Ceruleanplains.com - Amateur Robotics Project Journal

Sensor Subsystem

Purpose: the sensor system is the system concerned with instrumentation required to perform actions of estimation of the agent's position and direction as well as monitoring of health and status. This subsystem concerns itself with gathering the necessary information in order to enable the agent to have enough information to carry out it's mission as well as protect.

INFRARED VS. ULTRASONIC WHAT YOU SHOULD KNOW by airman00 28 January 2008

SENSORS - ROBOT SONAR by Admin

SCHEMATICS - INFRARED EMITTER DETECTOR by Admin

IR Emitter / Detector: From Andy Lindsay's Robotics with the Boe-bot

ROBOT SENSOR INTERPRETATION by Admin

LED TUTORIAL by Admin

LED: From Andy Lindsay's Robotics with the Boe-bot

COLOR SENSORS TUTORIAL by Admin

SENSORS - SHARP IR RANGE FINDER by Admin

SCHEMATICS - PHOTORESISTOR by Admin

Photoresistor: From Andy Lindsay's Robotics with the Boe-bot

ROBOT FORCE AND TORQUE SENSORS by Admin

SENSORS - ROBOT ENCODER (SLOT, ROTARY, LINEAR) by Admin

SENSORS - DIGITAL COMPASS by Admin

SENSORS - CURRENT SENSOR by Admin

SENSORS - ACCELEROMETER by Admin

PROGRAMMING - COMPUTER VISION TUTORIAL by Admin

SCHEMATICS - TACTILE BUMP SENSOR CIRCUIT by Admin

Whiskers: From Andy Lindsay's Robotics with the Boe-bot

MERCURY SWITCH TUTORIAL by Admin

Updates

Monday, March 31, 2008

Uploading some important links in the SoR tutorial vault and past SoR posts that I contributed a body of knowledge toward. I'll probably move the links to somewhere more helpful in the future.

In response to user "benji" on SocietyofRobots.com sharp IR 'radar' post on 29 March 2008

30 degree beams are useful when trying to track along long walls. you're mentioning the issue of beamwidth vs. precision.

For radars anyway... the 3dB precision is beamwidth = wavelength / diameter of the aperature
and for optics... beamwidth = 1.22 wavelength /diameter (note these formulas assume small beamwidths so a small angle assumption is played and the sine portion is often neglected). These formulas are valid for EM radiation.

Regardless... if the object you're looking for is less than this beamwidth, then you may need either a larger diameter aperature or use a smaller wavelength. Otherwise you're good. So if it's a vertically oriented pencil you're looking for, you might have some trouble finding its position precisely, but if it's a 5" wall... then you have a different story.

This location:
http://www.edgetech.com/pdf/App_Note_Beamwidth.pdf
Mentions a formula for apply beamwidth for sonar systems (not precisely ultrasonics - and I didn't validate it).

"benji" on SocietyofRobots.com sharp IR 'radar' post on 25 March 2008

"i dunno how the heck people map with ultrasonic
i read about it and it has a 30 degree beam
this thing is pretty unprecise,,
maybe they use some code tricks with it? im not sure about this one
i still believe tha ir is a better choice for mapping unless its range"

In response to user "Admin" on SocietyofRobots.com sharp IR 'radar' post on 20 February 2008

Perhaps the Sharp IR avoids the sunlight by using as its wavebands some of the areas of the solar emission spectrum that are absorbed by water vapor. .

While 47% of sunlight is in the near-ir (800nm-2600nm) most of it is before 1400nm. Even so there area a number of null areas that you can completely ignore the sun such as the 1800-2000nm range and 1350-1400nm. If your other sensor was in the 1000 range or 1600 range, I could see how it would freak out.

I attempted to review the Sharp IR data sheet for help, but didn't find anything of value for wavelength.

In response to user "Admin" on SocietyofRobots.com sharp IR 'radar' post on 2 March 2008

This my first post - so I hope this is helpful.

there's a few things you could do to mitigate the effects of the IR outside these three are increasing in difficulty and cost:

1.) you can put the sensor in a deep cavity (~2-4") with black absorbing material e.g. foam in a camera case surrounding it. this reduces scattering from the surroundings that would add noise to the detectors. this is highly fov constraining however. but you can have a linear array to increase this. the downside is that the black material in the sun will eventually heat and saturate the sensor.

2.) the IR from outside is also going to be because of the temperature differentials as well as the material backscatter in IR. you can test this as airman seems to be trying out; but all materials will have some backscatter and thermal mass to them. lighter materials will have different signatures than heavy materials. also color and reflectivity matter, so these characteristics will change the behavior from room temperature dynamics. This is because a lot of the sensors are likely using black or gray body assumptions for the temperature response unless they have multiple IR colors. so a near field background calibration is necessary often. this means you have a control that you look at at a controlled temperature and reflectivity and then you can try and compare those readings to what your sensor is observing in the real world. [cheap way is to possibly put this in a box in a specific area of the field of regard of the sensor and take some occasional measurements/cals]. adding a color sensor & photodetector could help.

3.) outdoors can have a lot of particulates and aerosols and more variation in water vapor than indoors. avoiding these variations is generally a good idea, or having active monitoring of these conditions to eliminate the biases to your readings. this again more advanced and will require a lot more sensors and more $.

basic rule is to eliminate the random backscatter, control or observe the thermal properties of the bot's sensors, calibrate out the noise, and rule out false alarms with other sensors.

"Admin" on SocietyofRobots.com sharp IR 'radar' post on 20 February 2008

"Despite popular belief, it is quite possible for both direct and indirect sunlight to significantly affect results.
I never tested it entirely, but I theorize direct sunlight can flood the sensors.
Maybe I'll do an experiment sometime and report back (but not now, busy on another project)."

Monday, February 11, 2008

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An astronautics engineer, the author is interested in studying artificial intelligence and more specifically the intelligent agents created to accomplish specific tasks. The goal of his projects are to build a robotics test bed for experimentation and discussion amongst peers.

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