HC-SR04 - Revision history

Kai: /* Wiring and Voltage Levels */

2025-05-02T17:39:56Z

Wiring and Voltage Levels

← Older revision		Revision as of 2025-05-02T17:39:56
Line 25:		Line 25:

	=== Wiring and Voltage Levels ===		=== Wiring and Voltage Levels ===
	The sensor module ~~has~~ four pins:		The sensor module is connected via the four header pins on the board:

	[[File:sensor_HC-SR04_pin_assignment.png \| 120px]]		[[File:sensor_HC-SR04_pin_assignment.png \| 120px]]

Kai: /* Wiring and Voltage Levels */

2025-05-02T17:27:23Z

Wiring and Voltage Levels

← Older revision		Revision as of 2025-05-02T17:27:23
Line 26:		Line 26:
	=== Wiring and Voltage Levels ===		=== Wiring and Voltage Levels ===
	The sensor module has four pins:		The sensor module has four pins:
	* ''Gnd'' for Ground,
	* ''Echo'' for the ultrasonic echo output signal,
	* ''Trig'' for the ultrasonic burst trigger signal input, and
	* ''Vcc'' for the 5 V supply voltage.

	[[File:sensor_HC-SR04_pin_assignment.png \| 120px]]		[[File:sensor_HC-SR04_pin_assignment.png \| 120px]]

			* ''Vcc'' for the 5 V supply voltage,
			* ''Trig'' for the ultrasonic burst trigger signal input,
			* ''Echo'' for the ultrasonic echo output signal, and
			* ''Gnd'' for Ground.

	<p style="text-align:justify; margin-top:1em">		<p style="text-align:justify; margin-top:1em">

Kai: updated the pin assignment image

2025-05-02T17:13:25Z

updated the pin assignment image

← Older revision		Revision as of 2025-05-02T17:13:25
Line 31:		Line 31:
	* ''Vcc'' for the 5 V supply voltage.		* ''Vcc'' for the 5 V supply voltage.

	~~<div class="row" "margin:1em; text-align:center;">~~		[[File:sensor_HC-SR04_pin_assignment.png \| 120px]]
	~~<div class="column small-6 small-centered medium-2 medium-centered large-2 large-centered">~~
	[[File:sensor_HC-SR04_pin_assignment.png \| ~~100px~~]]
	~~</div>~~
	~~</div>~~
	<p style="text-align:justify; margin-top:1em">		<p style="text-align:justify; margin-top:1em">
	The sensor circuit is designed for TTL-level signals (0 V for LOW and 5 V for HIGH) while the GPIO pins of most microcontrollers and single-board-computers (SBC) are designed for 3.3 V. We definitely need to drop the signal coming from the ''Echo'' pin to 3.3 V, otherwise we risk damaging the connected GPIO input. One would assume that we also need to transform the 3.3 V trigger signal from the GPIO to 5 V before feeding it to the ''Trig'' pin. Such a circuit is depicted below, where a simple voltage divider is used on ''Echo'' and a BJT transistor is used to step up the voltage for ''Trig''.		The sensor circuit is designed for TTL-level signals (0 V for LOW and 5 V for HIGH) while the GPIO pins of most microcontrollers and single-board-computers (SBC) are designed for 3.3 V. We definitely need to drop the signal coming from the ''Echo'' pin to 3.3 V, otherwise we risk damaging the connected GPIO input. One would assume that we also need to transform the 3.3 V trigger signal from the GPIO to 5 V before feeding it to the ''Trig'' pin. Such a circuit is depicted below, where a simple voltage divider is used on ''Echo'' and a BJT transistor is used to step up the voltage for ''Trig''.

