WTF is Degaussing?

The modern office has become a sea of LCD monitors. It’s hard to believe that only a few years ago we were sitting behind Cathode Ray Tubes (CRTs). People have already forgotten the heat, the dust, and the lovely high frequency squeal from their flyback transformers.

Image by Søren Peo Pedersen via wikipedia
Image by Søren Peo Pedersen via wikipedia

There was one feature of those old monitors which seems to be poorly understood. The lowly degauss button. On some monitors it was a physical button. On others, it was a magnet icon on the On Screen Display (OSD). Pressing it rewarded the user with around 5 seconds of a wavy display accompanied by a loud hum.

But what exactly did this button do? It seems that many never knew the purpose of that silly little button, beyond the light-and-sound show. The truth is that degaussing is rather important. Not only to CRTs, but in many other electronic and industrial applications.


Of Shadow Masks and Aperture Grilles

Close up of a shadow mask by Rauenstein via Wikipedia
Close up of a shadow mask by Rauenstein via Wikipedia

A CRT has quite a few components. There are three electron guns as well as steering and convergence coils at the rear (yoke) of the tube. The front of the tube has a phosphor-coated glass plate which forms the screen. Just behind that glass is a metal grid called the shadow mask. If you had enough money for a Sony screen, the shadow mask was replaced by the famous Trinitron aperture grille, a fine mesh of wires which performed a similar function. The shadow mask or aperture grille’s  job is to ensure that the right beams of electrons hit the red, green, or blue phosphor coatings on the front of the screen.

This all required a very precise alignment. Any stray magnetic fields imprinted on the mask would cause the electron beams to bend as they flew through the tube. Too strong a magnetic field, and your TV or monitor would start showing rainbows like something out of a 1960’s acid trip movie. Even the Earth’s own magnetic field could become imprinted on the shadow mask. Simply turning a TV from North to East could cause problems. The official term for it was “Color Purity”.

magnet-trickThese issues were well known from the early days of color TV sets. To combat this, manufacturers added a degaussing coil to their sets. A coil of wire wrapped around the front of the tube, just behind the bezel of the set. When the set was powered on, the coil would be fed with mains voltage. This is the well-known ‘fwoomp and buzz’ those old TV sets and monitors would make when you first turned them on. The 50 Hz or 60 Hz AC would create a strong moving magnetic field. This field would effectively erase the imprinted magnetic fields on the shadow mask or aperture grille.

Running high current through the thin degaussing coil would quickly lead to a fire. Sets avoided this by using a Positive Temperature Coefficient (PTC) thermistor in-line with the coil. The current itself (or a small heating coil) would heat up the PTC, causing resistance to increase, and current through the coil to drop. After about 5 seconds, the coil was completely shut down, and the screen was (hopefully) degaussed.

As time went on monitors became embedded systems. The PTC devices were replaced by transistors controlled by the monitor’s main microcontroller. Monitor manufacturers knew that their sets were higher resolution than the average TV set, and thus even more sensitive to magnetic fields. Users are also more likely to move a monitor while using it. This lead the manufacturers to add a degauss button to the front of their sets. A push of the button would energize the coil for a few seconds under software control. Some monitors would also limit the number of times a user could push the button, ensuring the coil didn’t get too hot.

Holding a magnet near the front of a black and white (or a monochrome ‘green screen’) CRT created visible distortion, but no lasting damage. Mid-century hackers who tried the same trick with their first color TV quickly learned that the rainbow effect stayed long after the magnet was moved away. In extreme cases like these, the internal degaussing coil wouldn’t be strong enough to clear the shadow mask.

Commercial degaussing coil
Commercial degaussing coil

When all else failed, a handheld degaussing coil or wand could be used. Literally waving the magic wand in front of the screen would usually clear things up. It was of course possible to permanently damage the shadow mask. Back in 2007, I was working for a radar company which had been slow to switch to LCD monitors. Being a radar shop, we had a few strong magnetron magnets lying around. One of these magnets was passed around among the engineers. Leaving the magnet under your monitor overnight would guarantee rainbows in the morning, and a shiny new LCD within a few days.

