Review – Dexter Industries – DI Thermal Series Sensor Roundup (Updated)


I recently had the chance to test out a set of Dexter Industries Thermal Sensors produced for the NXT. For those that are not aware, Dexter Industries has entered the market of producing LEGO Mindstorms NXT-compatible sensors and has come up with some pretty cool ideas such as the dSwitch (allows you to switch in-home devices on/off using the NXT) and some cool new ideas such as solar charging for the NXT as well as a flex sensor (stay tuned for more on this).

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Reviews – Mindsensors Magnetic Compass

The folks at Mindsensors were kind enough to send me over this Magnetic Compass sensor to test. The sensor serves the useful task of providing the NXT with an indication of its heading angle from magnetic North to the NXT. It uses orthogonal two-axis magnetic sensor from Honeywell (HMC1052) and provides digital communication with NXT. Click the image below to see a video showing the compass in action. I did a brief test of this sensor and it worked as expected. More on this later…

Construction:
The sensor uses a standard NXT cable plug to interface the unit with the NXT. It is not encased in any plastic or bricks. Instead, it provides standard width Lego mounting holes to integrate with studded or studless beams and connectors.

Have a sensor or add-on that you want reviewed? Drop me a line.

Reviews – Mindsensors MotorMux

After building my original DominoBotNXT I was not happy with the need for it to backup each time a domnio was placed. (see link for details on this). The stanard NXT system provides only 3 motor ports. On DominoBotNXT, 2 were used for the drive wheels and 1 for the domino placement gate. This resulted in the need to tied the domino conveyor that carries each domino to the gate to be driven directly from the left drive wheel. When placing a domino, the distance between each was too wide, so it would have to back up each time one was placed. To fix this, I needed a 4th motor and a means to drive one. So, how do you do this with only 3 motor ports you ask??? Good question, I’m glad you asked as that is what this page is for….

The Motor Multiplexer from Mindsensors attaches to a single sensor port and allows the NXT to drive an additional 4 motors. In my case, I only needed 1. Using RobotC, I was abled to write (with some help from Dick Swan and Nitin Patil – thx guys) code that would allow communication with the IC2 interface on the sensor to control the 4th motor. So, in the programming environment, I simply had another motor port and use it in a similar way to the 3 core ports on the NXT. It only took a little bit of code to get this working. Now, DominoBotNXT can continue to drive forward while placing domino’s – making it much faster at its task. For info and a video on this, visit my DominoBotNXT2 page.

Results:
I am happy with the way this sensor works. I was working with a pre-production beta version that had some glitches (one port did not work), but I have been assured that the production units have this addressed.

Construction:
The sensor uses a standard NXT cable plug to interface the unit with the NXT. It is not encased in any plastic or bricks. Instead, it provides standard width Lego mounting holes to integrate with studded or studless beams and connectors.

Have a sensor or add-on that you want reviewed? Drop me a line.

Review – TechnoStuff PIR (Passive Infrared) Sensor

ne of my early Mindstorms projects was to build a fire extinguishing robot. I did this using the parts I had at the time. It was based on a walker platform and used a pneumatic circut to “blow” the fire out when detected. It worked reasonably well with the provided light sensor. Recently, I discovered the PIR (Passive Infrared Sensor) from TechnoStuff. This sensor was built to detect infrared heat and seemed to be a good fit for my next project. I mounted it to my new FireBot in tandem with a standard light sensor. Together, they would do the job of detecting a flame.

A candle was used as the “fire” in this project. The sensor was set as a Light Sensor:
SetSensorType(SENSOR_2, SENSOR_TYPE_LIGHT);

The code was straight forward.  When the sensor detects a value > 40, it “see’s” heat. In order to get accurate readings for this, it is recommended to take numerous readings (say once ever 20ms) and average them. This is to avoide variances in the sensor detecting other movement such as humans or other devices giving off infrared. As noted previously, the robot used both the PIR and a Light sensor together to detect the fire. By taking readings from both sensors and comparing their results to what would be expected when a flame is near, the robot was better able to detect the flame. To view the code, see the FireBot details page and download the source code.

Results:
The sensor worked well, but it is best to combine it with a light sensor. Together the two can be used to detect a fire or other object giving off infrared.

Construction:
The quality of the product both in workmanship and function is top notch.  It is obvious that Peter takes time and know-how when creating each one of these. The visual quality of the sensor may make you think that this one came from Lego themselves if it wern’t for the TechnoStuff logo on the side…

TechnoStuff Home Page

Review – TechnoStuff DIRPD Sensor – Review

One of the my challenges was to build a bot that could effectively avoid obstacles before it hit them.  My first attempt was to use the Lego Light sensor and the RCX to do this. The RCX would send out IR pulses and the Light Sensor would be used to read them and, based on how long they took to get back to the Light Sensor, could determine proximity. This worked realively well, with the exception that it was difficult to “tell” which side the robot should “look out” for… I came across a Dual Infra-Red Proximity Detector (DIRPD) that is currently being made and sold by Peter Sevcik. Once I received the unit, I went fast to work.  My plan was to build a robot in time for Christmas to deliver a set of diamond earnings to my fiance as well as test the abilities of this new sensor.  The bot depicted is a paired down version of the actual one that was used, but it still functions in the same way.

The sensor was set as a Light Sensor SetSensorType(SENSOR_2, SENSOR_TYPE_LIGHT); The code was straight forward.  The bot would drive forward until SENSOR_2 returned one of the following values:
0 Object in front.
22 Object on left
48 Object on right.
75 No object detected -continue
Based on those values, a decision would be made to turn in a specific direction.  I also added in some randomizing for when the bot met an object head on.

Results:
The sensor worked exceptionally well.  Reaction distance was predictable at approximately 16 to 24 inches.  I only stumbled across one minor issue.  The bot would have difficulties when approaching a standard doorway (i.e. bedroom) from the center.  Both left and right would trigger and the bot would get stuck trying to decide what to do.  This is easily fixed by building a routine that could detect this, make the assumption that it was a doorway, stop detecting, go through for x amount of time, and proceed with detection.  This is also proof that the sensor is doing exactly what it was designed to to.

Construction:
The quality of the product both in workmanship and function is top notch.  It is obvious that Peter takes time and know-how when creating each one of these. The visual quality of the sensor may make you think that this one came from Lego themselves if it wern’t for the TechnoStuff logo on the side…

Summary:
If you are looking for an effective, easy-to-use sensor for proximity detection, the DIRPD is it.  It is easy to mount, program, fairly priced and looks good too boot! Good work Peter.

Have a sensor or add-on that you want reviewed? Drop me a line.

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