US-100 Ultrasonic Range Finder Module

The US-100 Ultrasonic Range Finder Module is a high-precision distance measurement sensor that uses ultrasonic sound waves to detect and measure the distance to nearby objects from 2 cm up to 450 cm (15 ft) with 1 mm accuracy. It supports both pulse-width (ping) and serial UART communication modes, allowing flexible integration with various microcontrollers such as Arduino, ESP32, Raspberry Pi, and STM32. Unlike optical sensors, the US-100 is unaffected by light or color, ensuring reliable operation in diverse environments. Its built-in temperature sensor automatically compensates for air temperature variations, maintaining consistent accuracy. Compact, efficient, and easy to interface, the US-100 is perfect for robotic obstacle avoidance, distance measurement, and smart automation systems. Featured By RoboticsBD.

Product Images are shown for illustrative purposes only and may differ from the actual product.

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Features:

1. Dual Communication Modes: Supports serial (UART) and pulse-width interfaces.

2. Long Detection Range: Measures distances from 2 cm – 450 cm (up to 15 ft).

3. High Measurement Accuracy: 1 mm resolution for precise range detection.

4. Built-in Temperature Sensor: Provides automatic compensation for accurate readings.

5. Narrow Detection Cone: 15° field of view for focused detection.

6. Low Power Consumption: Draws less than 3 mA at 5 V.

7. Simple Integration: Works with Arduino, ESP32, STM32, and Raspberry Pi.

8. Selectable Modes via Jumper: Jumper installed = Serial Mode; removed = Pulse-Width Mode.

9. 40 kHz Ultrasonic Operation: Immune to visible light interference.

10. Compact Design: Easily mountable and ideal for mobile robots.

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Applications:

1. Obstacle Avoidance: Detects barriers for autonomous robots and vehicles.

2. Distance Measurement: Useful in parking sensors and automation setups.

3. Smart Home Systems: Enables motion or proximity-based automation.

4. Industrial Monitoring: Non-contact distance sensing for process control.

5. Educational Projects: Great for learning ultrasonic measurement techniques.

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Please allow 5% measuring deviation due to manual measurement.

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Documentation:

The way the pulse-width interface on the module works is as follows:

1. Jumper is removed
2. The module is normally idle.
3. A 10 uSec or wider pulse is sent to the TRIG pin on the module, usually by a microcontroller.  This will cause the module to start a detection cycle.
4. The module emits eight bursts of 40KHz sound and sets it’s ECHO pin output HIGH.
5. When the signal is reflected back from an object and is detected by the module, the ECHO pin is set back to LOW.
6. By measuring the amount of time that the ECHO pin is held HIGH, the distance to the object can be calculated using basic formula  (Time that ECHO is held HIGH * Speed of sound / 2)  The divide by 2 is because the sound has to travel in both directions (both out and back) and we want to know just the out distance.

If an echo is not returned (no object detected), the module will still lower the ECHO pin after a fixed delay.  This delay may vary, but is about 200mSec on the modules that I have measured.  This is required to prevent the module from hanging.

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The way the serial interface works is as follows:

1. Jumper is installed.
2. A serial command ‘0x55’ is sent to the module to initiate a reading.
3. The serial port is checked for the returned data that comes back in 2 bytes.  An MSB and a LSB byte.
4. The 2 bytes are added together to get the measurement in millimeters after shifting the MSB byte over by multiplying it by 256 similar to this (MSByte * 256) + LSByte
5. If the temperature reading is desired, a serial command of ‘0x50’ is sent to initiate a temperature reading.
6. The serial port is checked for the returned data that comes back as a single byte.
7. A constant value of 45 is subtracted from the byte to get the temperature in degrees C.

There is a 5-pin header on the assembly.  The GND pins are connected to the system ground and the Vcc pin is connected to 5V.  The TRIG/TX pin has different functions depending on whether the jumper on the back of the module is installed or not.  If the jumper is installed, it is the serial TX pin that connects to TX pin on a microcontroller.  If the jumper is removed, it is the input Trigger pin on which a 10uSec pulse is applied to start the measurement cycle.  The ECHO/RX pin also has different functions depending on the jumper on the back of the module.  If the jumper is installed, it is the RX pin that connects to the RX pin on the microcontroller.  If the jumper is removed it is an output pin that is held HIGH for the duration of the time from when the module sends a 40KHz pulse out until it receives the echo back.

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Module Connections

1 x 5 Header

• VCC –   Connect to 5V.
• TRIG / TX –   Connects to digital output pin.  A 10uSec or wider pulse starts a measurement cycle / Or acts as the TX pin for serial comm
• ECHO / RX –  Connect to digital input pin.  This pin is held high for the duration of the the measurement cycle / Or acts as the RX pin for serial comm.
• GND –   Connect to system ground.  This ground needs to be in common with the microcontroller.
• GND –  Second ground pin is common with the other ground pin on the module and does not need to be connected.

