Building a battery-powered motion alarm

[Brad] was asked by his Sister to design a motion-based alarm that would help her catch her son sneaking out of the house at night. Obviously this didn’t need to be a long-term installation so he decided to throw something together that is only active at night and can be battery-powered. What he came up with is a light-sensitive motion sensor that uses very little power.

He knew that an Arduino would be overkill, and decided to try his hand at using the Arduino to develop code for an ATtiny85. It has an external interrupt pin connected to the output of the PIR module, which triggers action when motion is detected. The first thing it does is to check the photoresistor via the ADC. If light levels are low enough, the buzzer will be sounded. [Brad] measured the current consumption of his circuit and was not happy to find it draws about 2.5 mA at idle. He spent some time teaching himself about the sleep functions of the AVR chips and was able reduce that to about 500-600 uA when in sleep mode. Now all he has to do is find a nice place behind the house to mount the alarm and there’ll be no more sneaking around at night.

If you’re trying to keep a tight leash on your own kids you could always make them punch the time clock.

Automated hose keeps cats from watering you

Commenter [TheCreator] reminded us of this fantastic video from [Craig Turner] who you may recognize from SBS’s Top Gear Australia Video Competition.  You see, [Craig] has been struggling for some time with the problem of neighborhood cats relieving themselves pretty much all over his stuff. Through surveillance he identified (and named) around 9 separate cats sauntering into his yard during the wee hours of the night.  The only issue now was to humanely discourage them from entering his yard.

The best solution, in this case, was a simple spray from the garden hose, but who is going to stay up all night to watch for cats? [Craig]’s ’75 Galant happens to have aftermarket door locks. These typically contain a simple powerful 12V actuator that will push or pull when given current. The actuator is strong enough, and has enough travel, to depress your typical garden sprayer handle. The lock actuators even include enough mounting hardware to tack everything together.  The only irreversible part of the hack appears to be the hole drilled into the sprayer’s handle.

The job of cat detection is handled with a PIR sensor (sourced from his home security system) and a paper towel tube to narrow the detector’s field of view. Placed at animal height the PIR detector works like a trip line, and flips a relay connected to an array of devices:  A bright LED lamp, a DSLR set to take several quick photos of the victim, An HD video camera, and the sprayer solenoid.  This whole rig is placed at a convenient choke point and hilarity ensues! A schematic is included in the video but is pretty difficult to interpret, we transcribed it for you. Some details are unclear but essentially a few relays are stapled together to provide either high or low switching signals.

Check out the video, [Craig]’s schematic, and our interpretation of [Craig]’s schematic after the jump!

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Motion activated monitor wakeup

This hardware is used to keep a computer monitor awake when there is motion in the room. The monitor displays important information for firefighter in the vehicle bay, but only needs to be on when they are getting ready to go out on a call. The solution is a simple one, a PIR sensor combines with a mouse for motion sensitive input. When the PIR sensor detects motion it causes a mouse button click via a 2N3904 transistor. Now the monitor will not waste power or have burn-in over the long term, but whenever someone is in the room it will be displaying the information that the emergency workers need to know.

[Thanks Andy]

Today’s Arduino Minute

Sometimes projects are vast, complicated, and complex. Other times projects are a bit more on the simple. Today we thought we would share a couple projects with something in common that may be familiar sounding to the more experienced crowd, but may inspire a few readers new to the world of microcontrollers.

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German engineering produces an overcomplicated scarecrow

This electronic scarecrow keeps the birds away and makes your neighbors hate you at the same time. That’s because its way too loud, even if the next house is far away. The conrad.de folks that brought us the climbing bike storage device are at it again, putting together car audio and strings of lights as part of the bird-shoo-ing technology. In the video after the break you’ll see that they’re using a PIR motion sensor to switch power to an automotive amp and head unit. The speakers, strings of lights, and spinning doo-dads are all hidden under a black cape. When an unsuspecting bird tries to feast on the crops, the scarecrow unfolds its arm Dracula-style and raises a ruckus. We don’t expect to see this at a local farm, but maybe for next Halloween?

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Motion activated wildlife camera (or a spy device)

Now you can capture pictures of our furry friends by building a motion activated wildlife camera. [Doug Paradis] took his Air Freshener hack and used it to trigger a camera. The white dome in the picture above is the PIR sensor from an Air Wick Freshmatic, along with a cheap keychain camera and an MSP430 microcontroller. He used one of the chips that came with the TI Launchpad, a transistor, and some discreet components to interface the devices and then put them into a project box. Now he’s got a fully configurable motion-sensing camera.

Gutting an air freshener for the parts

[Doug Paradis] took a good look inside the Air Wick Freshmatic Compact i-Motion and then stole all the parts for other projects. We’ve looked at adding a manual spray button or making air fresheners Internet enabled before. Those models didn’t have parts that were all that interesting, but this one has a passive infrared motion sensor. You’ll also gain three switches, a PNP transistor, and an LED.

Price seems to be all over the map for this model, but [Doug] says you can find it for $8 or less. After showing how to make a tool to bypass the triangular security screws, he explains how to access the PIR sensor. But if you want to be all you can be with the hardware, he details the modifications needed to patch into the analog and digital circuitry on the rest of the board too.