" value="TRUE" />\n    '
  b'<define name="SONAR_OFFSET" value="0.1234" />\n    '
  b'<define name="SONAR_SCALE" value="SONAR_PWM_PERIOD" />\n    '
  b'<define name="SONAR_MIN_RANGE" value="0.44" unit="m" />\n    '
  b'<define name="SONAR_MAX_RANGE" value="3.0" unit="m" />\n    '
  b'<define name="SONAR_COMPENSATE_ROTATION" value="TRUE" />\n    '
  b'<define name="SONAR_UPDATE_ON_AGL" value="TRUE" />\n    '
  b'<define name="SONAR_PWM_PERIOD" value="4096" />\n    '
  b'<define name="SONAR_PWM_OFFSET" value="20" />\n    '
  b'<define name="SONAR_USE_PWM_FILTER" value="TRUE" />\n    '
  b'<define name="SONAR_MEDIAN_SIZE" value="9" />\n    '
  b'<define name="SENSOR_SYNC_SEND_SONAR" />\n  '
  b'<configure name="SONAR_PWM_CHANNEL" value="PWM_INPUTx" />\n    '
</module>

Module configuration options

Configure Options

name: SONAR_PWM_CHANNEL value: PWM_INPUTx
Description: Select PWM input channel for sensor to use e.g. PWM_INPUT1

Define Options

name: USE_SONAR value: TRUE
Description: Activate use of sonar in INS extended filter (only rotorcraft) or not if one only wants to measure distance
name: SONAR_OFFSET value: 0.1234
Description: Sensor offset in CM, as in where one onts zero to be, default is 0
name: SONAR_SCALE value: SONAR_PWM_PERIOD
Description: Sensor scale
name: SONAR_MIN_RANGE value: 0.44
Description: If defined, set limit to minimum value reported, default 0.15
name: SONAR_MAX_RANGE value: 3.0
Description: If defined, set limit to maximum value reported, default 6.0
name: SONAR_COMPENSATE_ROTATION value: TRUE
Description: Compensate AGL for body rotation, if not defined, defaults to FALSE
name: SONAR_UPDATE_ON_AGL value: TRUE
Description: Updates the AGL value in state,if not defined, defaults to FALSE
name: SONAR_PWM_PERIOD value: 4096
Description: period in microsec (e.g. 4096 for 12 bits sensor)
name: SONAR_PWM_OFFSET value: 20
Description: initial offset on the raw pwm signal if needed (default: 820usec)
name: SONAR_USE_PWM_FILTER value: TRUE
Description: Enable or disable a median filter on the sensor output values
name: SONAR_MEDIAN_SIZE value: 9
Description: If median filter is enabled then set this option to filter the output more(or less), default is 7
name: SENSOR_SYNC_SEND_SONAR value: None
Description: If defined, sends raw and scaled sonar values, useful for debugging sensor issues

Module functions

Init Functions

These initialization functions are called once on startup.

sonar_pwm_init()

Periodic Functions

These functions are called periodically at the specified frequency from the module periodic loop.

sonar_pwm_read()
- Frequency in Hz: 20
- Autorun: LOCK
  Periodic function automatically starts after init and can't be stopped.

Files

Header Files

The following headers are automatically included in modules.h

sonar_pwm.h

Source Files

modules/sonar/sonar_pwm.c

Raw sonar_pwm.xml file:

<!DOCTYPE module SYSTEM "module.dtd">
 
<module name="sonar_pwm" dir="sonar" task="sensors">
  <doc>
    <description>
      Driver for a PWM based sonar range sensor
      Reads sensor using PWM input and outputs sonar distance to object in [cm]
 
      Why PWM over ADC:
      One only needs to connect GND, VCC and one more signal wire, same as ADC but not the disadvantages of ADC sensors noise
 
      Sensor example: Maxbotix LV-EZ1
    </description>
    <configure name="SONAR_PWM_CHANNEL" value="PWM_INPUTx" description="Select PWM input channel for sensor to use e.g. PWM_INPUT1"/>
    <define name="USE_SONAR" value="TRUE" description="Activate use of sonar in INS extended filter (only rotorcraft) or not if one only wants to measure distance"/>
    <define name="SONAR_OFFSET" value="0.1234"  description="Sensor offset in CM, as in where one onts zero to be, default is 0"/>
    <define name="SONAR_SCALE" value="SONAR_PWM_PERIOD" description="Sensor scale"/>
    <define name="SONAR_MIN_RANGE" value="0.44" unit="m" description="If defined, set limit to minimum value reported, default 0.15"/>
    <define name="SONAR_MAX_RANGE" value="3.0" unit="m" description="If defined, set limit to maximum value reported, default 6.0"/>
    <define name="SONAR_COMPENSATE_ROTATION" value="TRUE" description="Compensate AGL for body rotation, if not defined, defaults to FALSE"/>
    <define name="SONAR_UPDATE_ON_AGL" value="TRUE" description="Updates the AGL value in state,if not defined, defaults to FALSE"/>
    <define name="SONAR_PWM_PERIOD" value="4096" description="period in microsec (e.g. 4096 for 12 bits sensor)"/>
    <define name="SONAR_PWM_OFFSET" value="20" description="initial offset on the raw pwm signal if needed (default: 820usec)"/>
    <define name="SONAR_USE_PWM_FILTER" value="TRUE" description="Enable or disable a median filter on the sensor output values"/>
    <define name="SONAR_MEDIAN_SIZE" value="9" description="If median filter is enabled then set this option to filter the output more(or less), default is 7"/>
    <define name="SENSOR_SYNC_SEND_SONAR" description="If defined, sends raw and scaled sonar values, useful for debugging sensor issues"/>
  </doc>
 
  <dep>
    <depends>pwm_meas</depends>
    <provides>sonar</provides>
  </dep>
  <header>
    <file name="sonar_pwm.h" />
  </header>
 
  <init fun="sonar_pwm_init()" />
  <periodic fun="sonar_pwm_read()" freq="20" />
 
  <makefile target="ap">
    <file name="sonar_pwm.c" />
    <define name="SONAR_PWM_CHANNEL" value="$(SONAR_PWM_CHANNEL)" cond="ifdef SONAR_PWM_CHANNEL" />
    <define name="$(SONAR_PWM_CHANNEL)_TICKS_PER_USEC" value="1" />
    <define name="USE_$(SONAR_PWM_CHANNEL)" value="PWM_PULSE_TYPE_ACTIVE_LOW" />
  </makefile>
</module>