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OUR EVALUATION RESULTS:

This is a commonly used module for obstacle detection and basic range finding.  These are much more capable than the basic IR obstacle avoidance sensors that come in sensor kits and are highly recommended if you are building a motorized robotic car and want to implement a nicely capable obstacle avoidance system or just want to measure distance for some other reason.

The module has a small microprocessor which does all the heavy lifting of managing the ultrasonic and temperature sensors, doing the calculations when using serial mode and managing serial I/O.

The serial I/O is a significant improvement over using the pulse-width interface and its use is highly recommended.  Given that, the pulse-width method is also interesting to implement and experiment with and this module lets you do both.  A program that implement the pulse width interface can be found on our HY-SRF05 page and is compatible with this sensor.

As an interesting aside, it has been noticed that when using serial mode, if the 5V power is removed the module continues to work, apparently due to parasitic power being pulled off the serial comm lines.

The program below implements a serial interface with the module and displays the measured range in millimeters, centimeters and inches on the Serial Monitor.  To use the serial mode of operation, ensure that the jumper is installed on the back of the module.

Note that we use SoftSerial library to implement a software serial port.  This is mainly required when using on an UNO or other MCU with a single hardware serial port to avoid conflict between the sensor serial port and the USB serial port.  If using a Mega or some other microcontroller with  multiple hardware serial ports, you can use one of those instead if you prefer.

SoftSerial does require interrupt capability on the incoming RX line so we are using pins 10 for TX and 11 or RX since most of the Arduino series supports interrupts on both of these pins.  You will also need to connect 5V to Vcc and Ground to one of the GND pins.

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US-100 Ultrasonic Range Finder Module Program

/*
 * US-100 Ultrasonic Test - Serial Interface Mode
 *
 * Exercises the ultrasonic range finder module in serial mode 
 * and prints out the current measured distance and temperature
 * This uses 'softserial' to communicate with the module to avoid any conflict 
 * with the HW serial port if using an UNO. 
 * VCC - connect to 5V
 * GND - connect to ground.  The 2 grounds are tied together on the module
 * TRIG/TX - connect to digital pin 10
 * ECHO/RX - connect to digital pin 11
 * 
 * For Serial mode of operation, ensure the jumper is installed on the back
 * of the module
 */ 
#include <SoftwareSerial.h>;
const int US_100_TX = 10;      // Pin for Soft Serial TX
const int US_100_RX = 11;      // Pin for Soft Serial RX
 // Create instance of soft serial port for comm with module
SoftwareSerial US_100_Port(US_100_RX, US_100_TX);
 
unsigned int MSByte = 0;  // Most Significant Byte of distance measurement
unsigned int LSByte = 0;  // Least Significant Byte of distance measurement
unsigned int mmDist = 0;      // Returned distance in millimeters
int temp = 0;                 // Returned temp measurement
//===============================================================================
//  Initialization
//=============================================================================== 
void setup() {
    Serial.begin(9600);       // Initialize the serial ports
    US_100_Port.begin(9600);
}
//===============================================================================
//  Main
//=============================================================================== 
void loop() {
 
    US_100_Port.flush();      // Clear the port buffer   
    US_100_Port.write(0x55);  // Request distance measurement
    delay(500);               // Give the sensor a little time to make the measurement
 
    if(US_100_Port.available() >= 2)      // Looking for 2 bytes to be returned
    {
        MSByte = US_100_Port.read();  // Read in the MSB (Most Significant Byte) data
        LSByte  = US_100_Port.read(); // Read in the LSB (Least Significant Byte) data
        mmDist  = MSByte * 256 + LSByte; // Calculate the distance from the two bytes
        if((mmDist > 20) && (mmDist < 4500)) // Check that reading is within a valid range.
        {
            Serial.print("Distance: "); // Printout distance in millimeters, centimeters and inches
            Serial.print(mmDist);
            Serial.print("mm   ");
            Serial.print(mmDist/10);
            Serial.print("cm   ");
            Serial.print(mmDist/25.4, 2);
            Serial.println("in");
        }
        else Serial.println("OUT OF RANGE");
    }
 
    US_100_Port.flush();      // Clear the serial port buffer
    US_100_Port.write(0x50);  // Request temperature measurement
    delay(500);
    if(US_100_Port.available() >= 1)     // Looking for 1 byte to be returned
    {
        temp = US_100_Port.read();       // Read the byte
        if((temp > 1) && (temp < 100))   // Check for valid temperature range
        {
            temp -= 45;                 // Temp data has to be offset by -45º
            Serial.print("Temperature: ");
            Serial.print(temp);
            Serial.println("C.");
            Serial.println("");
        }
    }
     delay(1000);
}

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Package Includes:

1 x US-100 Ultrasonic Range Finder Module

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