High-Tech LEGO Chapter 7: Videos and Additional Sensors
Chapter 7 of High-Tech LEGO builds a Doppler radar sensor for detecting motion, as shown in the videos below. A benefit of this sensor is that it can see through solid objects. Further down on the page are examples of building other sensors, using the same technique described in Chapter 7.
The radar works by detecting motion, here from my hand in motion.
As shown here, motion can be detected through cardboard and wood.
Detecting motion through a door is useful, noting that the alarm sounds as it detects motion through the door before the door opens. The radar works well through wood, fiberglass, or glass. But one of the doors I tested was made with aluminum--the radar does not work through metal.
This video shows a force sensor. The sensing device creates and analog signal voltage that is proportional to the force applied. The EV3 Intelligent Brick has been programmed to create a tone of frequency corresponding to the amount of force.
Here's another example of a flammable gas sensor, which senses the presence of gases such as butane and propane. The EV3 Intelligent Brick has been programmed to create a tone of frequency corresponding to the amount of these gases.