ROBOTMAK3RS Blog

I mowed the lawn today. But we'll get back to that. I've had the chance to play with Dexter Industries new temperature sensors recently. These are thermistor-based, and read as analog sensors by the NXT. There are two versions: the "O" or open version, which is essentially a bare thermistor for a fast response, and a "P" or protected version that encloses the same thermistor in a stainless steel sheath. Rated from -50° to 150° C (-58° to 302° F) they span just about any (un)reasonable temperature a LEGO user is likely to need, from dry ice to the average oven (I'm pretty sure the plastic coating on the cord would not handle that; don't do it), and reasonable resolution which varies with temperature but is as fine as 0.15 °F (the resolution is poorer near the upper & lower extremes). Dexter Industries provides NXT-G blocks to read the sensors that work very nicely - under NXT-G 2.0, the block provides better than 1° F resolution, and will output...

MDP Dave Astolfo has published a review of a set of Dexter Industries Thermal Sensors and compared them to the LEGO® Education NXT Temperature Sensor. Have a look at the according page at www.plastibots.com .

For various reasons, LEGO only sells the temperature sensor through it's educational channel. That's fine... but how can the average user, with only the Retail software, use them? That's been a problem I've had a lot of folks email about, asking how I use it under NXT-G and if I can "share my secret". Well, how about Steve Hassenplug just hosts my secrets ? Look about half-way down this page, at the "Temperature Block" and the "I2C blocks" below it Inside the LEGO temperature sensor is a Texas Instruments chip (a TMP275 chip to be exact), which can be controlled like any other I2C device. That's handy, and there are 3rd party add-on blocks that will let you let you read a byte via I2C, or write a byte via I2C, or even read a series of bytes (multi-byte read) via I2C. Steve has also been kind enough to host copies of these right under the My Block I drew up to read the sensor. Note that you need to configure the sensor before reading it ...

I realized I have a lot of sensors. I should really review them :). I've been using the new NXT temperature sensor (mentioned here in the blog a while back) for a couple of projects, and decided to blog my opinion of it. Note this isn't even remotely authorized, approved, or perhaps even noticed by LEGO et. al... these are just my experience and opinions, your mileage may vary. Both the old analog temperature sensor ( product ID W979889 , $38.95, although you need a conversion cable to use it with the NXT) and the newer digital temperature sensor ( product ID W979749 , $39.95) are available from LEGO Education (they're not normally distributed through the retail arm of LEGO). I've been using these for a number of projects, including monitoring the temperature in my house and freezer, and recently for instrumenting a model geyser (in my kitchen... yeah, it's messy around here). The old sensor is analog - it actually put out a voltage that changed with the temperatur...

To see how NXT-2.0 and the new temp sensor performed, I ran the following test. (Click on the graphic for an enlarged view). 1) The bottom bar graph shows the temperature in our living room: 65.4 degrees Fahrenheit, proof of our extremely low natural gas consumption. (This has its downside, as you'll see from the next graph). 2) The middle graph shows the temp when my hand is wrapped around the temp sensor. (I didn't hold it long enough to actually warm it up, but 80 degrees Fahrenheit is a frighteningly low temperature for a body extremity). 3) The top graph shows the temp when the sensor is placed next to my body, underneath my shirt and fleece pullover. (It was only there for about 30 seconds, but an 87 degree body temperature indicates severe hypothermia--I'm heading for the fireplace). I did establish a Bluetooth connection with the new software and firmware, so the next step is to test remote data logging. I want to test the exportable MyBlocks feature as well. More l...

According to the creator, the reading range of the sensor was deliberately narrowed in order to conform to the limitations of the model's mechanism. More documentation and photos are here .

Here and here .