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Last Updated: June 02, 2021 01:45 PM

Circuits Designed by Dave Johnson, P.E. :

Medical_Corona_Monitor  -  The circuit is powered by +5v and has an on-board voltage regulator as a reference voltage.  The current from a reversed biased photodiode is converted into a voltage using an op amp circuit.  That output voltage is fed to a voltage comparator circuit.  Included is an adjustment in the current to voltage converter, to calibrate the installed circuit . . . Dave Johnson, Lubbock TX (Mar 30, 2010)-DC Magazine - Issue 8 Apr 2010

Modified LED Night Light  -  I bought some night lights a few months ago from Walmart here in Denver.  The devices were made by Elumina Lighting Technologies inc. (www.  eluminalighting.  com) , their model LED-6200A.  I think I paid about $15 for a pack of three lights.  I wanted a light . . . Hobby Circuit designed by David A. Johnson P.E.-May 21, 2007

Modified Shake to Charge Flashlight  -  The complete schematic for this device is shown below.  A few things should be pointed out.  First, they use some very cheap 1N4001 diodes in the bridge rectifier circuit instead more efficient Schottky diodes.  They also use a small 0.  5 Farad cap with a . . . Hobby Circuit designed by David A. Johnson P.E.-January 01, 2012

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Mac Mini (Late 2014) ‚ÄĒ The Teardown -  23-Oct-14 -Design News:   It's been two years since the Mac Mini's last appearance on iFixit's teardown table, but a newly revised version joins Apple's lineup this week.  Is this truly a refreshed Mini, or merely a mini-refresh? Stay tuned to find out just what two years of innovation has to say for itself -- it's Mac Mini __ Gadget Freak

Machine Gun -  This circuit produces a sound very similar to a machine gun:__ 555-Timer

Magic Fingers Tickle the Ivories -  1-Apr-10 -Design News:   Imagine, putting on a glove and you can play the piano.  Colorado State University students John Been, Hannah Hudson, Casey O'Farrell and Ryan Slinger created such a glove that detects the bend of a finger and plays a corresponding piano note.  A button on the glove shifts between five high and low __ Gadget Freak-Case #162

Magic Lamp -  No, its not Aladdin's lamp with a genie inside.  This magic lamp appears to be an ordinary frosted light bulb with a rather unusual characteristic.  Whenever your finger is touched across the base threads and center contact the lamp magically lights! Without wires! It is a most effective illusion if you don't make a big production, "Hey! Check out this magic lamp!", but instead casually remove the bulb from a package of new bulbs and pretend to not notice when it lights.  When your victim gasps and grabs the bulb for further investigation just explain away the flash as some sort of static electricity effect and act indifferent. __ Contact: Charles Wenzel of Wenzel Associates, Inc.

Magnetic gun -  When optimally tuned, it will propel a small slug about 1.5 metres high, or 2.5 metres horizontally.  IC1 is a 555 timer in astable mode, sending approx.10 ms pulses to decade counter IC2.  IC2 is continually reset through R3, until pin 15 is taken low through the "Fire" button __ Designed by Rev. Thomas Scarborough

Magnetic Levitation Mystery -  3-Sep-07 -Design News:   Nathan Loden's Magnetic Levitation experiment started with the basic problem of stabilizing a frictionless position control loop with inherent metastability.  A fast controller with phase-lead compensation took care of that.  Then he discovered a strange phenomenon: The levitated object begins and __ Gadget Freak-Case #107

Magnify Your Workbench -  16-Feb-09 -Design News:   William Grill needed a better view of his worktable for prototyping.  He was using a three-times lighted lens mounted on his workbench, but it wasna euro  (TM) t enough for working on small gadgets.  So he created a gadget for gadget prototyping a euro " a monitor that can display his work at 12-times __ Gadget Freak-Case #135

Make a Joule Thief -  In this week's Weekend Projects video podcast, Make Magazine's Bre Pettis and I show you how to make a Joule Thief.  The PDF file that goes with the podcast is here  (450 kB PDF file) .  So whatsa Joule Thief? It's a little wisp of a circuit that __ Designed by Bre Pettis

Make a Potato Battery -  The basic experiment is based on the use of a potato, but many fruits and vegetables work as potential batteries! For the zinc electrode, a large galvanized nail works well.  Nails with a thick, rough zinc texture are preferable to galvanized nails that are smooth __ Designed by © EETech Media, LLC.