Queen Mary, showing her degaussing coil

CRTs aren’t the only devices which use degaussing coils. The term was originally coined in 1945 by Charles F. Goodeve of the Royal Canadian Naval Volunteer Reserve (RCNVR). German mines were capable of detecting the magnetic fields in a naval ship’s steel hull. Coils were used to mask this field. The Queen Mary is one of the more famous ships fitted with a degaussing coil to avoid the deadly mines.

Even mechanical wristwatches can benefit from a bit of degaussing. A watch which has been magnetized will typically run fast. Typically this is due to the steel balance spring becoming a weak magnet. The coils of the spring stick together as the balance wheel winds and unwinds each second. A degaussing coil (or in this case, more properly a demagnetizer) can quickly eliminate the problem.

A story on degaussing wouldn’t be complete without mentioning magnetic media. Handheld or tabletop degaussing coils can be used to bulk erase floppy disks, magnetic tape, even hard disks. One has to wonder if the degaussing coils in monitors were responsible for floppy disks becoming corrupted back in the old days.

So there you have it. The magic degaussing button demystified!

Hacklet 108 – Simple Functional 3D Prints

We featured 3D printer projects on last week’s Hacklet. This week, we’re looking at a few awesome projects created with those printers. Trying to pick great 3D printed projects on is a bit like staring at the sun. There are just way too many to choose from. To make things a bit easier, I’ve broken things down into categories. There are artistic prints, complex mechanical or electronic prints, and then there are simple functional prints, which is the topic we’re featuring today. Simple functional prints are designs which perform some function in the world. By simple, I mean they have only a few moving parts or electronic components. Let’s get right to it!

cornersWe start with [Scott] and L Extrusion Endcaps. Every Home Depot, Lowes, or hardware store has a selection of extruded aluminum. Typically there are a few flat bars, and some L brackets. L brackets are great, but they can be a pain to work with. Most of us don’t have the skills or the tools to weld aluminum, so nuts and bolts are the only way to go. [Scott’s] given us another option. He’s designed a set of 3D printable brackets that slip onto the ends of the brackets. The brackets make quick work of building boxes, racks, or anything with 90° or 45° angles.


earbudNext up is [Joe M] with 3D Printed Molds: Custom Silicone Earbuds. [Joe] had a set of Bluetooth earbuds he enjoyed, but the rubber tips left a bit to be desired. Not a problem when you have a 3D printer on hand. [Joe] measured the plastic part of his earbuds and the rubber tips from a different set he liked. A bit of CAD magic later, and he had a model for the perfect earbud tip. While he could have directly printed the tip in a flexible filament like NinjaFlex, [Joe] opted for a pure silicone tip. He printed molds, then mixed silicone caulk with cornstarch (as a catalyst). The resulting earbuds sound and feel great!

coil2Next we have [Jetty] with Highly Configurable 3D Printed Helmholtz Coil. Helmholtz coils are used to create uniform magnetic fields. Why would you want to do that? It could be anything from measuring magnets to cancelling out the effect of the earth’s magnetic field on a device being tested. [Jetty’s] wrote an OpenScad program which allows the user to enter parameters for their coil. [Jetty’s] program then calculates the coil’s magnetic properties, and outputs a printable .stl file. Building the coil is as simple as printing it and wrapping some copper wire. [Jetty] found that his coil was within 60nT (nanoTesla) of the expected value. Not bad for a bit of plastic and wire!


scope1Finally we have StickScope,  [SUF’s] entry in the 2016 Hackaday Prize. Like many of us, [SUF] loves his StickVise. Sometimes you need a bit of magnification to see those tiny 0201 resistors though. [SUF] had a cheap USB microscope on hand, so he designed StickScope, a USB microscope mount designed especially for the StickVise. Two 6mm steel rods are the backbone of the design. 3D printed clamps hold the system together like a miniature boom microscope. This is actually the third revision of the design. [SUF] found that the original design couldn’t be used with parts close to the bar which holds the microscope. A small jaw extender was the perfect tweak.


