The lowly diode, a device with only two leads, can nonetheless do many things. Diodes can detect, rectify, suppress, emit light, detect light, change capacitance, emit microwaves and more. This wide range of use means diodes are included in almost every design and it’s well worth learning more about the inner workings of all kinds of diodes.
My introduction to diodes started like many of my generation with a homemade crystal radio set. My first diode was a piece of pencil graphite in contact with an old fashion safety razor with the joint of the two dissimilar materials — graphite and steel — creating the diode. In this configuration the diode is said to be “detecting” which is the act of turning a weak radio signal into a weak audio signal. At least in my home town of Marion Indiana, one radio station was stronger than the other so that I didn’t have to listen to two stations at once.
I eventually learned about “real” diodes and the 1N34A Germanium diode was my “goto” diode into my teens. Nowadays looking into a modern version of the 1N34A you can still see the semblance of the old “cat’s whisker” by looking carefully into the diode.
A quick and somewhat inaccurate semblance of the way a diode works can be demonstrated with marbles and jacks representing negative electrons and positive “holes”. Holes are basically an atom missing an electron due to the combination of elements, a process known as doping. Join me after the break for the explanation.
Here is a nice project that allows youngsters (but also adults!) to actually see the data stored in a Read Only Memory (ROM). The memory shown in the picture above is made of diodes. [Scott] made it as a part of his Barcamp Fall 2013 presentation about visualizing ROMs. He starts his write-up by stating the obvious: this memory is not practical. Nonetheless, it still was a fun exercise to do. [Scott] then greatly described all the different kinds of read only memories that you can find out there, with a few words explaining how they work. In his diode ROM, bits are ‘programmed’ by adding (or not) a diode between a given data line (anode) and an address line (cathode). When pulling low a given address line, the corresponding data line will only be pulled low if a diode is present. [Scott] finally checked his circuit by using a very old device programmer which could only be run in DOS.
That banner image may seem a little bit theatric, but it’s a good representation of what this 3W handheld laser can really do. Turn the thing on in a slightly smoky room and it looks exactly like a thin beam Lightsaber.
What kind of tricks would you expect this thing to perform? Perhaps it’ll pop some black balloons? Prepare to be shocked because it’s orders of magnitude more powerful than that. The video below shows it burning and igniting a collection of items almost instantly. [Styropyro] tested his creation by igniting paper, cardboard, flash paper, flash powder, burning through a stick of wood, and igniting an undisclosed substance at the end of the video. But one of our favorites is when he drives a solar powered toy car with the intense beam.
He pulled the diode from a DLP projector, and drives it with a pair of 18650 Lithium Ion batteries which are commonly found in laptops. He made the enclosure himself. It looks great but we can’t help but wonder if the components would fit in a painstakingly made replica.
This is the second CNC machine he’s seen through from start to finish. It improves upon the knowledge he acquired when building his CNC mill. The frame is built from pine but also uses bits of plywood and MDF. It can move on the X and Y axes, using drawer sliders as bearings. The pair of blue stepper motors drive the threaded rods which move the platform and the laser mount. Just above the laser he included a small DC fan to keep it from burning up. The control circuitry is made up of an Arduino Nano and a stepper motor driver board. Catch a glimpse of the engraver cutting out some stencil material after the break.
There must be something about Spring that brings out the urge to work with laser diodes. We just saw a similar 1W cutter last week.
It was time for some new T-shirts so [Andreas Hölldorfer] built a laser cutter. Wait, what? That’s the excuse he’s going with, and in the end this scratch built laser cutter did come in handy by cutting stencils to use when decorating his garments.
The first thing we thought when looking at the cutter is where’s the tube? [Andreas] didn’t use a CO2 laser, so this ends up being rather low-powered. The cutting head is a 1W blue laser diode which manages to slice the three-ring binder separator pages he’s using for the stencils. The two-axis machine is mounted inside a wooden box to protect his eyes while it’s cutting. He plans to add a drawer later on so that the cutting bed will slide in and out to swap out material for the next project. He already does a lot of 3D printing work and had an old RepRap driver board on hand to use for this projects. He designed and printed the red mounting brackets which make all of the junk-bin components work together. Not bad!
Obviously this starts by cracking open the dead device and verifying that the culprit is the power supply. [Alan] then removes that board from the chassis and gets down to work with a visual inspection. He’s got several images which illustrate things to look for; blistered electrolytic capacitors, cracked solder joins, scorch marks, etc. In his case there’s obviously a burnt out fuse, but that merely protects the hardware from further damage, it’s not the cause. Next he examines the diodes of the bridge rectifier. These need to be removed from the system to do so, which he accomplishes by clipping one end of each as seen above. He found that two diodes on one side of the bridge had broken down. After replacing them he tries a new fuse which immediately burns out. But a quick swap of the capacitors and he gets the thing back up and running.
The project uses a wheel of luminous paper as the display surface. This has a glow-in-the-dark quality to it which can be charged up using a bright light source. In this case a UV laser diode was used. This is perhaps the best possible source as its intensity will allow for very quick charging. The innovation here is the use of a second disk as a stencil. Look closely in the image above and you will see that the laser diode is mounted perpendicular to the display surface itself. A mirror reflects — and we believe slightly spreads — the laser dot. It then passes through a cut-out on the black wheel which is shaped as the desired character. As you can see in the video after the break, this results in a crisp and clear glowing letter.