Avalanche pulse generator design

avalanche-pulse-generator

This avalanche pulse generator is a great way to test your mettle as an Electronics Engineer. The challenge is to truly understand how each part of the design works. We certainly got a failing grade when first studying the schematics more than a week ago. But we’re slowly beginning to understand what’s going on under the hood.

The concept of an avalanche transistor is some wicked voodoo from the analog side of the street which leverages a transistor’s breakdown voltage to achieve a predictable result. In laymen’s terms it (mis)uses a transistor to produce a really fast pulse. The write-up linked above references several previous avalanche pulse generator designs, but this one is a bit different in how it produces about 50V from a pair of AAA batteries using a multivibrator circuit.

Even if you have no idea what’s going on here you may be interested in the last few paragraphs where the circuit is measured using a cutting-edge Teledyne LeCroy Wavemaster 820Zi-A. That’s a 20 GHz scope with a 15.3″ screen which you’ll never ever own.

Building a ’60s guerilla homebrew square wave generator

What do you do when you’ve got three broken function generators? Build your own, obviously. Since your workshop has already gone through three of these bad boys, you might find yourself repairing your build. Better not use any fancy ICs and go with a transistor only build.

When [Miroslav] sent in his ‘guerilla homebrew’ square wave generator, we were really impressed. With a relatively simple schematic that uses parts that could be salvaged from old radios, this is a real MacGyver build.

The generator is based around a simple astable multivibrator. It doesn’t provide sine waves, but it’s the easiest circuit to get working. The build started off with a quartet of 2N4401 transistors, but according to the datasheet and the venerable Tektronix 502A, these had a very bad rise time compared to 2N3904s.

[Miroslav]‘s project generates square waves up to 2.22 MHz and pulses with a variable duty cycle from 1-49% and 51-99%. Output is either 5 Volt TTL levels or an adjustable 0-3.38 level. The generator is exactly what [Miroslav] needed, so that makes it a great tool in our book.

Faking high-speed video photography of repetitive events

[Destin] has been doing some high-speed and high-resolution video photography using a standard DSLR. He accomplishes this using a bit of ingenuity to capture images of repetitive events at slightly different points in time.

The banner image above shows a bullet travelling through a set of matchsticks. [Destin] uses the sound of the gun firing to trigger the flash that captures the image. A piezeo transducer picks up the sound, triggering a precision pulse generator. That pulse generator then triggers the flash, adding a delay based on the settings. In this way, [Destin] can capture video by firing a bullet for each frame, but adjusting the delay period of the pulse generator to capture the image when the bullet is in a slightly different place from the previous frame. It’s an old technique, but after some post-processing it produces a high-quality output without sinking thousands of dollars into an actual high-speed camera. Check out the video we’ve embedded after the break.

We like this guy’s style. We saw him strapping a camera onto a chicken back in December and we hope to see a lot more from him in the future.

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