mirror of
https://github.com/DCC-EX/CommandStation-EX.git
synced 2024-11-24 16:46:13 +01:00
86c3020672
No functional change. VPINs are unsigned integers in the range 0-65535 (although the highest values are special, 65535=VPIN_NONE). Values above 32767 were erroneously being displayed as negative. This has been fixed, which is a pre-requisite for allowing VPINs above 32767 to be used.
244 lines
9.9 KiB
C++
244 lines
9.9 KiB
C++
/*
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* © 2021, Neil McKechnie. All rights reserved.
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*
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* This file is part of DCC++EX API
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*
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* This is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* It is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with CommandStation. If not, see <https://www.gnu.org/licenses/>.
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*/
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/*
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* The HC-SR04 module has an ultrasonic transmitter (40kHz) and a receiver.
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* It is operated through two signal pins. When the transmit pin is set to 1
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* for 10us, on the falling edge the transmitter sends a short transmission of
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* 8 pulses (like a sonar 'ping'). This is reflected off objects and received
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* by the receiver. A pulse is sent on the receive pin whose length is equal
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* to the delay between the transmission of the pulse and the detection of
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* its echo. The distance of the reflecting object is calculated by halving
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* the time (to allow for the out and back distance), then multiplying by the
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* speed of sound (assumed to be constant).
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*
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* This driver polls the HC-SR04 by sending the trigger pulse and then measuring
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* the length of the received pulse. If the calculated distance is less than
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* the threshold, the output _state returned by a read() call changes to 1. If
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* the distance is greater than the threshold plus a hysteresis margin, the
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* output changes to 0. The device also supports readAnalogue(), which returns
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* the measured distance in cm, or 32767 if the distance exceeds the
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* offThreshold.
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*
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* It might be thought that the measurement would be more reliable if interrupts
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* were disabled while the pulse is being timed. However, this would affect
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* other functions in the CS so the measurement is being performed with
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* interrupts enabled. Also, we could use an interrupt pin in the Arduino for
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* the timing, but the same consideration applies. In any case, the DCC
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* interrupt occurs once every 58us, so any IRC code is much faster than that.
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* And 58us corresponds to 1cm in the calculation, so the effect of
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* interrupts is negligible.
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*
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* Note: The timing accuracy required for measuring the pulse length means that
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* the pins have to be direct Arduino pins; GPIO pins on an IO Extender cannot
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* provide the required accuracy.
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*
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* Example configuration:
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* HCSR04::create(23000, 32, 33, 80, 85);
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*
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* Where 23000 is the VPIN allocated,
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* 32 is the pin connected to the HCSR04 trigger terminal,
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* 33 is the pin connected to the HCSR04 echo terminal,
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* 80 is the distance in cm below which pin 23000 will be active,
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* and 85 is the distance in cm above which pin 23000 will be inactive.
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*
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* Alternative configuration, which hogs the processor until the measurement is complete
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* (old behaviour, more accurate but higher impact on other CS tasks):
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* HCSR04::create(23000, 32, 33, 80, 85, HCSR04::LOOP);
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*
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*/
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#ifndef IO_HCSR04_H
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#define IO_HCSR04_H
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#include "IODevice.h"
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class HCSR04 : public IODevice {
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private:
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// pins must be arduino GPIO pins, not extender pins or HAL pins.
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int _trigPin = -1;
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int _echoPin = -1;
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// Thresholds for setting active _state in cm.
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uint8_t _onThreshold; // cm
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uint8_t _offThreshold; // cm
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// Last measured distance in cm.
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uint16_t _distance;
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// Active=1/inactive=0 _state
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uint8_t _value = 0;
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// Factor for calculating the distance (cm) from echo time (us).
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// Based on a speed of sound of 345 metres/second.
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const uint16_t factor = 58; // us/cm
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// Limit the time spent looping by dropping out when the expected
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// worst case threshold value is greater than an arbitrary value.
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const uint16_t maxPermittedLoopTime = 10 * factor; // max in us
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unsigned long _startTime = 0;
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unsigned long _maxTime = 0;
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enum {DORMANT, MEASURING}; // _state values
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uint8_t _state = DORMANT;
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uint8_t _counter = 0;
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uint16_t _options = 0;
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public:
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enum Options {
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LOOP = 1, // Option HCSR04::LOOP reinstates old behaviour, i.e. complete measurement in one loop entry.