Kai: /* Operation */

2025-05-02T15:20:10Z

Operation

← Older revision		Revision as of 2025-05-02T15:20:10
Line 48:		Line 48:
	The controller starts the range measurement by raising pin ''Trig'' to 5 V for at least 10 μs and thereby triggering eight 40 kHz ultrasonic pulses (beyond the 20 kHz high frequency limit of human hearing). The pulse waves bounce off any nearby objects and some are reflected back to the sensor. The sensor detects these reflected waves and raises the ''Echo'' pin to 5 V for a duration proportional to the distance of the objects that the waves are reflected from.		The controller starts the range measurement by raising pin ''Trig'' to 5 V for at least 10 μs and thereby triggering eight 40 kHz ultrasonic pulses (beyond the 20 kHz high frequency limit of human hearing). The pulse waves bounce off any nearby objects and some are reflected back to the sensor. The sensor detects these reflected waves and raises the ''Echo'' pin to 5 V for a duration proportional to the distance of the objects that the waves are reflected from.
	</p>		</p>
	~~<div class="row" "margin:2em; text-align:center;">~~		[[File:sensor_HC-SR04_timing.png \| 450px]]
	~~<div class="column small-10 small-centered medium-6 medium-centered large-6 large-centered">~~
	[[File:sensor_HC-SR04_timing.png \| 450px]]
	~~</div>~~
	~~</div>~~
	<p style="text-align:justify; margin-top:2em;">		<p style="text-align:justify; margin-top:2em;">
	A single range measurement is therefore performed like this:		A single range measurement is therefore performed like this:
Line 61:		Line 57:
	* Calculate the distance from the time that the ultrasonic waves spent travelling in air (distance = time * velocity / 2, where the velocity of ultrasonic waves in air is 340 m/s).		* Calculate the distance from the time that the ultrasonic waves spent travelling in air (distance = time * velocity / 2, where the velocity of ultrasonic waves in air is 340 m/s).
	</p>		</p>
	<p>		<p style="margin-top: 2em">
	This capture from an oscilloscope shows the short trigger pulse (blue), and the following long echo pulse (green) for an object placed approximately 12 cm in front of the sensor.		This capture from an oscilloscope shows the short trigger pulse (blue), and the following long echo pulse (green) for an object placed approximately 12 cm in front of the sensor.
	</p>		</p>

Kai: /* Operation */

2025-05-02T14:50:00Z

Operation

← Older revision		Revision as of 2025-05-02T14:50:00
Line 46:		Line 46:

	=== Operation ===		=== Operation ===
	The controller starts the range measurement by raising pin ~~TRIG~~ to 5 V for at least 10 μs and thereby triggering eight 40 kHz ultrasonic pulses (beyond the 20 kHz high frequency limit of human hearing). The pulse waves bounce off any nearby objects and some are reflected back to the sensor. The sensor detects these reflected waves and raises the ~~ECHO~~ pin to 5 V for a duration proportional to the distance of the objects that the waves are reflected from.		The controller starts the range measurement by raising pin ''Trig'' to 5 V for at least 10 μs and thereby triggering eight 40 kHz ultrasonic pulses (beyond the 20 kHz high frequency limit of human hearing). The pulse waves bounce off any nearby objects and some are reflected back to the sensor. The sensor detects these reflected waves and raises the ''Echo'' pin to 5 V for a duration proportional to the distance of the objects that the waves are reflected from.
	</p>		</p>
	<div class="row" "margin:2em; text-align:center;">		<div class="row" "margin:2em; text-align:center;">
Line 55:		Line 55:
	<p style="text-align:justify; margin-top:2em;">		<p style="text-align:justify; margin-top:2em;">
	A single range measurement is therefore performed like this:		A single range measurement is therefore performed like this:
	* Initialize by setting the ~~TRIG~~ and ~~ECHO~~ pins to LOW.		* Initialize by setting the ''Trig'' and ''Echo'' pins to LOW.
	* Raise the ~~TRIG~~ pin to HIGH for at least 10 μs.		* Raise the ''Trig'' pin to HIGH for at least 10 μs.
	* Wait for a rising edge on the ~~ECHO~~ pin, start a timer when detected.		* Wait for a rising edge on the ''Echo'' pin, start a timer when detected.
	* Wait for the falling edge on the ~~ECHO~~ pin, stop the timer when detected.		* Wait for the falling edge on the ''Echo'' pin, stop the timer when detected.
	* Calculate the distance from the time that the ultrasonic waves spent travelling in air (distance = time * velocity / 2, where the velocity of ultrasonic waves in air is 340 m/s).		* Calculate the distance from the time that the ultrasonic waves spent travelling in air (distance = time * velocity / 2, where the velocity of ultrasonic waves in air is 340 m/s).
	</p>		</p>

Kai: /* For Raspberry Pi Pico, using the C SDK */

2025-05-02T14:37:27Z

For Raspberry Pi Pico, using the C SDK

← Older revision		Revision as of 2025-05-02T14:37:27
Line 175:		Line 175:
	// calculating the distance		// calculating the distance
	auto duration = echoFallTime - echoRiseTime;		auto duration = echoFallTime - echoRiseTime;
	auto distance = (int)(duration * SpeedOfSound * / 2 / 1000000);		auto distance = (int)(duration * SpeedOfSound / 2 / 1000000);
	return distance;		return distance;
	}		}
	</syntaxhighlight>		</syntaxhighlight>