If you want to see more simple functional 3D printed projects, check out our new simple functional 3D prints list! If I missed your project, don’t be shy, just drop me a message on That’s it for this week’s Hacklet. As always, see you next week. Same hack time, same hack channel, bringing you the best of!

DIY Vein Finder Shows you Where to Stick It

Everyone who’s donated blood, gotten an intravenous (IV) line put in, or has taken a blood test knows that little bit of anxiety before the needle goes in. Will this be a one stick operation, or will the phlebotomist do their impression of drilling for oil while trying to find a vein? Some of us are blessed with easy to find blood vessels. Others end up walking out looking like they’ve been in a fight with a needle.

[Alex’s] wife girlfriend is a nurse who’s had trouble finding veins in the past. [Alex] is an automotive engineer by trade, more acquainted with oil lines than veins and arteries. While he couldn’t help her himself, [Alex] designed this 3D printed vein finder to help his wife girlfriend out at work. He started by studying devices on the market. Products like Veinlite use LEDs to illuminate the skin. Essentially these products are a string of LEDs and a battery. They are patented, FDA approved, and will set you back between $188 and $549 USD. [Alex] and his wife girlfriend couldn’t afford that kind of cost, so he built his own. Continue reading “DIY Vein Finder Shows you Where to Stick It”

Hacklet 107 – 3D Printing Projects

3D printers have forever changed the hardware hacker movement. From the original RepRap project on up through current commercial offerings, 3D printers have become an indispensable tool for hackers, makers, and engineers. While printers may not have started a desktop manufacturing revolution, they are a desktop prototyping evolution. It’s rare for a day to go by on Hackaday without a project that uses a 3D printed part in some way shape or form. These printers also continue to evolve, with new projects pushing the technology ever forward. This week’s Hacklet is all about some of the best 3D printer projects on!

reprapWe start with [TTN] and Icepick Delta. [TTN’s] passion is creating 3D printers as cheaply as possible. The Icepick definitely succeeds at this. Icepick’s frame is made of wood. The motors are commodity steppers. Control is via the long proven Ramps 1.4 board, which can be picked up with drivers and an Arduino Mega clone for under $35 these days. A few ball bearings and metal parts fill out the vitamins of this design. Just about everything else is 3D printed in true RepRap style. The printer is currently running Marlin firmware, but [TTN] plans to move to Repetier in the future.

Even with these humble origins, Icepick manages to print at a very respectable 50 mm/s before frame flex becomes a problem.  Prints at 0.1mm layer height look great, on par with any current commercial printer.

strataNext up is  [Machinist] with 3D printer brain retrofit. Commercial 3D printers have been available for decades now. This means some of the older models are getting a bit long in the tooth. [Machinist] has a very tired 15 year old Stratasys Dimension 768. The mechanics of the Dimension are still in good shape, but the electronics have seen better days. [Machinist] is ditching all the old electronic hardware (and the DRM which goes with it) and setting this machine up with a Smoothieboard 5X. So far the Dimension has been gutted, and [Machinist] has gotten the monster stepper motors playing sweet music with his new control board. I can’t wait to see how this project progresses.

coffeeNext we have [jcchurch’s] Coffee Maker Delta 3D Printer. [jcchurch] has managed to convert an old Norelco coffee maker into a mini sized 3D printer. The warmer plate has even become a heated bed for ABS prints. Unlike Icepick up top, the aim of this design is to use as few 3D printed parts as possible. The idea is that this would be the first printer to build when you don’t have another printer handy. Think of it as a caffeinated RepStrap. According to [jcchurch], this printer has been running strong at Tropical Labs for over a year. You can even pull the delta assembly off and make a pot of coffee! The coffee maker printer is still somewhat of a teaser project. If you see [jcchurch] online, tell him to head over and give us more details!

