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A Motion Activated AC Switching Circuit using Mostly Discrete Components

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]

Do You Have Any Idea How Fast Your Blender Was Going?

blenderSpeed Some people really love their smoothies. We mean really, really, love smoothies and everything about making them, especially the blenders. [Adam] is a big fan of blenders, and wanted to verify that his Vitamix blenders ran as fast as the manufacturer claimed. So he built not one, but two speed measuring setups. Scientific blender measurement method requires one to cross check their results to be sure, right?

Measuring the speed of a blender is all about the RPM. Appropriately, [Adam's] first measurement tool was an LED based stroboscope. Stroboscopes have been around for hundreds of years, and are a great way to measure how fast an object is rotating. Just adjust the speed of a flashing light until the rotating object appears frozen. The number of blinks per second is then equal to the Rotations Per Second (RPS) of the object being measured.Multiply by 60 seconds, and you’ve got RPM. [Adam] used an Arduino as the brains behind his stroboscope. He wired a dial up on his breadboard, and used it to adjust the flash rate of an LED. Since this was a quick hack, [Adam] skipped the display and just used the Arduino’s USB output to display speed measurements on his laptop.

There are possibilities for error with stroboscopes. [Adam] discovered that if the stroboscope was flashing at a multiple of the blade’s rotation speed, the blades would appear frozen, and he’d get an erroneous RPM value. Thankfully, [Adam's] Vitamix had asymmetric blades, which made the test a bit easier. He calculated his blades to be spinning at 380 RPS, or 23,000 RPM. Not satisfied with his results, [Adam] brought out Audacity, and ran a spectral analysis of the blender in operation. He found a peak at 378Hz, which was pretty darn close to his previous measurement. Since the blender has a 4 inch blade this all works out to a blade tip speed right around the claimed value of 270 MPH. We’re glad [Adam] found an answer to his blender questions, but our personal favorite blender hack still has to be the V8 blender created by the Top Gear crew.   [via HackerNews]

DIY Coffee Maker Filters Out Manufacturer Specificity

Coffeemaker made from 3D-printed parts and scrap aluminium

This DIY electric coffeemaker prototype uses an assemblage of 3D-printed parts and cast aluminium. [siemenc]‘s main goal with this project was to utilize and demonstrate recycling and re-usability. He used Filabot filament exclusively and melted down scrap aluminium such as cans, foil, and CNC mill waste in an oven he fashioned from an old fire extinguisher. He also cast the aluminium parts himself from 3D-printed positives.

Of course, he had to buy the things that make this a coffeemaker such as the hoses, the fuse, and the heating element. If you’re wondering why he didn’t salvage these parts from yard sale machinery, it’s because he wanted to be able to replace any part of it and have it last as long as he needs it to last. The innards he used are not specific to any model, so he should be able to easily find a replacement.

Just like a pour over set up, [siemenc] has fine control over the strength and quantity of the brew. We particularly like this machine’s exotic bird looks as well; it may be a prototype, but it’s quite stylish. If you’re looking to go all the way with DIY coffee, why not grow your own beans and then roast the beans yourself?


HAL is Duct Tape for Home Automation

HAL Home Automation

When it comes to home automation, there are a lot of different products out there that all do different things. Many of them are made by different companies, and they don’t often play very well together. This frustration ultimately led [Daniel] to develop his own Python based middleware solution to get these various components to work as a single cohesive system. What exactly did [Daniel] want to control?

First up was the door lock. [Daniel] lives in an apartment building, so there are actually two locks. First, a visitor must be allowed into the building by pressing a button on the intercom system in the apartment. Second, the apartment door has its own dead bolt lock that needs to be opened and closed. [Daniel] was able to control the building’s front door using just a transistor hooked up to an Arduino to simulate the press of the physical button. The original button remains in tact so [Daniel] can still easily “buzz” in a visitor.

