Building A Battery-powered Motion Alarm

September 27, 2011 by Mike Szczys 15 Comments

[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.

Motion Activated Monitor Wakeup

February 21, 2011 by Mike Szczys 15 Comments

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]

Motion Sensing Light Module

May 2, 2010 by Mike Szczys 5 Comments

[Muris] is pumping out the home lighting hacks. He developed this motion sensing module as an add-on to the IR switch we saw last week. There’s some kind of fuse box above his entry door and its white cover, which you see above, is where he mounted an IR distance sensor to detect movement and switch on the lights. The RC5 infrared protocol is used to transmit the necessary signal to turn the lights on, then when a set amount of time has passed it will turn them back off again.