DFRobot URM Ultrasonic Sensors: High-Performance and Diverse Selection

Ultrasonic technology, with its excellent directionality, low attenuation coefficient, and powerful penetration, finds extensive applications in various industries, including security, environmental monitoring, and industrial sectors. The market offers several types of ultrasonic sensors, such as the low-cost HC-SR04, high-precision SRF05, waterproof JSN-SR04T, and temperature-compensated HCSR-04S. However, these individual ultrasonic sensors can only meet specific range requirements and lack a series of products tailored for different scenarios, posing challenges for engineers in project development.

To address this issue, DFRobot has introduced the URM series of ultrasonic sensors. This series considers various application scenarios and demands, offering multiple models and functions for engineers to compare and choose from, thereby efficiently meeting diverse application requirements.

What is the URM series?

The URM series is a range of ultrasonic distance measurement modules specifically designed for industrial control and robot control applications. These modules are equipped with internal temperature compensation functionality, allowing for accurate measurement of the distance between the sensor and the target object. They can be widely used in various scenarios, such as robot barrier navigation, liquid level detection, and obstacle avoidance designs.

Since the introduction of the first URM37 module in 2009, DFRobot has continuously released 14 models of the URM series of ultrasonic distance measurement modules. These modules cover a wide range of measurement distances, beam angles, accuracy levels, and interface options, catering to the requirements of different application scenarios.

7 characteristics of URMs

1. Multiple measurement ranges

The range of ultrasonic distance measurement is a crucial parameter in ultrasound applications, and the URM series ultrasonic modules offer a variety of short, medium, and long-range options. Please refer to the table below for specific distances:

Note:
1.The units for the above data are centimeters (cm).

2.The actual measured distance by URM may be greater than the indicated data.

2. Multiple interfaces and signal outputs

The URM series of ultrasonic sensors offer a variety of signal output options, including I2C, UART, analog, pulse signal, RS485, and more. Considering the principle of ultrasonic distance measurement, the accuracy of distance can be affected by environmental temperature. URM sensors have built-in temperature sensors to measure ambient temperature and automatically compensate for distance errors based on temperature changes. Additionally, some sensors feature dedicated servo interfaces (URM37) or have the capability to automatically detect environmental and power supply noise and dynamically calibrate sensor parameters (URM13). These features make the URM series suitable for a wide range of applications.

3. Multiple beam angles

Ultrasonic sensors and bats operate on a similar principle of echolocation. They both emit high-frequency noise and measure the time it takes for the sound waves to bounce back from objects to work.

The beam angle refers to the spreading or coverage range of the emitted sound waves from an ultrasonic sensor. When the sound waves are emitted from the sensor, they form a conical beam that expands as the distance increases. The size of the beam angle directly affects the width of the conical region.

The beam angle is typically used to indicate the angular range within which the sensor can accurately detect objects. It represents the maximum angle range within which the emitted sound waves can effectively detect objects and provide reliable distance measurement results. Objects beyond the beam angle range may not be detected or may result in inaccurate measurements.

A smaller beam angle means a more concentrated and focused detection area, enabling higher precision distance measurements suitable for objects within that range. Conversely, a larger beam angle covers a broader area but may sacrifice accuracy at greater distances.

The URM series offers various beam angles: 12°, 15°, 20°, and 60°. Users can choose the appropriate beam angle based on their specific project requirements. The diagram below illustrates the detection range of select URM series modules.

Figure: URM08 Beam Angle: 60°

Figure: URM15 Beam Angle: 20°

 Figure: URM12 Beam Angle: 15°

Figure: URM14 Beam Angle: 12°

4. High-quality probes

An ultrasonic probe is a device used to emit and receive ultrasonic waves for detection. It consists of an absorptive material, a housing, damping blocks, and a piezoelectric chip. The absorptive material absorbs ultrasonic wave noise, while the housing provides support, fixation, protection, and electromagnetic shielding functions. The damping blocks reduce chip residual vibration and noise to improve resolution. The piezoelectric chip is the core component of the probe, capable of emitting ultrasonic waves and receiving the reflected ultrasonic wave signals. The performance of the probe is crucial for ultrasonic detection. Therefore, the term "ultrasonic probe" typically refers to the transducer part inside the sensor.

URM utilizes high-quality probes to ensure stability and performance. The main performance indicators of the probe include the following:

• Working frequency, also known as the resonant frequency of the piezoelectric chip.

When the frequency of the AC voltage applied to its terminals is equal to the resonant frequency of the chip, the output energy reaches its maximum and the sensitivity is also highest.

• Sensitivity, which is the minimum effective value measured by the ultrasonic sensor.

Its main factors are the piezoelectric material and the amplification circuit.

