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ECE 445 Wiki : Topics : Sensors



Laser Diode and Photodiode Introduction : Introductory information to give students a jump start in design characteristics for laser diodes and photodiodes.

Charles Ruiz and KanKan Yu, 15 December 2006

Robotic Ultrasonic Sensors
Sensors are one of the most important components in robotics. It is what enables the microcontroller to interact with the outside environment. Different types of sensors are applied regarding to different applications, and one of the most common types is the range sensors. Range sensors not only allow the microcontrollers to “see” various objects, but often the various distance of the objects as well.

So which type of range sensors do you need for your application? For educational, nonprofessional, and sometimes even professional robotics, where industrial-grade precision is often not required, commercial sensors sold by the regular electronic companies provides decent and much more inexpensive options. Two types of range sensors are generally used: infrared range sensors and ultrasonic range sensors.

Ultrasonic Range Sensors

Ultrasonic range sensors use built-in transducer to generate short pulses of ultrasonic beams propagating out of the sensors, which are then reflected from any obstacle alone the beam path. The same transducer circuit at the same time shifts itself from pulse generation mode into pulse detection mode. The distance of the obstacle is then calculated based on the time elapsed between the generation and the detection of the beam. The most distinguished difference between ultrasonic range sensors and infrared range sensors is the beam width, and therefore the obstacle detection width. The light beams of the infrared sensors are usually very narrow compared to ultrasonic sensors, which provides wider beams based on the size of the transducer of the given ultrasonic sensor. Therefore, if your application requires detection of obstacles in a wider area, then the ultrasonic range sensors will be a better option than the regular infrared sensors.

MaxSonar Ultrasonic Sensors

The most commonly used ultrasonic sensors in nonprofessional robotics are the series of MaxSonar Ultrasonic Sensors provided by MaxBotix. The product line ranges from EZ0 to EZ4, each differs only with its beam width. The specific comparisons can be found Here.

MaxSonar EZ0 : datasheet

MaxSonar EZ1 : datasheet

MaxSonar EZ2 : datasheet

MaxSonar EZ3 : datasheet

MaxSonar EZ4 : datasheet

The MaxSonar Sensors come with seven connection holes. You’ll either have to tie wires onto the holes or solder the wires onto the holes to get the connection. If you’re only using the MaxSonar Sensors for regular obstacle detections, you’ll only have to connect your wires to three out of the seven holes. The rest of the holes have their own fancy purposes which will not be discussed here. The three holes are GND, +5V, and AN. While GND and +5V are self-explanatory, AN is the analog voltage output of the sensors. It uses an equation to output analog voltage based on the distance of the obstacle:

  VAN = ( VCC / 512 ) × distance(in)

So for example, if the obstacle is placed 1m away from the sensor, which is approximately 39.37inch, you’ll get a voltage reading from AN of roughly 384.47mV. Conversely, if your microcontroller reads an 384.47mV from the AN, then you know your obstacle is approximately a meter away from your sensor.

One very, very important note about the MaxBotix Sensors: they are very fragile!!! Since they are cost-efficient, non-industrial-grade sensors, there aren’t any built-in circuit protections. Which means, As soon as you accidentally hook up the GND and +5V in the reverse manner, smoke comes out, and the sensor blows (no explosion, just simply wasted).

The fastest and the cheapest way to purchase the MaxSonar sensors is to call the company directly. Remember to mention you’re a student, and you’ll get discount that makes the final price much cheaper than you can get from any other robotics supply websites.

Joe Meng, 15 December 2007

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