Detecting Seismic Waves With A Piezo Element

December 11, 2011 by Mike Nathan 14 Comments

While we normally see piezo elements being used to output audio, [Veedo] thought that they could be used in a more useful manner. He bought way too many piezo film tabs and decided to use them to build a makeshift seismic sensor.

The piezo tabs came with weights attached at one end, though while testing them, he found that they more or less only detected vibrations with frequencies in the KHz range. Since earthquakes tend to produce vibrations in the 30-80 Hz range, he had to tweak his setup to detect the proper frequencies. To do this, he attached a weight made of a screw and washers, checking the output signals on his oscilloscope until the dominant sensed frequencies were in the range of 40 Hz.

The sensor was attached to a breadboard, then wired through a charge amp to create a small AC signal, which floats on 2.5Vdc. The bottom half of the wave is chopped off with a diode, after which it is fed into an Arduino Mega. The seismic data is then pushed up to his Pachube account for storage, though he can view the feeds locally via the a web server programmed into the Arduino.

We’re not sure how much advanced notice this sort of setup would give you in the event of an earthquake, but it seems like a fun project to build either way.

Buzzer Project For Classroom Team Games

December 9, 2011 by Mike Szczys 6 Comments

Want to host a Jeopardy tournament with your friends? Looking to add a bit more fairness to your school’s knowledge bowl? Perhaps you should build some buzz-in hardware of your own.

Here you can see [Matt Hanson’s] take on this idea. He used one Arduino to gather not just buzzer info, but also keypad data from four satellite controllers. Each has an RJ45 jack, allowing it to connect tot he base unit with an Ethernet patch cable. We like the color coding that [Matt] chose, which matches the color of the arcade button to the keystone jack on the base. And of course the fantastic look of the water-jet cut cases isn’t lost on us either.

You may wonder why he included a key pad on each controller? It looks like he and a few others worked together to develop a team-based math game for use in school.

Color Sensing With An RGB LED And Photoresistor

December 8, 2011 by Mike Szczys 11 Comments

[Fjord Carver] brings together an RGB LED and CdS Photoresistor to make a color sensor. Those Cadmium Sulfide lights sensors usually have a very wide swing of resistance when exposed to varying levels of light sensitivity. That makes for great resolution when reading them using the ADC of a microcontroller. The LED comes into play by shining known wavelengths of light on the surface being measured. Three separate readings are taken with each of the LED’s different colors, then used to extrapolate the RGB value of the test material. We saw the very same method used a couple of years back. This time around it’s an Arduino doing the measuring instead of a PIC.

So why isn’t that sensor shown in this picture? It’s because we appreciate the application which [Fjord] is using for this sensor. He built a lamp that shines the same color as the surface on which it is placed.

Christmas Tree Water Sensor Gets An Upgrade And A Fancy New Box

December 7, 2011 by Mike Nathan 9 Comments

xmas-tree-water-sensor

[Eric Ayars] has a nice cast iron Christmas tree stand at home, but the only drawback is that the stand makes it hard to see just how much water is available to the tree. Last year we covered a small gadget he created to help keep tabs on the water level, but as several of you predicted, the system eventually failed.

His previous solution used copper plated proto board to sense how much water was in the stand, but the leads corroded in about a week’s time. With Christmas just around the corner, he decided to give things another try.

His revamped water level sensor relies on measuring capacitance changes in a copper strip board when under water rather than detecting a complete circuit like the previous model. To protect his sensor this time around he coated the board with polyurethane, which should provide a decent corrosion barrier.

Using the Arduino CapSense library, the sensor can detect the presence of water, signaling an alarm if the base needs refilling. One of our readers suggested that he use the tree itself as a low water indicator, which is just what [Eric] did this year. If the water is somewhat low, the Arduino-controlled relay powering the tree is switched off and then on again, every 5 seconds. If the base is nearly dry, the tree asks for water by blinking the word “Water” repeatedly in Morse code.

We think that this year’s solution is pretty clever, and we’re glad to see that [Eric] didn’t give up after last year’s setback!

An Iambic Keyer In 5 Minutes

December 5, 2011 by Brian Benchoff 17 Comments

When most people think about a telegraph key, a piece of 1890s tech with a lever that moves up and down comes to mind. These ‘straight keys’ were terrible for telegraphers and led to repetitive stress injuries like carpel tunnel syndrome..Iambic keys came along and move the contacts to a horizontal position. If you ever see a HAM playing with his CW rig, chances are they’re using an iambic key. It’s great, then, that you can build your own iambic key in five minutes using parts you have lying around.

The build [Dimitris] put up is dead simple – just two metal contacts with a pair of 470K pullup resistors. All this connects to three pins on an Arduino. All the micocontroller needs to do is measure the rise time a touch sensor pin when a voltage is applied. If there’s a finger on the pin, the capacitance increases and the rise time is longer. After that, just assign one sensor as ‘dit’ and the other as ‘dah’ and you’ve got an iambic key.

[Dimitris] put all the code for his project up on his blog. His iambic key seems like the perfect project after a tiny Morse trainer. Check out the video of the key in action after the break

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Trying To Measure The Speed Of Light With An Arduino

December 1, 2011 by Brian Benchoff 63 Comments

We know that measuring the speed of light with an Arduino is possible. It’s just that the implementation is hard.

Last month we saw [Udo]’s blinkenlight shield that can be used as a line scan camera. It’s a neat piece of kit, but [Udo] really wants to submit something for the Buildlounge laser cutter giveaway, so he figured measuring the speed of light would be an easy project. If a kid and a chocolate bar can do it, surely it can’t be too hard.

[Udo] hit upon the idea of pulsing a laser pointer and measuring the time of the reflection. Because his blinkenlight shield can be used as a light sensor, all that’s needed is a mirror and a pretty long line of sight. There’s a few problems with the setup though: with the Arduino running at 16 MHz, a photon will travel 19 meters in one clock cycle.

Even with some very clever coding, we’re not really sure detecting an emitted photon is possible at such (relatively) slow clock speeds. We’re thinking [Udo] could source a few hundred meters of optic fiber so the entire experiment could fit on a desk, but feel free to drop a note in the comments if you’ve got a better idea. [Udo]’s demo of his blinkenlight/laser mashup is after the break.

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Custom Massive LED Panel Lights Up The Party

November 30, 2011 by Mike Nathan 12 Comments

giant-led-sign

The guys at BuildLounge wrote us to share a giant LED sign they came across in the submission pile for their “Win a Laser Cutter” contest that’s currently under way. [Stephen Shaffer] helps run a huge party called Fantastic Planet, for which the group typically outsources the lighting arrangements. They got tired of hiring light guys several times a year and built their own mega display for the festivities instead.

The LED sign consists of 1,474 LEDs that output well over 10,000 lumens. The sign was produced for just about $800, which is very reasonable for a display of its size. The whole thing is controlled by a pair of Arduinos paired with 34 MIC5891 shift registers, all mounted on custom designed PCBs that the group produced in-house.

The display looks great, but don’t take our word for it – check out the video below to see it in action.

If you are interested in taking a closer look at how it was built, swing by the build thread to see more details.

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