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};
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// Static create function provides alternative way to create object
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static void create(VPIN vpin, int trigPin, int echoPin, uint16_t onThreshold, uint16_t offThreshold, uint16_t options = 0) {
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if (checkNoOverlap(vpin))
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new HCSR04(vpin, trigPin, echoPin, onThreshold, offThreshold, options);
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}
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protected:
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// Constructor performs static initialisation of the device object
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HCSR04 (VPIN vpin, int trigPin, int echoPin, uint16_t onThreshold, uint16_t offThreshold, uint16_t options) {
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_firstVpin = vpin;
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_nPins = 1;
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_trigPin = trigPin;
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_echoPin = echoPin;
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_onThreshold = onThreshold;
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_offThreshold = offThreshold;
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_options = options;
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addDevice(this);
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}
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// _begin function called to perform dynamic initialisation of the device
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void _begin() override {
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_state = 0;
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pinMode(_trigPin, OUTPUT);
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pinMode(_echoPin, INPUT);
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ArduinoPins::fastWriteDigital(_trigPin, 0);
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#if defined(DIAG_IO)
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_display();
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#endif
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}
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// _read function - just return _value (calculated in _loop).
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int _read(VPIN vpin) override {
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(void)vpin; // avoid compiler warning
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return _value;
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}
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int _readAnalogue(VPIN vpin) override {
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(void)vpin; // avoid compiler warning
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return _distance;
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}
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// _loop function - read HC-SR04 once every 100 milliseconds.
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void _loop(unsigned long currentMicros) override {
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unsigned long waitTime;
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switch(_state) {
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case DORMANT: // Issue pulse
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// If receive pin is still set on from previous call, do nothing till next entry.
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if (ArduinoPins::fastReadDigital(_echoPin)) return;
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// Send 10us pulse to trigger transmitter
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ArduinoPins::fastWriteDigital(_trigPin, 1);
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delayMicroseconds(10);
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ArduinoPins::fastWriteDigital(_trigPin, 0);
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// Wait, with timeout, for echo pin to become set.
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// Measured time delay is just under 500us, so
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// wait for max of 1000us.
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_startTime = micros();
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_maxTime = 1000;
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while (!ArduinoPins::fastReadDigital(_echoPin)) {
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// Not set yet, see if we've timed out.
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waitTime = micros() - _startTime;
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if (waitTime > _maxTime) {
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// Timeout waiting for pulse start, abort the read and start again
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_state = DORMANT;
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return;
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}
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}
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// Echo pulse started, so wait for echo pin to reset, and measure length of pulse
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_startTime = micros();
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_maxTime = factor * _offThreshold;
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_state = MEASURING;
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// If maximum measurement time is high, then skip until next loop entry before
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// starting to look for pulse end.
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// This gives better accuracy at shorter distance thresholds but without extending
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// loop execution time for longer thresholds. If LOOP option is set on, then
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// the entire measurement will be done in one loop entry, i.e. the code will fall
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// through into the measuring phase.
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if (!(_options & LOOP) && _maxTime > maxPermittedLoopTime) break;
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/* fallthrough */
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case MEASURING: // Check if echo pulse has finished
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do {
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waitTime = micros() - _startTime;
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if (!ArduinoPins::fastReadDigital(_echoPin)) {
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// Echo pulse completed; check if pulse length is below threshold and if so set value.
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if (waitTime <= factor * _onThreshold) {
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// Measured time is within the onThreshold, so value is one.
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_value = 1;
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// If the new distance value is less than the current, use it immediately.
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// But if the new distance value is longer, then it may be erroneously long
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// (because of extended loop times delays), so apply a delay to distance increases.
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uint16_t estimatedDistance = waitTime / factor;
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if (estimatedDistance < _distance)
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_distance = estimatedDistance;
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else
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_distance += 1; // Just increase distance slowly.
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_counter = 0;
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//DIAG(F("HCSR04: Pulse Len=%l Distance=%d"), waitTime, _distance);
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}
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_state = DORMANT;
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} else {
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// Echo pulse hasn't finished, so check if maximum time has elapsed
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// If pulse is too long then set return value to zero,
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// and finish without waiting for end of pulse.
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if (waitTime > _maxTime) {
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// Pulse length longer than maxTime, value is provisionally zero.
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// But don't change _value unless provisional value is zero for 10 consecutive measurements
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if (_value == 1) {
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if (++_counter >= 10) {
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_value = 0;
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_distance = 32767;
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_counter = 0;
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}
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}
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_state = DORMANT; // start again
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}
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}
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// If there's lots of time remaining before the expected completion time,
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// then exit and wait for next loop entry. Otherwise, loop until we finish.
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// If option LOOP is set, then we loop until finished anyway.
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uint32_t remainingTime = _maxTime - waitTime;
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if (!(_options & LOOP) && remainingTime < maxPermittedLoopTime) return;
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} while (_state == MEASURING) ;
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break;
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}
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// Datasheet recommends a wait of at least 60ms between measurement cycles
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if (_state == DORMANT)
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delayUntil(currentMicros+60000UL); // wait 60ms till next measurement
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}
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void _display() override {
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DIAG(F("HCSR04 Configured on VPIN:%u TrigPin:%d EchoPin:%d On:%dcm Off:%dcm"),
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_firstVpin, _trigPin, _echoPin, _onThreshold, _offThreshold);
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}
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};
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#endif //IO_HCSR04_H
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