Pololu Distance Sensor with Pulse Width Output

by Pololu

This small lidar-based distance sensor reports the distance of objects with a pulsed signal similar to a hobby servo control signal.

A digital microcontroller pin can be used to time the length of each high pulse, which encodes the measured distance. The sensor works over an input voltage range of 3.0 V to 5.5 V, and the 0.1″ pin spacing makes it easy to use with standard solderless breadboards and 0.1″ perfboards.

Note: The maximum range is only achievable for high-reflectance objects in good ambient conditions. Lower-reflectivity targets or poor ambient conditions will reduce the maximum range.

It uses a short-range lidar module to precisely measure how long it takes for emitted pulses of infrared, eye-safe laser light to reach the nearest object and be reflected back, allowing for 1-3 mm resolution. As long as the sensor is enabled, it takes continuous distance measurements and encodes the ranges as the widths of high pulses, which can then be timed by a microcontroller using a single digital input.

The relationship between measured distance d (in mm) and pulse width t (in µs) is as follows:

50cm max 130cm max 300cm max
t=1000 µs + 4µs⁄3mm ⋅ d t=1000 µs + 1µs⁄2mm ⋅ d t=1000 µs + 1µs⁄4mm ⋅ d
d=3 mm⁄4µs ⋅ (t –1000 µs) d=2 mm⁄1µs ⋅ (t –1000 µs) d=4 mm⁄1µs ⋅ (t –1000 µs)

The timing uncertainty is approximately ±5%. As objects approach the sensor, the output pulse width will approach 1.0 ms, while an object detected at 50 cm will produce a 1.65-1.75 ms pulse width. The sensor uses a pulse width of 2.0 ms to indicate no detection. The pulse period T ranges from around 9 ms to 20 ms (for 5cm max), 9ms to 10ms (for 130max), or 30 to 33ms (for max 300cm), depending on the proximity of the detected object.

The maximum detection range depends on object reflectivity and ambient lighting conditions. In tests, the sensor was able to reliably detect a white sheet of paper out to around 50 cm away, and it could reliably detect a hand out to around 30 cm away. The following graph shows the measured distances of five units versus their actual distances from a white paper target at several different ranges:

Please note that while this sensor can detect objects almost all the way up to the sensor face, the effective minimum distance it can measure is around 1 cm, so objects closer than 1 cm might still result in a measured distance of around 1 cm.

Specifications

  • Operating voltage: 3.0 V to 5.5 V
  • Current consumption: 30 mA (typical) when enabled, 0.4 mA when disabled
  • Field of view (FOV): 15° typical; can vary with object reflectance and ambient conditions
  • Output type: digital pulse width
  • Dimensions: 0.85″ × 0.35″ × 0.122″ (21.6 × 8.9 × 3.1 mm); see the dimension diagram for more information
  • Weight: 0.014 oz (0.4 g)

Using the sensor

Important note: This product might ship with a protective liner covering the sensor IC. The liner must be removed for proper sensing performance.

Three connections are necessary to use this module: VIN, GND, and OUT. These pins are accessible through a row of 0.1″-pitch through holes, which work with standard 0.1″ (2.54 mm) male headers and 0.1″ female headers (available separately). The VIN pin should be connected to a 3 V to 5.5 V source, and GND should be connected to 0 volts. The sensor outputs its digital pulses on the OUT pin. The low level of the pulses is 0 V, and the high level is VIN. A red LED on the back side of the board also lights whenever an object is detected (the closer the object, the brighter the LED).

The board has an optional ENABLE pin that can be driven low to put it into a low-power state that consumes approximately 0.4 mA. This pin can be accessed through a via or its neighboring surface-mount pad on the back side labeled “EN” on the silkscreen. The ENABLE pin is pulled up to VIN, enabling the sensor by default.

The board features four surface-mount configuration jumpers that determine its operation mode. Different versions of the Pololu Digital Distance sensors ship with the appropriate jumpers pre-populated with 0 Ω resistors. These resistors can be desoldered from the populated spots or solder bridges can be added across the unpopulated spots to convert one sensor version into another. The table in the section below shows the jumper settings for the different versions.

The board has one mounting hole intended for use with #2 or M2 screws.

Arduino program for reading pulse width output

This is a simple Arduino sketch that reads the output of the Pololu Distance Sensor with Pulse Width Output, 50cm Max and displays the measured distance in millimeters.

// Example Arduino program for reading the Pololu Distance Sensor with Pulse Width Output, 50cm Max

// Change this to match the Arduino pin connected to the sensor's OUT pin.
const uint8_t sensorPin = 2;

void setup()
{
Serial.begin(115200);
}

void loop()
{
int16_t t = pulseIn(sensorPin, HIGH);

if (t == 0)
{
// pulseIn() did not detect the start of a pulse within 1 second.
Serial.println("timeout");
}
else if (t > 1850)
{
// No detection.
Serial.println(-1);
}
else
{
// Valid pulse width reading. Convert pulse width in microseconds to distance in millimeters.
int16_t d = (t - 1000) * 3 / 4;

// Limit minimum distance to 0.
if (d < 0) { d = 0; }

Serial.print(d);
Serial.println(" mm");
}
}

micro:bit MakeCode program for reading pulse width output

Pololu have also created a MakeCode example program for the BBC micro:bit single-board computer that demonstrates how to read and convert the output of the Pololu Distance Sensor with Pulse Width Output, 50cm Max. The program’s output can be viewed in the MakeCode device console, which also plots the readings on a graph. You can open the program in the micro:bit MakeCode editor by clicking this link.

Jumper settings (irs17a)

The board features four surface-mount configuration jumpers that determine its operation mode. Different versions of the Pololu Digital Distance Sensors ship with the appropriate jumpers pre-populated with 0 Ω resistors. These resistors can be desoldered from the populated spots or solder bridges can be added across the unpopulated spots to convert one sensor version into another. This sensor can be converted into any other irs17a version as listed in the following table.

Output type Sensor Maximum range Resolution Minimum update rate Jumper settings (4321)
digital
(does not provide distance measurement)		 POL-4050: Digital output, 5cm 5 cm - 145 Hz 0000
POL-4052: Digital output, 10cm 10 cm - 115 Hz 0010
POL-4054: Digital output, 15cm 15 cm - 95 Hz 0100
POL-4066: Digital output, 25cm 25 cm - 100 Hz 0000
POL-4067: Digital output, 50cm 50 cm - 100 Hz 0001
POL-4069: Digital output, 100cm 100 cm - 100 Hz 0011
POL-4077: Digital output, 200cm 200 cm - 30 Hz 1011
pulse width
(provides distance measurement)		 POL-4064: Pulse width output, 50cm max 50 cm 3 mm 50 Hz 1110
POL-4071: Pulse width output, 130cm max 130 cm 1 mm 100 Hz 0101
POL-4079: Pulse width output, 300cm max 300 cm 2 mm 30 Hz 1101