This Digital IR Theremin creates tones based on the distance of an object from its IR sensor. There’s no microcontroller here, since the project is part of an Introduction to Digital Electronics course. Instead, it uses a handful of comparators, transistors, AND gates, and a 555 timer to make noise.
The comparators are connected to create window comparators. This configuration will output a digital 1 if the input is between two reference voltages, and 0 if it is not. Using this, the analog output of the IR range sensor can be converted to digital values.
The 555 timer takes care of creating the output waveform. A specific resistor is switched in to the timer’s RC circuit depending on which window comparator is active. This allows for a different tone to be played depending on the distance from the IR sensor.
The result is a square wave, which has a frequency dependant on how close an object is to the IR sensor. By selecting the right resistances for each distance, the theremin can be tuned to play a specific scale.
This is a neat project for people looking to learn digital electronics, and the write up does a great job of explaining the theory. After the break, check out a video of the theremin generating some tones.
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The mechanical simplicity of this pull-string controlled most useless machine is delightful. You can see the metal gripper which is reaching up to tug on a light-fixture-style pull chain. This is how it turns itself off after you’ve pulled the string to power it up.
The device is [Alex555’s] entry in the 7400 Logic competition. We do hope that he ends up posting a schematic because we’d love to see the gritty details of how it works. After the break you can watch two doors open, allowing the arm to raise up and the gripper to grab the chain. This takes just four servo motors, which are controlled by the signal from a 555 timer and some accompanying hardware.
Apparently the chain is a fake, as the servos didn’t provide enough force to actuate that type of switch. It’s not a surprise as those pull chains do require quite a tug. An optical sensor was used to trigger the movement when your hand reaches for the chain.
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Get your feet wet with radio frequency transmitters and receivers by working your way through this pair of tutorials. [Chris] built the hardware around a couple of 555 timers so you don’t need to worry about any microcontroller programming. He started by building the transmitter and finished by constructing a receiver.
Apparently the 27 MHz band is okay to work with in most countries as long as your hardware stays below a certain power threshold. The carrier frequency is generated by the transmitter with the help of a 27.145 MHz crystal. The signal is picked up by the receiver which uses a hand-wrapped inductor made using an AL=25 Toroid Core. We’d say these are the parts that will be the hardest to find without putting in an order from a distributor. But the rest of the build just uses a couple 555 timer chips and passive components, all of which will be easy to find. The video after the break shows the project used to receive a Morse-code-style message entered with a push button. It would be fun to interface this with your microcontroller of choice and implement your own one-way error correction scheme.
[Jon Ferwerda] managed to fry the analog electronics on an old electric organ while conducting some circuit bending experiments. It’s a loss, but he’s still left with some cool equipment to play with. Recently he got to work generating tones using the organ’s foot pedals.
There were two types of foot pedal included with this organ, the set that is arranged like a keyboard, and a rocker pedal similar to what you might use with an electric sewing machine. Since the music generation was handled by those fried bits of organ [Jon] got to work interfacing the foot keyboard with a 555 timer. He used a fairly large capacitor to get the frequency into the bass range and wired individual pedals to different parts of a resistor network. But he didn’t stop with that. The rocker pedal has its own variable resistor hardware which lets him bend the pitches are they are being generated which sounds alike like a guitar whammy effect. He shows his work in the clip after the break. We think he nailed it! This is a perfect supplement to any type of electronic music setup.
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Knowing that I’m always happy to get something new and glowy, my wife brought home a cheap “floating pool light” that she found on sale for roughly $10. This is a large white floating ball that has LEDs inside and cycles through different colors. Meant to be put into a pool for neat effects, we found it to be much more interesting just used around the house.
However, it was a bit too bright and cycled colors too quickly for our taste. It was actually somewhat distracting when we were just trying to sit and have a few beers late at night on our patio. This gave me a perfect excuse to tear it apart and start hacking… like I wasn’t going to do that anyway.
What I found inside was extremely simple. There’s a single un-marked chip that holds the different display modes (there were 3 display modes: warm, cool, and white). The LEDs were arranged in an array of Reds, Blues, Greens, and Whites (half marked yellow).
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August 15th 2012, the news was reported that [Hanz Camenzind], the creator of the 555 timer, has passed away. We are all familiar with 555 timer, but many of you may not be aware that [Hanz] also created the first class D amplifier. Actually, he had over 20 patents under his belt as well as a few books.
He is survived by His Wife, Daughter, and three Sons.
If you’re staging some epic Star Wars battles you could go original with Red or Blue lightsabers. But what if you decide you’re more of a fan of Jedi and want to go green? Or perhaps the prequels have inspired you to take on purple? Why choose at build time when you can adjust the color to match your mood.
[Phik] built himself a color-selectable lightsaber using RGB LEDs. He sourced a 5M strip of them from eBay for around $20. The pixels are not individually addressable, but each color channel can be driven with a pulse-width modulation signal to mix and match the final color. Now he could have gone with a microcontroller solution, but [Phik] decided to give himself a bit more of a challenge. He built three PWM circuits based on a 555 timer which can be adjusted with a potentiometer. It’s not going to kill any insects, but the keep-it-simple-stupid aspect of the project makes it something we could actually build ourselves. The same cannot be said for most of the replica builds we see.