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128 lines
4.5 KiB
Markdown
128 lines
4.5 KiB
Markdown
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[](https://github.com/marketplace/actions/arduino_ci)
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[](https://github.com/RobTillaart/SRF05/blob/master/LICENSE)
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[](https://github.com/RobTillaart/SRF05/releases)
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# SRF05
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Arduino library for the SRF05 distance sensor (and compatibles)
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## Description
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Class to use the distance sensor SRF05 and compatibles.
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The library allows to adjust the speed of the sound waves.
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Reasons to use a different value are temperature, humidity,
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type of gas, composition etc.
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Default value for the SOS is set to 343 m/s. (~20°C)
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Several correction formulas for the SOS are available on the internet
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v = 331.3 + 0.606 \* temperature °C (m/s)
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v = 331.4 + 0.606 \* temperature °C + 0.0124 \* rel_humidity (m/s)
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In fact humidity has an effect which increases with temperature.
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https://forum.arduino.cc/t/ultrasonic-sensor-to-determine-water-level/64890/12
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| temp | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
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|:----:|:------:|:------:|:------:|:------:|:------:|:------:|:------:|:------:|:------:|
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| 0 | 331.5 | 331.5 | 331.5 | 331.6 | 331.6 | 331.6 | 331.7 | 331.7 | 331.7 |
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| 5 | 334.5 | 334.6 | 334.6 | 334.7 | 334.7 | 334.7 | 334.8 | 334.8 | 334.9 |
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| 10 | 337.5 | 337.6 | 337.7 | 337.7 | 337.8 | 337.9 | 337.9 | 338.0 | 338.0 |
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| 15 | 340.5 | 340.6 | 340.7 | 340.8 | 340.9 | 341.0 | 341.1 | 341.2 | 341.2 |
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| 20 | 343.5 | 343.6 | 343.7 | 343.9 | 344.0 | 344.1 | 344.2 | 344.4 | 344.5 |
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| 25 | 346.4 | 346.6 | 346.8 | 347.0 | 347.1 | 347.3 | 347.5 | 347.6 | 347.8 |
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| 30 | 349.4 | 349.6 | 349.9 | 350.1 | 350.3 | 350.5 | 350.8 | 351.0 | 351.2 |
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(from https://www.engineeringtoolbox.com/air-speed-sound-d_603.html)
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The library has several ways to improve the quality of the measurements.
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By taking the average or the median of multiple readings.
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The library allows to set a correction factor to compensate for the timing of
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the **pulseIn()** function. This has in the end the same effect as changing the
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speed of sound however it is technically more correct to split the two.
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## Interface
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- **SRF05(const uint8_t trigger, const uint8_t echo, const uint8_t out = 0)** constructor to set the trigger and echo pin.
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It is not clear yet what the purpose of the OUT pin is.
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### Configuration
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- **void setSpeedOfSound(float sos)** adjust the speed of sound.
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- **float getSpeedOfSound()** return set value.
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- **void setCorrectionFactor(float cf = 1)** adjust the timing by a few percentage e.g. to adjust clocks. Should not be used to correct the speed of sound :)
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- **float getCorrectionFactor()** returns the set correction factor.
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normally a single read should be OK.
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- **void setModeSingle()** read single time.
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- **void setModeAverage(uint8_t cnt)** read cnt times and take the average.
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- **void setModeMedian(uint8_t cnt)** read cnt times and take the median. cnt = 3..15
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- **void setModeRunningAverage(float alpha)** use a running average algorithm with a weight (depends on your application).
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- **uint8_t getOperationalMode()** return the operational mode 0..3.
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### Get distance
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- **uint32_t getTime()** returns distance in microseconds.
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- **uint32_t getMillimeter()** returns distance in millimeter.
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- **float getCentimeter()** returns distance in centimeter.
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- **float getMeter()** returns distance in meter.
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- **float getInch()** returns distance in inches. (1 inch = 2.54 cm).
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- **float getFeet()** returns distance in feet. (1 feet = 12 inch).
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### Experimental - calibration
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Experimental, put the sensor at exactly 1 meter from a wall,
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and based upon the timing it will give an estimate for the
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speed of sound. Current version seems accurate within 3 - 5 %.
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- **float determineSpeedOfSound()**
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### Experimental - configuration
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### Performance
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Assumes default speed of sound of 340 m/sec
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| Distance | time (us) |
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|:--------:|----------:|
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| 1 | 2.94 |
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| 2 | 5.88 |
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| 5 | 14.71 |
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| 10 | 29.41 |
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| 20 | 58.82 |
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| 50 | 147.06 |
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| 100 | 294.12 |
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| 200 | 588.24 |
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| 300 | 882.35 |
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| 400 | 1176.47 |
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## Operational
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See examples..
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## TODO
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- print feet as 3'2" or 3-7/8 feet
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- enumerate mode operandi.
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- investigate purpose of the OUT pin.
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- example sketch with a DHT22 and the formula for SOS
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- fix magic conversion numbers.
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