ardupilot/libraries/AP_RangeFinder/AP_RangeFinder_HC_SR04.cpp

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/*
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
/*
* AP_RangeFinder_HC_SR04.cpp - rangefinder for HC_SR04 source
*
* https://cdn.sparkfun.com/datasheets/Sensors/Proximity/HCSR04.pdf
*
* There are two pins involved - one we attach an interrupt handler
* to and use for measuring the supplied interval which is
* proportional to distance.
*
* The second pin we use for triggering the ultransonic pulse
*/
#include <AP_HAL/AP_HAL.h>
#include "AP_RangeFinder.h"
#include "AP_RangeFinder_Params.h"
#include "AP_RangeFinder_HC_SR04.h"
#include <GCS_MAVLink/GCS.h>
extern const AP_HAL::HAL& hal;
AP_RangeFinder_HC_SR04::AP_RangeFinder_HC_SR04(RangeFinder::RangeFinder_State &_state, AP_RangeFinder_Params &_params) :
AP_RangeFinder_Backend(_state, _params)
{
set_status(RangeFinder::Status::NoData);
}
bool AP_RangeFinder_HC_SR04::check_pins()
{
check_trigger_pin();
return check_echo_pin() && trigger_pin > 0;
}
void AP_RangeFinder_HC_SR04::check_trigger_pin()
{
if (params.stop_pin == trigger_pin) {
// no change
return;
}
trigger_pin = params.stop_pin;
}
bool AP_RangeFinder_HC_SR04::check_echo_pin()
{
return pwm_source.set_pin(params.pin, "HC_SR04");
}
/*
detect if an HC_SR04 rangefinder is connected. The only thing we
can do is check if the pin number is valid. If it is, then assume
that the device is connected
*/
bool AP_RangeFinder_HC_SR04::detect(AP_RangeFinder_Params &_params)
{
if (_params.pin == -1) {
return false;
}
if (_params.stop_pin == -1) {
return false;
}
return true;
}
/*
update distance_cm
*/
void AP_RangeFinder_HC_SR04::update(void)
{
// check if pin has changed and configure interrupt handlers if required:
if (!check_pins()) {
// disabled (either by configuration or failure to attach interrupt)
state.distance_cm = 0.0f;
return;
}
const uint32_t value_us = pwm_source.get_pwm_us();
const uint32_t now = AP_HAL::millis();
if (value_us == 0) {
// no reading; check for timeout:
if (now - last_reading_ms > 1000) {
// no reading for a second - something is broken
state.distance_cm = 0.0f;
}
} else {
// gcs().send_text(MAV_SEVERITY_WARNING, "Pong!");
// a new reading - convert time to distance
state.distance_cm = value_us * (1.0/58.0f); // 58 is from datasheet, mult for performance
// glitch remover: measurement is greater than .5m from last.
// the SR-04 seeems to suffer from single-measurement glitches
// which can be removed by a simple filter.
if (labs(int32_t(uint32_t(state.distance_cm) - last_distance_cm)) > 50) {
// if greater for 5 readings then pass it as new height,
// otherwise use last reading
if (glitch_count++ > 4) {
last_distance_cm = state.distance_cm;
} else {
state.distance_cm = last_distance_cm;
}
} else {
// is not greater 0.5m, pass on and reset glitch counter
last_distance_cm = state.distance_cm;
glitch_count = 0;
}
last_reading_ms = now;
}
// update range_valid state based on distance measured
update_status();
// consider sending new ping
if (now - last_ping_ms > 67) { // read ~@15Hz - recommended 60ms delay from datasheet
last_ping_ms = now;
// gcs().send_text(MAV_SEVERITY_INFO, "Ping!");
// raise stop pin for n-microseconds
hal.gpio->pinMode(trigger_pin, HAL_GPIO_OUTPUT);
hal.gpio->write(trigger_pin, 1);
hal.scheduler->delay_microseconds(10);
hal.gpio->write(trigger_pin, 0);
}
}