Demonstrating The Photoelectric Effect Using Neon Lamps

August 28, 2024 by Dave Rowntree 30 Comments

Neon lamps are fun to play with. These old-school indicators were once heavily utilized in many types of equipment for indication purposes but now seem largely relegated to mains voltage indication duties. Here’s a fun video by [Ashish Derhgawen], discussing the photoelectric effect of neon lamps with some simple demonstrations.

[Ashish] demonstrates the well-known photoelectric effect by triggering a sub-biased neon lamp with visible light from an LED. Neon bulbs work on the principle of voltage-induced ionization, creating a visible glowing plasma. If the applied voltage is high enough, around 60 to 80 V, electrons get knocked off the neutral neon atoms. The now free electrons, roaming around highly energized, will eventually come across a neon ion (missing an electron) and recombine to make it neutral again.

The results are a lower total energy state, and the difference in energy is resolved by the emission of a photon of light, which, in the case of neon, is a dull reddish-orange. Nothing unusual there. However, nothing will happen if the applied voltage bias is just below this device-specific threshold. There’s not enough energy to strip electrons.

Apply an external light source, and this threshold can be exceeded. The photons from the LED are just energetic enough to strip a small number of electrons from the surface of the electrodes, and this causes a cascade, or avalanche effect, lighting up the plasma and turning on the neon lamp. ~~Take away the external light source, and it dies down and goes dark.~~

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CMOS Oscillator Circuit Gets An Eatable Input

September 24, 2022 by Lee Wilkins 9 Comments

In interaction designer [Leonardo Amico]’s work Processing Decay, lettuce is used as an input to produce sound as an element within a CMOS circuit.

We’ve all seen lemons and potatoes doubling in science-fairs as edible batteries, but lettuce is something else. [Leandro]’s circuit uses alligator clips to insert lettuce into oscillators in this audio generating circuit — we think they’re behaving like resistors. Without refrigeration, the resistance of the lettuce changes, and so does the oscillation in the circuit. In a matter of hours, days, and weeks the cells degrades slowly, modulating the system and its sonic output. What a way to make music!

This hack isn’t the freshest — the video dates from nine years ago — but this is the first lettuce circuit we’ve seen. Of course, we love other food hacks like these multi-wavelength lasers used to cook 3D-printed chicken, or maybe the circuit can make use of this neural net detecting fruit ripeness.

32C3: 20 Oscillators In 20 Minutes

January 3, 2016 by Elliot Williams 25 Comments

In terms of implausible stand-up comedy, [Darsha]’s “20 Oscillators in 20 Minutes” is pretty far out there. First of all, she’s sitting down, with googly eyes on her multimeter, and five breadboards and a mess of 9V batteries laid out in front of her. “Has anybody built electronics before? Has anybody built electronics in front of this many people before? Yeah, so you’d better f**king be nice.” And she’s off!

“Square waves are really good for your speakers.” And a few seconds later, a lub-dub beat-frequency oscillator filled the hall. And then there’s the stand-up clichés: “Anyone in the audience from Norway?!” And “Anyone know what chip I’m using here?” (The 555.) A heckler, or participant, shouts up “What are you doing?” She responds “Building this!” and shows a sketch of the basic layout.

She baits the audience — “Do you want to ask me about duty cycles?” — and tells stories: “And then one time the solder fell in my lap and burned through my crappy jeggings. Who knows what jeggings are? Whooo!!” All the while the clicking gets louder and more complicated.

Then there’s the suspense. “11 minutes left? Shit, I dunno if I’m going to make it this time!” She’s visibly panicked. A question: “How do you protect the outputs from overvoltage?” “I don’t. (pause, laughter) I use some filter caps and just, well, hope that you guys have good insurance.”

Nearing the home stretch, there’s this quasi-rhythmic ticking and pulsing slowly building up in the background. She plugs in another capacitor, and the crowd spontaneously applauds. A little bit later, she shouts “Is it loud enough?” over the din and turns it down. At the end, the timing’s getting really tight, and she calls up someone to help from the audience.

We won’t spoil it, naturally. You’ll just have to watch it run to the end. We laughed, we cried. It was better than Schroedinger’s cats.

(We’d use hex inverters.)

ThingamaKIT: Make Your Own Thingamagoop

July 3, 2008 by Juan Aguilar 4 Comments

Bleep Labs’ Thingamagoop is a small synthesizer packed with wacky controls for generating unique sounds; you can now build an expanded version yourself with the ThingamaKit. Made “because there are not nearly enough beeping, zapping, bixxerfouping, anthropomorphic synthesizer monsters in the world,” it generates sounds of different pitches depending on the type and intensity of light hitting a photocell on the front panel. It’s most unique feature, is its LEDacle, which is something like a tentacle with an LED on the end. This can be pointed towards the photocell to modulate the sound. Output is through a 1/4″ audio jack.

Bleep Labs sells fully assembled Thingamagoops for $100, but the new DIY kit is available for half price. The kit version of the Thingamagoop has more controls, two photosensors, and two LEDacles. You can buy it with or without the case, and it doesn’t require any complex wiring. Look after the break for video of some Thingamagoops in action.

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