A Motion Activated AC Switching Circuit Using Mostly Discrete Components

June 15, 2014 by Rick Osgood 17 Comments

AC motion switch

If you’ve ever dealt with a brightly lit Christmas tree, you might understand the frustration of having to crawl underneath the tree to turn the lights on and off. [brmarcum] feel’s your pain. He’s developed his own motion activated AC switching circuit to turn the lights on and off automatically. A motion sensor ensures that the lights are only on when there are people around to actually see the lights. The circuit also has an adjustable timer so [brmarcum] can change the length of time that the lights stay on.

The project is split into several different pieces. This makes the building and debugging of the circuit easier. The mains power is first run through a transformer to lower the voltage by a factor of 10. What remains is then filtered and regulated to 9VDC. [brmarcum] is using a Parallax PIR sensor which requires 4.5V. Therefore, the 9V signal is then lowered once more using a voltage divider circuit.

When the PIR sensor is triggered, it activates the timer circuit. The timer circuit is driven by a 555 timer. The circuit itself was originally borrowed from a classic Forrest Mims book, though it was slightly modified to accommodate the PIR sensor. The original push-button trigger was removed and replaced with the signal from the PIR sensor. The only problem is that the circuit was expecting a low signal as the trigger and the PIR sensor outputs a high signal. [brmarcum] resolved this problem with an NPN BJT to invert the signal. Once the timer is triggered, it flips on a relay that allows the mains electricity to flow through to the lights.

[brmarcum] soldered the entire circuit onto a piece of protoboard. The final product was then mounted securely inside of an insulated plastic case. This allows him to mount the circuit safely underneath the Christmas tree skirt. The PIR sensor is kept external to the enclosure and wired up into the tree itself. This allows the sensor to still detect motion in the room while the rest of the circuit is hidden away.

[via Reddit]

First Stab At Motion Sensor To Disconnect A Car Charger

March 24, 2014 by Mike Szczys 108 Comments

motion-sensing-car-charger

[Pixel] just sent in this automotive hack which disconnects his car charger when the vehicle stops moving for at least 10 minutes. Why would you need such a thing? The 12V outlet in his vehicle isn’t disconnected when the ignition is turned off. If he leaves a charger plugged in when parking the car, he often returns to a drained battery.

The fritzing diagram tells the story of this hack. He’s using a 7805 to power the Arduino mini. This monitors an ADXL362 accelerometer, starting the countdown when motion is no longer sensed by that chip. At the 10-minute mark the N-channel MOSFET kills the ground side of the outlet. Good for [Pixel] for including a resetable fuse on the hot side. But it was the diode all the way to the left that caught our eye. Turns out this is part of a filtering circuit recommended in a forum post. It’s a Zener that serves as a Transient-Voltage-Suppression diode.

Another comment on that thread brings up the issue we also noticed. The 7805 linear regulator is constantly powered. Do you think putting the uC into sleep and leaving the linear regulator connected is an adequate solution? If not, what would you do differently?

SenseLamp Automates Rooms By Replacing Light Fixtures

April 2, 2013 by Mike Szczys 25 Comments

senselamp

Would you believe that this beautiful light fixture is actually a hacked together home automation project? Okay, so this wire mess is the second of three versions that [Christian] built. It replaces a light fixture in the room, but if you look closely you’ll see that there is a compact fluorescent bulb included in the build. The laser-cut frame acts as a bit of a lamp shade, while providing a place to mount the rest of the hardware.

The final version cleans things up a bit, and adds a footprint for the PIR motion sensor that he forgot to design into this version. The idea is that each lamp monitors motion in the room, switching the light on and off again as necessary. A light-dependent resistor ensures that the bulb is only powered up if the room is dark so as not to waste electricity during the day.

The build includes a sensor package that reports back temperature and humidity data. Communications are provided by a WR703N router rolled into each of the four units installed in his house. With this kind of hardware at his disposal it should be a snap to control every IR remote control device in his house via the network by adding an IR LED and some code to the lamps.