Make you own Output Transformer for a Tube Amp -  As anyone who knows about tube amps will tell you, "The output transformer is the most expensive part".  Not is it is only the most expensive part, but is is also probably the hardest part to come by.  Parts for tube amps in general are a lot harder to find then other more common electronic parts.  Transformer theory for power transformers is pretty straight forward and it is fairly easy to find information for winding a power transformer of any type and size.  I have always been intrigued by output transformers and it seemed very hard to get any specific information on how to make one.   __ Designed by Jon Tirone, AKA John Fisher

Maker Movement Celebrates 10 Years of DIY -  19-May-15 -Design News:   Maker Faire celebrated its 10 th anniversary recently with familiar celebrities and top chip companies, its youthful energy and do-it-yourself values intact.  The gathering on the doorstep of Silicon Valley will spread to nearly 200 events attracting as many as a million people this year.  "I believe __ Gadget Freak

Making the Presoak Automatic -  11-May-11 -Design News:   Anyone who presoaks laundry knows the problem.  You fill the washer with clothes, laundry and soapwith the intention of starting the laundry after 20 minutes of soaking.  Two days later you remember it's in there.  Jitendra Tailor decided to solve this problem for once and all with an automated __ Gadget Freak-Case #186

Man's Best Friend -  14-Jan-11 -Design News:   When you want to sleep in during a cold winter morningbut the dog needs to get out of its crateyou can turn to Les Kelly's Easy Out gadget.  Click a controller and the dog's door opens while you get a few more zzz's.  The controller works from many floors away.  Once you push the button, the __ Gadget Freak-Case #178

Mark Liked His Tree Straight Up with a Twist -  10-Jan-05 -Design News:   Mark likes his martinis dry, but never his Christmas trees.  To avoid his tree turning into kindling prematurely, he created an automatic watering device that keeps it fresh and helps it last longer.  His system pumps water from a 1-gal reservoir via a pump powered by a 12V dc power supply.  Level __ Gadget Freak

Mark Took the 4th State of Matter into His Own Hands -  7-Jun-04 -Design News:   Rather than throw his old TV set away, Mark turned it  (along with a few other parts) into a power supply for a plasma globe.  Basic construction of the device is a flyback transformer with primary, feedback, and secondary coils.  Acting like an inductor, the flyback is wired so that the feedback __ Gadget Freak

MarshmalLow Bazooka -  This device uses a PIC12F615 to implement a capacitor discharge ignition system.  When the switch  (button) is closed, the PIC sends pulses to the IRF644 MOSFET creating high voltage pulses to charge the 1.0 uf/250 volt capacitor.   __ Designed by Luhan Monat-Mesa Arizona

Master-Slave Power Switch -  Video:  This gadget is a master/slave power switch which is used to turn a slave device on  (or off, if so wired) when a master device is turned on. The author has built two of these devices to turn speaker systems on and off with his TV or his laptop computer. It could also be used for lamps or other things __ Designed by Andrew R. Morris, Gadget Freak-Case #195, Design News

Matt Resolved to End the Morning Madness -  3-Feb-04 -Design News:   Tired of a wakeup call at the crack of dawn, Matt decided to train his roosters to be less vocal.  So he built a kind of Skinner Box that makes the coop dark when his birds exceed a certain volume.  His crow sensor features a microphone and amplifier that puts out a digitized signal.  A __ Gadget Freak

