The Sharp distance sensors are a popular choice for many projects that require accurate distance measurements. This IR sensor is more economical than sonar rangefinders, yet it provides much better performance than other IR alternatives. Interfacing to most microcontrollers is straightforward: the single analog output can be connected to an analog-to-digital converter for taking distance measurements, or the output can be connected to a comparator for threshold detection. The detection range of this version is approximately 10 cm to 80 cm (4″ to 32″).
The GP2Y0A21 uses a 3-pin JST connector that works with Pololu's 3-pin JST cables for Sharp distance sensors (not included), as shown in the upper picture on the right. These cables have 3-pin JST connectors on one end and are available with pre-crimped male pins, pre-crimped female pins, and with unterminated wires on the other end. It is also possible to solder three wires to the sensor where the connector pins are mounted (see the lower picture to the right). When looking at the back, the three connections from left to right are power, ground, and the output signal.
Pololu also carry an assortment of mounting brackets designed specifically for this sensor:
|Family of brackets for Sharp GP2Y0A02, GP2Y0A21, and GP2Y0A41 Distance Sensors.|
- Operating voltage: 4.5 V to 5.5 V
- Average current consumption: 30 mA (typical)
- Distance measuring range: 10 cm to 80 cm (4″ to 32″)
- Output type: analog voltage
- Output voltage differential over distance range: 1.9 V (typical)
- Update period: 38 ± 10 ms
- Size: 44.5 mm × 18.9 mm × 13.5 mm (1.75″ × 0.75″ × 0.53″)
- Weight: 3.5 g (0.12 oz)
Linearizing the output
The relationship between the sensor’s output voltage and the inverse of the measured distance is approximately linear over the sensor’s usable range. The GP2Y0A21YK datasheet (374k pdf) contains a plot of analog output voltage as a function of the inverse of distance to a reflective object. You can use this plot to convert the sensor output voltage to an approximate distance by constructing a best-fit line that relates the inverse of the output voltage (V) to distance (cm). In its simplest form, the linearizing equation can be that the distance to the reflective object is approximately equal to a constant scale factor (~27 V*cm) divided by the sensor’s output voltage. Adding a constant distance offset and modifying the scale factor can improve the fit of this line.
Alternative Sharp Distance Sensors
Pololu have a variety of Sharp distance sensors to choose from, including a shorter-range (4 – 30 cm) version and a longer-range (20 – 150 cm) version of this sensor. These analog distance sensors have similar packages and identical pin-outs, making it easy to swap one version for another should your application requirements change. Pololu also carry the newer Sharp GP2Y0A60SZ analog distance sensor (10 – 150 cm), which outperforms the other analog Sharp distance sensors in almost all respects, offering a low minimum detection distance, high maximum detection distance, wide 3 V output voltage differential, high 60 Hz sampling rate, operation down to 2.7 V, and optional enable control, all in a smaller package.
|Sharp GP2Y0A02YK0F Sensor 20-150cm (left) next to Pololu Carrier with Sharp GP2Y0A60SZLF Sensor 10-150cm (right).|
For short-range detection applications, we carry three digital Sharp distance sensors that have low minimum detection distances and a high 400 Hz update rate. They are available with a 5 cm, 10 cm, or 15 cm range and simply tell you if something is in their detection range, not how far away it is. They are smaller than the analog Sharp distance sensors and draw less current.
|A variety of Sharp distance sensors.|
Note: The GP2Y0A21YK0F model is a lead-free (RoHS-compliant) version of the Sharp GP2Y0A21 Distance Sensor. The manufacturer recommends you insert a bypass capacitor of 10 uF or more between Vcc and GND near this sensor to stabilize your power supply line.
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