An Umbrella Stand That Tells You The Weather Forecast

November 15, 2012 by Mike Szczys 9 Comments

This project takes an umbrella stand and gives it the ability to let you know if you need to take an umbrella when you leave the house. The image above is a concept drawing, but a first prototype was built and seems to work quite well. See for yourself in the video after the break.

The project was put together by openPicus. They sell a prototyping module called the Flyport which provides a WiFi connection to your projects. This board connects to a set of LEDs which are used to illuminate the translucent plastic umbrella stand. But you might not notice the color change if the LEDs were always on. Also designed into the system is a PIR motion sensor. When you walk toward the door to leave for the day it switches on the appropriate color — green for clear, blue for raining, and red for storming — catching your attention in time to grab an umbrella as you pass by.

You don’t need to spend a bundle to pull off a hack like this. You can scavenge for a PIR sensor, use one color of LEDs just to tell you when rain or storms are forecast, and an ENC28J60 is a cheap and easy Ethernet alternative to using WiFi.

Continue reading “An Umbrella Stand That Tells You The Weather Forecast” →

Dual PIR Photo Trigger By Crossing The Streams

August 3, 2012 by Mike Szczys 9 Comments

Motion sensing can be quite effective when taking photographs of wildlife. But how can one be sure that the motion was at the center of the frame? A PIR sensor picks up motion in its entire viewing range. It’s not really something that can be aimed. But if you use two PIR sensors you can monitor a focused area for motion.

The trick is to use a logic circuit. By building an AND gate you can trigger based on motion in the area which is overlapped by both of the sensors. In this case the AND gate is built from a voltage divider. The outputs of the PIR sensors are connected above and below the divider’s connection to the photo trigger. Both have a protection diode, and the divider is tuned so that both PIR outputs must come one in order to raise the trigger input above the voltage threshold. So much for never crossing the streams.

[via TriggerTrap]

Are You Smarter Than A Raccoon?

June 22, 2012 by Mike Szczys 63 Comments

[Ben] has a raccoon problem. It seems that it’s not uncommon for him to come face-to-face with a pesky raccoon in the middle of the night, in his living room. We think most people would solve the problem by preventing the raccoon from entering the home. But [Ben] just seems hell-bent on catching him. Most recently he’s added motion-sensing to a live trap which he installed…. in his living room.

So [Ben] has cat’s which that to roam at night. They have free range thanks to a cat door which the hungry pest has been exploiting. Apparently the masked robber has a taste for cat food and that’s what keeps him coming back. [Ben] has been using the cat dish as bait but up to this point the live trap hasn’t worked. You see the raccoon isn’t going inside to get the food, but reaches through the cage and pulls pieces out one at a time. The solution is to put up a solid surface around the cage, and hope that the motion sensor will get him this time. Although we’ve linked the most recent post above, you’ll want to page through his blog for the whole story.

Wouldn’t it be better to install some kind of automatic lock that only lets in the kitty?

Continue reading “Are You Smarter Than A Raccoon?” →

Pee-light Gives Guidance For Nocturnal Tinkles

December 14, 2011 by Mike Szczys 38 Comments

This light is a rather dim LED module whose purpose is to give you a very small bit of illumination when using the restroom at night. If you rely on it instead of using the overhead lighting in the bathroom, you’ll be able to find your way back to bed with your night-vision undisturbed.

[Fred] built the project as a way to learn more about using MSP430 microcontrollers. The protoboard seen above has a pair of female pin headers designed to accept an MSP430-PIR board, which uses the low-power microcontroller to monitor a PIR motion sensor. The chip can be reprogrammed and [Fred] did just that, using the USB dongle side of the eZ430-F2013 dev stick. Now when the sensor detects motion the chip first checks the light-dependent resistor on the protoboard to see if it’s dark in the bathroom. If so, it switches on the LED and sets a timer to shut if off again.

The system runs on a 9V battery, which is a bit under-powered for the 12V-spec’ed LED module. But [Fred] says the light it produces is just the right intensity.

[Thanks Jeremy]