May the Lightsaber Teardown Be With You -  5-May-15 -Design News:   Redesigning Star Wars' Awful New __ Gadget Freak

Medicine-Time Reminder -  We are all so busy with our daily lives that we forget to take our medicines on time, which can have several ill effects on our health.  The circuit described here...__ Electronics Projects for You

Memory Wire Muscles Actuate Biped -  11-Jul-14 -Design News:   The prototype we are going to build shows one application of memory wire muscles.  They are actuators, like stepper motors or servos, that can be much lighter, have a more organic movement, and are silent.  Though they have some drawbacks  (typically, their torque is not very high, and the typical on/ __ Gadget Freak-Case #258

Microsoft Reveals Motion Sensor Keyboard -  14-May-14 -Design News:   Cabe AtwellIf you've seen any Iron Man film, you've probably fantasized about how cool it would be to have Tony Stark's 3D technology at your fingertips.  While our technological advancements seem eons away, Microsoft Research has potentially created the first of many motion-sensor keyboards to make life just __ Video-Gadget Freak

Midi Key-tar -  18-Sep-14 -Design News:   Have you ever needed an extra synth for a concert? Maybe you just enjoy fiddling around with music production software, and you need a midi controller? Well, look no further than your own computer keyboard.  This simple "weekend project" will leave you with a new, stylish, playable instrument.  This __ Gadget Freak-Case #263

Mini efficient coil launcher from disposable camera flash -  This is a fun and non-dangeros project for those people who like to throw projectiles magnetically.  It simply works by placing a ferromagnetic projectile at one end of a coil and pulsing some power init.  The trick is to switch off power when the projectile is at the middle of the coil, there are some ways to do it but it isn't important now.  The second trick is to use.   __ Contact: IQ Technologies

Mini Mill Battery Charger -  Taking about 30 minutes to make from old computer parts, the Mini Mill will can charge a couple of NiCad batteries.   __ Designed by Flavio Dellepiane

Mini Offline UPS -  Most of the systems are powered by AC mains.  Uninterrupted power supply systems  (UPSes) are there as a back-up to power the systems when mains supply is interrupted due to a...__ Electronics Projects for You

Mini Rechargeable Power Supply -  Presented here is a robust, compact and hand-held power supply that delivers 9.2V and 5V up to 1A  (approx.) and 3.3V up to 500mA.  It also includes a female A-type USB...__ Electronics Projects for You

Mint Tin Bike Light -  This year Iíve been going on a lot of bike rides with friends, sometimes on public roadways, sometimes after dark.  My bike has a nine watt 500 some odd lumen headlight, which makes it easy to see where Iím going, and definitely makes me __ Designed by Radio LocMan

Mobile Electronic Workbench -  Typically, implementing and testing even a small circuit requires an elaborate setup that includes breadboards, a dual DC power supply, hookup wires, ICs and resistors of different values.  This setup can...__ Electronics Projects for You

Mobile Phone Multipower Unit -  Most of the mobile phone complaints are related to the power supply.  This is mainly because of improper charging and use of non-recommended chargers and low-quality batteries.  Depending upon the make...__ Electronics Projects for You

Modified LED Night Light -  I bought some night lights a few months ago from Walmart here in Denver.  The devices were made by Elumina Lighting Technologies Inc.   (www.  eluminalighting.  com) , their model LED-6200A.  I think I paid about $15 for a pack of three lights.  I wanted a light . . . Hobby Circuit designed by David A. Johnson P.E.-May, 2007

Modified Shake to Charge Flashlight -  The complete schematic for this device is shown below.  A few things should be pointed out.  First, they use some very cheap 1N4001 diodes in the bridge rectifier circuit instead more efficient Schottky diodes.  They also use a small 0.5 Farad cap with a . . . Hobby Circuit designed by David A. Johnson P.E.-January, 2012