linearFinally, we have [DeepSOIC] with linear stepper motor 3d printer. 3D printers all use good old fashioned rotary stepper motors. [DeepSOIC] is trying to eliminate all that rotary motion, along with the belts and pulleys required to convert to linear motion. Linear stepper motors can be thought of as regular stepper motors, just unrolled. They tend to be very expensive though, so [DeepSOIC] is building DIY versions. His first attempt was to print motor parts using BlackMagic3D’s ferromagnetic filament. This lead to a whole separate project to measure the permeability of the filament. Unfortunately, the filament isn’t permeable enough to act as a motor for a printer. [DeepSOIC] hasn’t given up though. This is the type of project we love – one that might not work out, but really gets people thinking. Check out the comment thread on the project to see collaboration at work!

If you want to see more 3D printer projects, check out our updated 3D printer list! If I didn’t wake up early enough to catch your project, don’t be shy, just drop me a message on That’s it for this week’s Hacklet. As always, see you next week. Same hack time, same hack channel, bringing you the best of!

Hacklet 106 – Robots That Teach

One of the best ways to teach electronics and programming is with hands-on learning. Get the concepts off the computer screen and out into the real world. Students of all ages have been learning with robots for decades. Many older Hackaday readers will remember the turtle robots. These little ‘bots would drive around drawing shapes created in the logo programming language. This week’s Hacklet is all about the next generation of robots that teach electronics, mechanics, programming, and of course, hacking. So let’s check out some of the best educational robot projects on!

edubotWe start with [Tom Van den Bon] and Edubot Controller (Benny). Buying one or two robots can get expensive. Equipping a classroom full of them can break the bank. [Tom] is hoping to make robots cheaper and more accessible with Edubot, his entry in the 2016 Hackaday prize. Edubot rides on a 3D printed frame with low-cost gear motors for a drive system. Edubot’s brain is an STM32F042, a low-cost ARM processor from ST micro. The micro and motor drives are integrated into a custom board [Tom] designed. He’s has even begun creating lesson plans so students of various ages and skill levels can participate and learn.

microbotNext up is [Joshua Elsdon] with Micro Robots for Education. Big robots can be intimidating. They can also cause some damage when hardware and software created by budding engineers doesn’t operate as expected. Tiny robots though, are much easier to wrangle. [Joshua ] may have taken tiny to an extreme with these robots. Each robot is under 2 cm square. The goal is for each one to cost less than  £10 to produce. These micro bots have big brains with their ATmega328P micro controllers. [Joshua] is currently trying to figure out a low-cost way to produce wheels for these robots.

Next we have [shamylmansoor] with 3D printed mobile robot for STEM education. Robots are expensive, and international shipping can make them even more expensive. [Shamyl] is shooting for a robot which can be made locally in Pakistan. 3D printing is the answer. The robot’s chassis can be printed on any FDM printer. Wheels,and tires are low-cost units. Motors are RC servos modified for continuous rotation. The brains of the robot is an Arduino Mega 2560, which should provide plenty of inputs for sensors. [Shamyl] even included a solderless breadboard so students can prototype circuits and sensors right on the robot’s body.


plobotFinally we have [Rodolfo] with Plobot. Plobot is a robot designed for the youngest hackers – those from four to seven years old. [Rodolfo] designed Plobot to be programmed with RFID cards. Each card contains a command such as move forward, turn, start, and reset. Many of the language mechanics are inspired by the Scratch programming language. Plobot’s processor is a Sanguino, running [Rodolfo’s] custom code. An ESP8266 allows Plobot to be connected to the outside world via WiFi. [Rodolfo] has even created a custom over the air update system for Plobot’s firmware. Plobot has already been tested with students, where it made a great showing. We’re hoping both [Rodolfo] and Plobot do well in the 2016 Hackaday Prize!

If you want more mind hacking goodness, check out our brand new educational robot list! Did I miss your project? Don’t be shy, just drop me a message on That’s it for this week’s Hacklet, As always, see you next week. Same hack time, same hack channel, bringing you the best of!

