For 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.
[Sal] sent us his digital electric meter monitor, which immediately made us nostalgic for some of Forrest Mims’ books. Sal’s schematic and circuit description are similar to Forrest’s style, and we mean that as a compliment. Even in today’s world of CAD and EDS packages, sketching out a circuit by hand is sometimes both easier and faster. The schematic isn’t the only classic aspect of [Sal’s] design. He’s collecting data using a parallel port on an unused PC: in this case, a Toshiba Libretto running Windows 95. Before cheap flash-based microcontrollers and dev boards were available, the PC parallel port was the go-to hardware hacking interface for many of us. Plenty of the software running those old hacks was written in basic, and [Sal’s] meter is no exception. His software runs on Microsoft QBasic, which shipped with Windows 95.
The circuit takes advantage of the digital meter’s output: a 10 ms pulse for every 1 Wh of energy used. An IR photo detector from RadioShack detects the meter pulses, which are amplified by an LM324 Op Amp. An NPN transistor then shifts the output to send it to two 74LS73 JK flip flops. The first flip flop uses a transistor to drive an LED for visual output. The second JK flip flop sends the data to the PC. The flip flop has the effect of dividing the number of meter pulses by two, creating a much longer toggled signal that a PC can better detect.
Although using an AVR or PIC would consume less power, [Sal’s] setup has already more than paid for its power usage. By monitoring and adapting his electrical usage, [Sal] is saving $20 a month on his electric bill. We’ve included [Sal’s] circuit diagram and source code after the break (apologies to our readers on RSS).
Continue reading “Digital Electric Meter Monitor Goes Old School”
Cycling power meters can set you back quite a pretty penny. [Keith] quotes prices starting at $1500 and going up to $4000. We know several serious cyclists who would think twice about spending that on a bike, and wouldn’t even consider putting that kind of investment into an accessory for it. But if you’ve got the time [Keith] will show you how to build and install your own cycling power meter.
The link above is a roundup of all the posts and videos [Keith] made along the way. We’ve embedded his introduction video after the break where he discusses the goals of the project. The system allows for independently measuring the power of each leg. This is accomplished using strain gauges on the cranks to monitor torque. This data is combined with cadence measurements (how fast the rider is turning the cranks) which is all that is necessary to calculate the power output of the rider.
The parts list comes in at about $350. This doesn’t include the equipment he used to test and calibrate his calculations.
Continue reading “Build and install your own high-end cycling power meter”
[Dave’s] been elbow-deep in mains voltage while building this home energy monitoring rig. He started with an approach that is different from most we’ve seen before. He wanted a system that could make a linear measurement to keep the accuracy as high as possible. His first thought was to use a opto-isolated linear amplifier to measure voltage, but ended up altering that plan since he’s looking for digital values when all is said and done.
He’s using an ADC on the mains side of the interface board, then sending the digital values to an Arduino with opto-isolators to keep the high voltage separate from the low. This does complicate things a little bit, as he has low voltage rails on either side; 0V and 5V to run the ADC on the mains side, and separate 0V and 5V to run the Arduino. To solve the problem of accurate current measurement over the full range a house uses he opted for a Programmable Gain Amplifier. It’s addressed via SPI and allows him to adjust resolution to facilitate accurate measurement of very small currents. We think anyone who has tried to measure small appliances (like an alarm clock) with a Kill-A-Watt and gets a zero reading will appreciate this.
The Arduino sends data via a serial connection, which [Dave] is currently graphing using his laptop. It would be nice to see a simple web-server using the Ethernet shield (or a different board like the RPi) so you could log in from the couch and see what’s been going on with your home grid.
After years of hoping and wishing [Dave] finally took the plunge and installed solar panels on the roof of his house. He’s got twelve panels that are each rated at 240 Watts! But just having them sitting there and pumping power back to the grid isn’t enough. Understandably, he decided to add his own solar array monitor so that he could see just what those babies are bringing to the party.
The solar array has an inverter which takes the DC from the cells and converts it to mains voltage AC for use on the grid. The system includes a panel meter which you’d normally find on the supply to the house. All he needed to do is find a way to grab the data from that device. It’s an Elster meter, and offers two types of feedback: a blinking LED that corresponds to each Watt-hour passing through the meter, and an IrDA port which provides a more error-proof method of reading data. Monitoring the 1 Wh pulse is quite a popular method for keeping track of your electric meter, but if your hardware misses a pulse the data will be off. [Dave] chose to use a light sensor to monitor the IrDA output, which is encoded data. As long as you can read the protocol, which has been published by Elster, a transmission can be missed now and again without disturbing the overall power consumption data.
[Janne Mäntyharju] wanted to get an idea as to how much electricity he consumed in his new home, mainly to see if using his fireplace for additional heat had any effect on his bill. Luckily his power meter was mounted in the utility room of his house, making it easy to keep tabs on his usage.
His meter features a small LED that blinks a fixed number of times per consumed Kilowatt hour, so he mounted a photoresistor and ATtiny2313 above it to detect the light pulses. [Janne’s] server polls the microcontroller every 5 minutes over an XBee connection, recording the power usage in an SQL database for further analysis. From this database, he generates graphs showing both the temperature in his home as well as the average electricity usage for the specified time period.
[Janne] also wanted to make the data easily accessible, so he constructed a wall-mounted display using a Beagleboard and digital picture frame. The display not only shows his electricity usage, but it toggles between the weather, calendar events, IRC logs, and pictures from his security camera.
We’ve certainly seen this sort of electric meter monitoring before, but it serves as a quick reminder that given the right tools, watching your power usage (among other things) can be as easy as taking a quick glance over at the wall.
Apparently if you run AC and DC currents through a welding torch flame you can use the resulting plasma as a loudspeaker. [Thanks Cody]
The Google Power Meter API is no longer in development but that didn’t stop [Pyrofer] from finishing his metering hardware. It uses a reflectance sensor to read the meter instead of using clamp-based current sensing.
Music videos from inside the instrument
Filming from inside of a guitar creates the camera effect seen above which looks like the waveform you’d see on an oscilloscope. [Thanks Philleb]
Hidden messages in audio files
GhostCoder lets you encrypt and hide audio files within other audio files. The thought is, you can piggyback your own data into Torrents that are circling the interwebs.
If you’re skilled with a Skill saw you can make a chair out of one 2 by 4. You can see the pattern you’ll have to cut out from the board in the image above, wow!