This compact sensor makes it possible to measure the distance of objects up to about 50 cm (20″) away using a simple digital pulse width interface (similar to a hobby servo control signal). 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 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.

A camera with no IR filter shows the infrared light emitted by a Pololu Digital Distance Sensor.

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

     d=3 mm4 µs⋅(t –1000 µs) ${\displaystyle d=\frac{3\text{\hspace{0.17em}mm}}{4\text{\hspace{0.17em}µs}}\cdot (t –1000\text{\hspace{0.17em}µs})}$

     t=1000 µs+4 µs3 mm⋅d ${\displaystyle t=1000\text{\hspace{0.17em}µs}+\frac{4\text{\hspace{0.17em}µs}}{3\text{\hspace{0.17em}mm}}\cdot d}$

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 1.667 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, depending on the proximity of the detected object.

The maximum detection range depends on object reflectivity and ambient lighting conditions. In our 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 to within about 5 mm of the sensor face, the effective minimum distance it can measure is around 1 cm, so objects closer than 1 cm might result in an inaccurate measurement.

Specifications