History Of The Diode

The history of the diode is a fun one as it’s rife with accidental discoveries, sometimes having to wait decades for a use for what was found. Two examples of that are our first two topics: thermionic emission and semiconductor diodes. So let’s dive in.

Vacuum Tubes/Thermionic Diodes

Our first accidental discovery was of thermionic emission, which many years later lead to the vacuum tube. Thermionic emission is basically heating a metal, or a coated metal, causing the emission of electrons from its surface.


In 1873 Frederick Guthrie had charged his electroscope positively and then brought a piece of white-hot metal near the electroscope’s terminal. The white-hot metal emitted electrons to the terminal, which of course neutralized the electroscope’s positive charge, causing the leafs to come together. A negatively charged electroscope can’t be discharged this way though, since the hot metal emits electrons only, i.e. negative charge. Thus the direction of electron flow was one-way and the earliest diode was born.

Thomas Edison independently discovered this effect in 1880 when trying to work out why the carbon-filaments in his light bulbs were often burning out at their positive-connected ends. In exploring the problem, he created a special evacuated bulb wherein he had a piece of metal connected to the positive end of the circuit and held near the filament. He found that an invisible current flowed from the filament to the metal. For this reason, thermionic emission is sometimes referred to as the Edison effect.

Thermionic diode
Thermionic diode. By Svjo [CC BY-SA 3.0], via Wikimedia Commons
But it took until 1904 for the first practical use of the effect to appear. John Ambrose Fleming had actually consulted for the Edison Electric Light Company from 1881-1891 but was now working for the Marconi Wireless Telegraph Company. In 1901 the company demonstrated the first radio transmission across the Atlantic, the letter “S” in the form or three dots in Morse code. But there was so much difficulty in telling the received signal apart from the background noise, that the result was disputed (and still is). This made Fleming realize that a more sensitive detector than the coherer they’d been using was needed. And so in 1904 he tried an Edison effect bulb. It worked well, rectifying the high frequency oscillations and passing the signals on to a galvanometer. He filed for a patent and the Fleming valve, the two element vacuum tube or thermionic diode, came into being, heralding decades of technological developments in many subsequent types of vacuum tubes.

Vacuum tubes began to be replaced in power supplies in the 1940s by selenium diodes and in the 1960s by semiconductor diodes but are still used today in high power applications. There’s also been a resurgence in their use by audiophiles and recording studios. But that’s only the start of our history.

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Be A Part Of The Best Hardware Conference Ever

The 2016 Hackaday SuperConference is on. If you haven’t had time to submit your proposal for a talk or workshop at the world’s greatest conference for hardware, now is the time to do it. We’re looking for everything – war stories from deep in the trenches or next to the pick and place, the problem of having your board house 5,000 miles from your lab, and that time you accidentally discovered P=NP in the firmware of a reflow toaster oven.

2016SuperconTeaser-cfpThe Hackaday Supercon will be in Pasadena, California on November 5th and 6th, and will be the host of hundreds of hackers, designers, engineers, and the only makers that you want to meet. We’re going to have several venues with talks, workshops, and other various activities.

Talks will be scheduled for 20-40 minutes, and workshops will be scheduled for 1-4 hours. In both cases, topics can range from rapid prototyping, new and interesting techniques, creativity in technical design, and stories of product development and manufacturing.

Last year’s SuperConference was the greatest hardware conference we’ve ever seen. That success was due entirely to the talented engineers, speakers, and presenters of the Hackaday community who put together their stories to share for the benefit of all. If you couldn’t make it, you can still check out all the talks from last year.

If you’re reading this and think you should propose a talk, do it!. Submit your proposal. This conference is only a success because of the awesome Hackaday community and the efforts of readers just like you.

If you’re wondering what the usual talk at the Hackaday Supercon is like, I present (below) the greatest talk I have ever seen. It’s [Jeroen Domburg] a.k.a. [sprite_tm]’s efforts to create a Matrix of Tamagotchis. It’s thirteen Tamagotchis, fully virtualized, emulated, and running on a server, going about their lives without any awareness they’re inside a computer.

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Google Unveils Their Experimental Plan For Wireless Broadband Service

Two years ago, the FCC, with interested parties in Microsoft, Google, and many startups, created the Citizens Band Radio Service (CBRS), a rule that would open up the 3550-3650 MHz band  to anyone, or any company, to create their own wireless backbone between WiFi access points. It is the wireless solution to the last-mile problem, and last year the FCC enthusiastically endorsed the creation of the CBRS.

In a recently released FCC filing, Google has announced their experimental protocol for testing the new CBRS. This isn’t fast Internet to a lamp pole on the corner of the street yet, but it lays the groundwork for how the CBRS will function, and how well it will perform.

Google will be testing the propagation and interference of transmissions in the 3.5 GHz band in places around the US. Most of the Bay Area will be covered in the tests, as well as Boulder, CO, Kansas City, Omaha, Raleigh, NC, Provo, UT, and Reston, VA. Tests will consist of a simple CW tone broadcast in the 3.5 GHz band.

The 3.5 GHz band is already allocated to shipborne navigation and military radar systems, posing an obvious problem to any wireless broadband system using this spectrum. To this end, the FCC is proposing a novel solution to the problem of coexistence between the CBRS and the military. Instead of simply banning transmissions in the spectrum, FCC Chairman Wheeler proposes, “computer systems can act like spectrum traffic cops.” A computer is able to direct the wireless traffic much more effectively than a blanket ban, and will allow better utilization of limited spectrum.

Google’s FCC filing is just for testing propagation and interference, and we have yet to hear anything about how a network built on 3.5 GHz spectrum will be laid out. One thing is for certain, though: you will not have a 3.5 GHz USB networking dongle for the same reason you don’t have a Google Fiber input on your desktop.

Laser Sequencer Uses Arduino To Enable Super-Microscope!

[Philip]’s Laser control Arduino shield.

[Philip Nicovich] has been building laser sequencers over at the University of New South Wales. His platform is used to sequence laser excitation on his fluorescence microscopy systems. In [Philip]’s case, these systems are used for super-resolution microscopy, that is breaking the diffraction limit allowing the imaging of structures of only a few nanometers (1 millionth of a millimeter) in size.

Using an Arduino shield he designed in Eagle, [Philip] was able to build the system for less than half the cost of a commercial platform.

The control system is build around the simple Arduino shield shown to the right, which uses simple 74 series logic to send TTL control signals to the laser diodes used in his rig. The Arduino runs code which allows laser firing sequences to be programmed and executed.

[Philip] also provides scripts which show how the Arduino can be interfaced with the open source micro manager control software.


As well as the schematics [Philip] has provided STEP files and drawings for the enclosure and mounts used in the system and a detailed BOM.

More useful than all this perhaps is the comprehensive write-up he provides. This describes the motivation for decisions such as the use of aluminum over steel due to its ability to transfer heat more effectively, and not to use thermal paste due to out-gassing.

While I can almost hear the cries of “not a hack”, the growing use of open source platforms and tool in academia fills us with joy. Thanks for the write-up [Philip] we look forward to hearing more about your laser systems in the future!