A Vintage Single Transistor LED Blinker

[Eric Wasatonic] had a box of SWB2433 transistors that he had very little information about. In order to discover their properties, he fired up his curve tracer to compare these transistors with more common ones. He noticed the SWB2433 exhibited negative resistance while the similar curves of a 2n3904 didn’t. Then he reverse-biased the two transistors: the negative resistance region on the 2n3904 was less than that of the SWB2433, but it was there, and a 2n2222 had a bigger region. Using this knowledge, he developed a relaxation oscillator circuit which uses a negatively biased transistor.

Using one transistor, one resistor and one capacitor, he describes the circuit and how the components affect the frequency of the sawtooth wave the oscillator creates. [Eric] uses the oscillator to build a simple LED blinker and shows what happens when he changes the transistor and adjusts the voltage or resistance. He also shows the circuit as a tone generator and adjusts the tone by replacing the resistor with a potentiometer. And then, for fun, he modifies the circuit to show the oscillator as an AM transmitter. Check out his video after the break.

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The Magnetophone

The Magnetophone

The Magnetophone is the latest electro-acoustic instrument from [Aaron Sherwood]. This tower contains 14 strings, and 14 hand-wound electromagnets. By energizing each electromagnet with a square wave, the strings can be vibrated to create music.

The brains of the device consist of an Arduino Mega attached to the top of the tower. The microcontroller has 6 timers, which allows for 6 notes to play at the same time. An open source tone library was used to generate square waves at the correct frequencies. These square waves are amplified by LM386 based circuits, which provide enough power to the coil to oscillate the string. By using square waves at specific frequencies, overtones of strings can be created.

This isn’t the first time we’ve seen [Aaron] combine strings and electronics. His Glockentar used solenoids to strike strings. However, this project provides new possibilities by allowing the rate of oscillation to be controlled precisely. You can see the instrument in action after the break.

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Zappo the robot mixes tone generator, sensors, alarm clock and more


Now [Kevin] claims he built this robot for his 3-year-old son but we know he just used that as an excuse to spend way too much time in his workshop. The robot is a roundup of all the interesting things you can do with hobby electronics. It’s a great example of what you can teach yourself in one year, as [Kevin] only started tinkering with electronics about fourteen months ago.

The robot centers around an Arduino which manages to control a plethora of auxiliary boards. The alarm clock part of the build has a readout in the center of the robot’s chest. There are a bunch of sounds which can be played as the alarm, including a lot of iconic movie sound bytes. Add to that some playful features — like a tone generator which is altered by the column of potentiometers on the left, motion activated eyes, and sound activated ears — and you’ve got a dream-come-true of a toy for your kid.

As a side note, we wrote this several days ago, but ended up bumping it a couple of times in the publishing schedule. We reached out to [Kevin] to let him know a feature was on the way. When he learned that we bumped it in order to feature [Jamie Matzel’s] giant robot he had to laugh. The two met at a mini Maker Faire about a year ago and that interaction is what gave [Kevin] the confidence to start the project.

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Sinister Tone Generator brings the bass


[RichDecibels] wrote in to share a new device he built called the “Sinster Tone Generator”. It’s basically a bass drone synthesizer that uses two pairs of heterodyning oscillators to generate the output. If you swing by his site, he has a long audio demo of the device in action with a bit of reverb and filtering applied to enhance the sound. After listening, we agree that it sounds pretty sinister!

The device is relatively small and handsomely packaged in a plastic project box he had custom cut by Ponoko. [Rich] says that this particular unit is a one-off that he has produced for a charity auction, and that bidding is open through Sunday if you really want to get your hands on it. If you happen to have the time to build one yourself, he has uploaded schematics and layout files to his site (as usual), so feel free to stop by and grab a copy.