This small lidar-based distance sensor reports the distance of objects up to about 300 cm (120″) away 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 of 300 cm is only achievable for high-reflectance objects in good ambient conditions. Lower-reflectivity targets or poor ambient conditions will reduce the maximum range.
This compact sensor makes it possible to measure the distance of objects up to about 300 cm (120″) 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 2 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:
``d = (4 text( mm)) / (1 text( µs)) * (t – 1000 text( µs))``
``t = 1000 text( µs) + (1 text( µs)) / (4 text( mm)) * 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 300 cm will produce a 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 30 ms to 33 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 wall out to around 300 cm away, a white sheet of paper out to around 170 cm, and a hand out to around 100 cm. The following graph shows the measured distances of three units versus their actual distances from a variety of targets at several different ranges:
Please note that while this sensor can detect objects to within about 1 mm of the sensor face, the effective minimum distance it can measure is around 4 cm, so objects closer than 4 cm might result in an inaccurate measurement.Specifications
- Operating voltage: 3.0 V to 5.5 V
- Current consumption: 30 mA (typical) when enabled, 0.4 mA when disabled
- Maximum range: approximately 300 cm (120″) (for high-reflectivity targets in good ambient conditions; lower-reflectivity targets or poor ambient conditions will reduce the maximum detection range)
- Minimum range: 4 cm (for accurate measurement); < 1 mm (for detection)
- Update rate: 30 Hz to 33 Hz (33 ms to 30 ms period)
- Field of view (FOV): 15° typical; can vary with object reflectance and ambient conditions
- Output type: digital pulse width
- Dimensions: 0.85″ × 0.35″ × 0.136″ (21.6 × 8.9 × 3.5 mm); see the dimension diagram (193k pdf) for more information
- Weight: 0.014 oz (0.4 g)
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 neighbouring surface-mount pad on the back side labelled “EN” on the silkscreen. The ENABLE pin is pulled up to VIN, enabling the sensor by default.
The board has one mounting hole intended for use with #2 or M2 screws.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. (For more information about how the different output types work, see the product pages for representative versions.)
The output graph is a bit different for the versions that use a pulse width to encode the measured distance. The output for these versions is similar to hobby servo control signals and is shown below as a function of time.