distance alarm

Pierce

Does anyone know where I should begin to experiment with a distance alarm? I am trying to make a device that when your more than a certain distance from it an alarm goes off.

Mike Green

The BoeBot uses infrared for detecting the distance to objects like walls. There's also a version that uses a PING ultrasonic distance sensor to measure the distance to objects. Have a look at the PING documentation and examples (there are links on the product page: www.parallax.com/detail.asp?product_id=28015). Also have a look at the Robotics with the BoeBot tutorial (link here: www.parallax.com/detail.asp?product_id=28154).

Pierce

Thank you!

LoopyByteloose

There are a couple of dilemmas. Try out the different technologies to get a good idea of what works for you.

IR response will vary with the color and texture of the item detected. In some cases, the Ir just cannot reflect an item. It works best with identifying a consistent surface feature and consistent color.

Ultrasound can do better at identifying almost anything, but distance measurements may vary due to humidity or air currents.

PIR devices actually can sense the presence of body heat at a distance, but are no good on cold objects.

Of course, the closer you are, the better they all respond.

Video is another choice that can actually do much more sophisticated recognition. It can use a simple video image with color or IR imagining. The problem with video is that you have to learn a lot about both the hardware and the software.

And, a combination of two or more really improves accuracy by confirming data.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"Everything in the world is purchased by labour; and our passions are the only causes of labor." -- David·Hume (1711-76)········

···················· Tropically,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan

Chris Savage

To clarifications to Kramer’s post…Just so you know the pros/cons…IR reliability is reduced by bright ambient light, especially direct sunlight. IR has trouble with flat black colored objects because they absorb rather than reflect IR light. White objects work better. Ultrasonic sensors, such as the PING))) work well in most cases but also have two possible weaknesses. One is that soft material may not reflect the sound. So people/clothing are not good reflectors of sound. Also surfaces that are not perpendicular to the PING))) emitters don’t reflect as good, and depending on the angle may not reflect at all. I hope this helps. Take care.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Chris Savage
Parallax Tech Support