Kai: /* For Raspberry Pi Pico, using the C SDK */

2025-05-02T14:37:08Z

For Raspberry Pi Pico, using the C SDK

← Older revision		Revision as of 2025-05-02T14:37:08
Line 175:		Line 175:
	// calculating the distance		// calculating the distance
	auto duration = echoFallTime - echoRiseTime;		auto duration = echoFallTime - echoRiseTime;
	auto distance = (int)(SpeedOfSound * ~~duration~~ / ~~2000000~~);		auto distance = (int)(duration * SpeedOfSound * / 2 / 1000000);
	return distance;		return distance;
	}		}
	</syntaxhighlight>		</syntaxhighlight>

Kai: /* Operation */

2025-05-02T14:30:25Z

Operation

← Older revision		Revision as of 2025-05-02T14:30:25
Line 61:		Line 61:
	* Calculate the distance from the time that the ultrasonic waves spent travelling in air (distance = time * velocity / 2, where the velocity of ultrasonic waves in air is 340 m/s).		* Calculate the distance from the time that the ultrasonic waves spent travelling in air (distance = time * velocity / 2, where the velocity of ultrasonic waves in air is 340 m/s).
	</p>		</p>
	~~<br />~~
	<p>		<p>
	This capture from an oscilloscope shows the short trigger pulse (blue), and the following long echo pulse (green) for an object placed approximately 12 cm in front of the sensor.		This capture from an oscilloscope shows the short trigger pulse (blue), and the following long echo pulse (green) for an object placed approximately 12 cm in front of the sensor.

Kai: Adds text for the oscilloscope screen capture.

2025-05-02T14:29:57Z

Adds text for the oscilloscope screen capture.

← Older revision		Revision as of 2025-05-02T14:29:57
Line 60:		Line 60:
	* Wait for the falling edge on the ECHO pin, stop the timer when detected.		* Wait for the falling edge on the ECHO pin, stop the timer when detected.
	* Calculate the distance from the time that the ultrasonic waves spent travelling in air (distance = time * velocity / 2, where the velocity of ultrasonic waves in air is 340 m/s).		* Calculate the distance from the time that the ultrasonic waves spent travelling in air (distance = time * velocity / 2, where the velocity of ultrasonic waves in air is 340 m/s).
			</p>
			<br />
			<p>
			This capture from an oscilloscope shows the short trigger pulse (blue), and the following long echo pulse (green) for an object placed approximately 12 cm in front of the sensor.
	</p>		</p>
	[[File:Sensor_HC-SR04_signals.png \| x400px ]]		[[File:Sensor_HC-SR04_signals.png \| x400px ]]

Kai: /* Wiring and Voltage Levels */

2025-05-02T14:21:41Z

Wiring and Voltage Levels

← Older revision		Revision as of 2025-05-02T14:21:41
Line 37:		Line 37:
	</div>		</div>
	<p style="text-align:justify; margin-top:1em">		<p style="text-align:justify; margin-top:1em">
	The sensor circuit is designed for TTL-level signals (0 V for LOW and 5 V for HIGH) while the GPIO pins of most microcontrollers and single-board-computers are designed for 3.3 V. We definitely need to drop the signal coming from the ''Echo'' pin to 3.3 V, otherwise we risk damaging the connected GPIO input. One would assume that we also need to transform the 3.3 V trigger signal from the GPIO to 5 V before feeding it to the ''Trig'' pin. Such a circuit is depicted below, where a simple voltage divider is used on ''Echo'' and a BJT transistor is used to step up the voltage for ''Trig''.		The sensor circuit is designed for TTL-level signals (0 V for LOW and 5 V for HIGH) while the GPIO pins of most microcontrollers and single-board-computers (SBC) are designed for 3.3 V. We definitely need to drop the signal coming from the ''Echo'' pin to 3.3 V, otherwise we risk damaging the connected GPIO input. One would assume that we also need to transform the 3.3 V trigger signal from the GPIO to 5 V before feeding it to the ''Trig'' pin. Such a circuit is depicted below, where a simple voltage divider is used on ''Echo'' and a BJT transistor is used to step up the voltage for ''Trig''.
	</p>		</p>
	[[File:Sensor_HC-SR04_schematic_full_level_shifting.png \| x250px ]]		[[File:Sensor_HC-SR04_schematic_full_level_shifting.png \| x250px ]]