Taking URM07 as an example, the relevant parameters are as follows:

• Transmitting Sensitivity: 117dB Min. (40KHz 10Vp-p/30cm 0 dB=10V/Pa)
• Receiving Sensitivity: -66dB Min. (40KHz 10Vp-p/30cm 0 dB=10V/Pa)

Operating Temperature: The piezoelectric effect of the piezoelectric material can only be generated within a certain temperature range. When the temperature exceeds a certain threshold, the piezoelectric effect disappears. The temperature at which the piezoelectric effect disappears is called the Curie temperature.

The operating temperature of URM07 is -20°C to +80°C.

5. Durability

The URM series ultrasonic modules are manufactured using PCB gold immersion process, which provides corrosion resistance and ensures a long service life.

6. Noise-free distance readings

By combining the generated sound waves with continuously changing gain, real-time waveform analysis, and real-time noise suppression algorithms, the URM series ultrasonic modules are able to provide accurate and noise-free distance readings for most users.

7. Documentation

The URM series sensors already have various existing resources available, such as sample codes, wiki tutorials, selection guides, and more, all of which can be found on the DFRobot official website. They are compatible with platforms like Arduino and graphical programming platforms, making them relatively easy to get started with.

URM09&URM07

Two of the most representative ultrasonic sensors in the URM series are URM07 and URM09.

URM09

The URM09 ultrasonic sensor is the most cost-effective and user-friendly option among the URM series. It features analog output, eliminating the need for programming skills and complex communication protocols, making it easy to get started. This series offers three communication options to choose from:

• 0-VCC analog output
• I2C interface output
• Trig pulse output.

The URM09 analog ultrasonic sensor has an effective measuring range of 2cm to 500cm, with a 0-VCC analog output. Currently, there are various data transmission methods available in the market for ultrasonic sensors, such as RS485, pulse signals, UART, and more. However, they generally require technical and programming skills to get started. Without the corresponding software development libraries, the usage difficulty can be relatively high.

The URM09 analog ultrasonic sensor adopts the output method of a range of 0-VCC analog voltage. By using a simple conversion formula (Distance Conversion Formula: Distance = Output Voltage x 520 / Supply Voltage), users can obtain distance values. Users only need to know how to read and use a multimeter.

The analog transmission also has an advantage: it allows for easy implementation of multi-channel distance detection. For example, Arduino UNO, micro:bit, and STM32 all have multiple channels for analog signal acquisition (such as A0-A5 for UNO, P0, P1, and P2 for micro:bit). This means that the URM09 analog ultrasonic sensor can be conveniently applied to different microcontrollers.

Note: If you are using Raspberry Pi 4B or ESP32 as your mainboard, you need to choose an ADC acquisition module to convert the voltage value for connecting the analog sensor through the I2C communication method.

URM07

The URM07 is a professional-grade single-probe ultrasonic distance sensor with an effective measurement range of 20cm to 750cm, a measurement angle of 60 degrees, and UART communication.

In scenarios such as blind guidance, room ventilation, obstacle avoidance for vehicles, automatic doors, and water level monitoring, there is often a need for ultrasonic sensors that can measure longer distances and require high stability. The URM07 can measure distances beyond five meters with a distance resolution of 1cm and a measurement error of 1%. It also has a built-in temperature sensor that can collect ambient temperature values and automatically compensate for distance errors based on temperature changes.

Furthermore, the URM07 adopts a low-power circuit design, with an average operating current of only 5mA and a standby current of only 14uA. Even when powered by a 1000mA battery, the URM07 can work continuously for approximately 200 hours, making it highly suitable for projects with sensitive power consumption requirements, such as smart blind canes used by the visually impaired.

The default address of the URM07 ultrasonic sensor is 0x11, but it supports arbitrary address modification through serial commands, allowing for multi-point distance measurement requirements.

In the market, ultrasonic sensors with long-range capabilities and high stability are generally quite expensive, but the URM07 provides a relatively economical option.

Conclusion

When selecting the right type and series of ultrasonic sensors, it is crucial to consider factors like cost, functional requirements, and user-friendliness to meet the diverse needs of different application scenarios. Begin by assessing the project budget and economic feasibility to determine a cost range that is affordable. Next, clearly define the functional requirements, including the desired measurement range, accuracy, and interface options. Additionally, take into account the technical expertise of the engineers and any time constraints associated with the project, in order to choose sensor models and series that are easy to use and integrate seamlessly.

When comparing various manufacturers and models of ultrasonic sensors, it is beneficial to consult technical specifications, user reviews, and real-world application cases to make well-informed decisions. Ultimately, strike a balance between cost, functional requirements, and ease of use in order to select the most suitable ultrasonic sensor that fulfills the project's needs. In this context, the URM series of ultrasonic sensors stands out with its notable advantages such as high stability, extensive functionality, and user-friendly nature, making them particularly suitable for applications that demand superior ranging performance and module functionality.