Moisture Monitor for Plants -  Over-watering and under-watering both are harmful for plants.  Roots need air as well as water.  If the soil is constantly saturated, air cannot reach the roots and they suffocate.  Also, excess...__ Electronics Projects for You

Monster Power Blender is Sweetly Green -  Alternative Energy April 02, 2009__ Gadget Freak-Case 138

Monster Power Blender is SweetlyGreen -  2-Apr-09 -Design News:   Rick Crammond created a turbine blender using the principles of Nikola Tesla.  The Tesla blender achieves accelerated performance by combining water and air pressure simultaneously to the turbine nozzle.  The blender is fueled by an off-grid, self-contained, solar-powered, re-circulating fluid system __ Gadget Freak-Case #138

More Cool Tech from Optimal Design -  25-Feb-15 -Design News:   Joe Wascow, principal at Optimal Design Co., talks about his company's technology during the Pacific Design & Manufacturing Show in Anaheim, Calif. __ Gadget Freak

Motion Controlled Blinking Eyes -  13-May-14 -Design News:   This is Mark II of my Animatronic Eyes, which was created for someone who wanted to animate a rock sculpture.  The eyes themselves were made with plastic Easter egg tops, which fit perfectly as eyelids over ping pong balls.  The problem there becomes one of mounting and alignment.  In this version, __ Gadget Freak-Case #254

Motion Sensor Light Switch -  3-Sep-15 -Design News:   Are there light switches in your home that aren't as conveniently located as you would like? This laser-based switch decoder and driver allows for flexible control of those lights located in less than ideal places.  I live in an apartment.  My kitchen is boring and can be accessed from either end of __ Gadget Freak-Case #272

Motorized Mountainboard -  11-May-09 -Design News:   Here's a skateboard that doesn't need a hill  (or a push-off from your foot) for propulsion.  James Howland and his project buddies, Pat Rimel and Nate Davis, created a motorized mountainboard as a project for their mechanical engineering class at Colorado State University.  The gadget has a handheld __ Gadget Freak-Case #141

Movie Maker -  Like real movies, this circuit makes use of a characteristic of the human eye and brain known as the persistence of vision.  A sequence of still pictures is projected onto a...__ Electronics Projects for You

Moving Beyond Step Counting -  15-Jul-15 -Design News:   Tom EmrichWith a large majority of wearable devices focused on step counting it is no wonder that the accelerometer has become somewhat synonymous with a pedometer.  One of the most common sensors found in tons of gadgets, including wearable tech, the accelerometer is a sensor that, as the name suggests, __ Gadget Freak

Multicolour Curtain Backlights -  This circuit comprises two parts: a string of 5mm high-intensity white LEDs connected in series and the circuit wired around. IC CD4060 with an inbuilt oscillator.  The IC is wired such...__ Electronics Projects for You

Musical Ladybug -  Our son Henk is fond of small animalsbees, bugs, waterbugs, frogs, hedgehogs, newts, fishes and toads.  They are caught in the gardens and ponds around our house and neatly stored in vessels, jars and containers for careful study.  After a few days of confinement they are returned to their natural environment  (and in unhappy cases, caught again within a few days) .  So when we decided to give Henk a radio for his sixth birthday, it could not be a dull grey portable from Radio Shack.  For this special occasion we designed the one and only musical ladybug.   __ Designed by Aren van Waarde

My New Windmill Design Free Power -  A Practical Alternative to help reduce your Heating Bills.   (I wanted to build this as a working unit, but due to health reasons, its not going to happen.)  __ Designed by G.L. Chemelec

Mycestro, a 3D Mouse for the Next Generation -  4-Apr-13 -Design News:   Cabe AtwellNick Mastandrea was flying home from Denver one day two years ago when he noticed a man having trouble working on his computer due to the limited space.  That's when he envisioned the Mycestro, a wireless mouse that mounts to your index finger.  Since that time, he has worked on enhancing his product __ Video-Gadget Freak


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