Carbon Monoxide: Hunting a Silent Killer

Walt and Molly Weber had just finished several long weeks of work. He was an FBI agent on an important case. She had a management job at Houghton Mifflin. On a sunny Friday evening in February of 1995, the two embarked on a much needed weekend skiing getaway. They drove five hours to the Sierra Mountains in California’s Mammoth Lakes ski area. This was a last-minute trip, so most of the nicer hotels were booked. The tired couple checked in at a lower cost motel at around 11:30pm on Friday night. They quickly settled in and went to bed, planning for an early start with a 7am wakeup call Saturday morning.

When the front desk called on Saturday, no one answered the phone. The desk manager figured they had gotten an early start and were already on the slopes. Sunday was the same. It wasn’t until a maid went to check on the room that the couple were found to be still in bed, unresponsive.

Continue reading “Carbon Monoxide: Hunting a Silent Killer”

Hacklet 105 – More Mind and Brain Hacks

A mind is a terrible thing to waste – but an awesome thing to hack. We last visited brain hacks back in July of 2015. Things happen fast on Miss a couple of days, and you’ll miss a bunch of great new projects, including some awesome new biotech hacks. This week, we’re checking out some of the best new mind and brain hacks on

We start with [Daniel Felipe Valencia V] and Brainmotic. Brainmotic is [Daniel’s] entry in the 2016 Hackaday Prize. Smart homes and the Internet of Things are huge buzzwords these days. [Daniel’s] project aims to meld this technology with electroencephalogram (EEG). Your mind will be able to control your home. This would be great for anyone, but it’s especially important for the handicapped. Brainmotic’s interface is using the open hardware OpenBCI as the brain interface. [Daniel’s] software and hardware will create a bridge between this interface and the user’s home.


biofeed1Next we have [Angeliki Beyko] with Serial / Wireless Brainwave Biofeedback. EEG used to be very expensive to implement. Things have gotten cheap enough that we now have brain controlled toys on the market. [Angeliki] is hacking these toys into useful biofeedback tools. These tools can be used to visualize, and even control the user’s state of mind. [Angeliki’s] weapon of choice is the MindFlex series of toys. With the help of a PunchThrouch LightBlue Bean she was able to get the EEG headsets talking on Bluetooth. A bit of fancy software on the PC side allows the brainwave signals relieved by the MindFlex to be interpreted as simple graphs. [Angeliki] even went on to create a Mind-Controlled Robotic Xylophone based on this project.

brainhelmetNext is [Stuart Longland] who hopes to protect brains with Improved Helmets. Traumatic Brain Injury (TBI) is in the spotlight of medical technology these days. As bad as it may be, TBI is just one of several types of head and neck injuries one may sustain when in a bicycle or motorcycle accident. Technology exists to reduce injury, and is included with some new helmets. Many of these technologies, such as MIPS, are patented. [Stuart] is working to create a more accurate model of the head within the helmet, and the brain within the skull. From this data he intends to create a license free protection system which can be used with new helmets as well as retrofitted to existing hardware.

mindwaveFinally we have [Tom Meehan], whose entry in the 2016 Hackaday Prize is Train Your Brain with Neurofeedback. [Tom] is hoping to improve quality of life for people suffering from Epilepsy, Autism, ADHD, and other conditions with the use of neurofeedback. Like [Angeliki ] up above, [Tom] is hacking hardware from NeuroSky. In this case it’s the MindWave headset. [Tom’s] current goal is to pull data from the TAGM1 board inside the MindWave. Once he obtains EEG data, a Java application running on the PC side will allow him to display users EEG information. This is a brand new project with updates coming quickly – so it’s definitely one to watch!

If you want more mind hacking goodness, check out our freshly updated brain hacking project list! Did I miss your project? Don’t be shy, just drop me a message on That’s it for this week’s Hacklet, As always, see you next week. Same hack time, same hack channel, bringing you the best of!