The apartment’s dead bolt was a bit trickier. There are off-the-shelf solutions to control a dead bolt, but they are often expensive. [Daniel] built his own solution using a simple servo motor bolted to the door. The servo is controlled by the Arduino which is in turn controlled via two broken intercom buttons that already existed within the apartment. The buttons were originally used to either speak to or listen to a visitor before buzzing them into the building. They had never worked for [Daniel] so he re-purposed them for his own project. The whole DIY door locker is enclosed in a custom-made laser cut wooden box.

Click past the break for the rest of [Daniel's] story.

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A Smart Clothes Dryer

dryer6 Here’s a question that will rack your brain: does your clothes dryer stop when the clothes are dry? It seems if you have a machine that guzzles power for one single purpose, you’d like it to stop when its job is done, or for the sake of convenience, keep going until the clothes are dry. Temperature and humidity sensors are cheap, and if you don’t have an auto sensing clothes dryer, a DIY smart clothes dryer seems both efficient and convenient.

[Andy] figured when clothes are dry, they stop emitting moisture. Based on that premise, he could monitor the operation of a clothes dryer and either shut off the machine or send a message that it’s time to take the clothes out. It’s a simple enough idea, and with an Arduino and a DHT11 temperature and humidity sensor, it was pretty easy to put together.

The clothes dryer used for this experiment was a self-ventilating model that doesn’t vent to the outside. Instead, it condenses the water in your towels and jeans into a tub to be emptied by hand later. This might introduce a little error into tests, but [Andy] did come up with a way to mount the temperature sensor without modifying his dryer in any way. From the initial data, the ventless dryer might be introducing a little experimental error, but it’s still too good of an idea to not try out with a traditional dryer that vents to the outside. Here’s the code should you want to try this yourself.

A WiFi Home Power Meter

acFor his masters at Cornell, [Christopher McNally] designed a simple, non intrusive home power meter capable of doing everything a ‘smart meter’ can do – log power consumption throughout a home, and display a log of a home’s power consumption over WiFi. He’s even testing out some interesting ideas, like automatically detecting when specific devices turn on by reading the current data.

From [Chris]‘[Jeramy] developed his system around the Arduino and a Ethernet shield, taking care of networking and choosing a micro, leaving him more time to develop the more interesting part of the project: sensing current. For this he used a small, clip-on current transducer. This sensor generates up to 10 VAC across a resistor, but the Arduino doesn’t play well with AC, requiring a small rectifier built around an op amp.

While the project works as a homebrew smart meter, [Jeramy] wasn’t able to automatically detect when certain devices were powered on. This is partly due to the fact that changes in current were only seen in magnitude and not waveform. Also, if two devices were powered on at the same time, the software would see that as a larger device that draws the sum of the current of two smaller devices. Still, [Jeramy] came up with a cheap way of metering power in any home, and the cost of his solution is cheaper than a lot of professional systems out there.

All the code, files, and design report are available on [Jeramy]‘ git.

A Low Cost, Solar-Powered Swamp Cooler


A looming, torturous summer is preparing to bear down on many of us, making this dirt-cheap swamp cooler build an attractive hack to fend off the heat.

Though this is a pretty standard evaporative cooler, the design comes together in a tidy and transportable finished product. The base is a ~$3, 5-gallon bucket from a local hardware store with its accompanying Styrofoam liner. Three 2 1/8″ holes carved into the side of both the bucket and liner will snugly fit some inch-and-a-half PVC pipe with no need for glue.

One last cut into the lid to seat a small desk fan rounds off this build—or you can chop into the styrofoam liner’s lid if you prefer. The video demonstrates using a 15W solar panel to run the fan, and we have to admit that the cooler seems to be an excellent low-cost build. It does, however, require a frozen gallon jug inside to pump out the chilled air for around 5-6 hours per jug. Maybe one of our frugal and mathematically-inclined readers can throw out some guesstimations for the cost of stocking the bucket with a jug of frozen water a couple times a day? Video after the jump.

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