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Gadget Circuits
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Last Updated: October 24, 2017 02:54 PM

Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:

Circuits Designed by Dave Johnson, P.E. :

Tester 4-20ma Current LoopThis circuit injects an adjustable current through a wire loop.  Using a digital current meter, the current can be adjusted from near zero to over 24 milliamps . . . Hobby Circuit designed by David A. Johnson P.E.-May, 2012

Touch Alarm for Door KnobI designed this hobby circuit many years ago and it seems be a very popular construction project.  Many companies offer simple alarm devices for personal use in bedrooms or hotel rooms.  A metal chain attached to a box holding the electronics is place . . . Hobby Circuit designed by David Johnson P.E.-May, 2000

Touch Switch controls a 120 VAC loA - DThis is a capacitance based touch on/touch off switch, which can control power to a 200 watt 120vac load . . . Hobby Circuit designed by David Johnson P.E.-July, 2006

Use Color Film Negative to Make an Optical FilterThis isnít an electronic circuit but the file shows the curve for an optical filter made from exposed color film.  The material blocks most visible light but is very transparent to 880nM infrared light.  Kodak 100ASA is exposed to "cool white" fluorescent light for about 5 seconds . . . Hobby Circuit designed by Dave Johnson P.E.-January, 1998

Vertical Lifting Security Gate Power SourceThe circuit that I came up with is shown below.  It uses 5 identical circuits.  Each one is wired in parallel with it assigned 650F super capacitor.  A LM385 provides a 1.2v voltage reference.  A resistor divider measures the voltage across the capacitor and feeds the voltage to a low power, low voltage op amp.  The output of the op amp drives an n-channel FET.  I designed the circuit for a maximum charge current of 600ma.  This would allow the use of a 10 watt solar panel, if needed, in the future.  Each of the five circuits forms a shunt type voltage regulator, limiting the voltage across each capacitor to about 2.6v.. . . Circuit by David Johnson P.E.-November, 2009

Voltage to Frequency Converter + 1us LED Pulse DriverThis circuit receives the signal from the above amplifier and launches powerful 1uS infrared light pulses from a low cost LED that are frequency modulated by the audio information.  The 10KHz center frequency of the pulse stream is low enough so a standard. . . Circuit by David Johnson P.E.-March, 1999

Wave Power Generator Demo SystE - MAn inexpensive stepper motor is used as a voltage generator in this wave generator demo. . . Circuit by Dave Johnson P.E.-March, 2007

The LP Doctor: Cleaning Up Clicks & Pops -  Part 2: all the construction details.__ SiliconChip

The Musical Pencil -  16-Nov-09 -Design News:   One of the milestones on my path to electrical engineering was sometime around 6th grade, when my parents bought me one of those 150-in-1 electronics kits, the one with all the wires and spring terminals, and point to point directions for wiring things up.  I didnít understand a lot of what the __ Gadget Freak

The New GoPro Hero4 Session Gets a Teardown Session -  23-Jul-15 -Design News:   The GoPro Hero4 Session is the company's smallest camera model yet, and also the first waterproof GoPro.  Let's find out what's going on inside of it. __ Gadget Freak

The Nick-Off Bad Cat Deterrent -  Do you have a miscreant "puddy-tat" that likes to jump on kitchen benches  (or worse) ? It can be a real problem, especially at night when no-one is looking.  The Nick-Off Cat Deterrent  (aka the Ted-Off) is the perfect solution.  It uses an infrared sensor to detect said cat and triggers an answering machine to play back simulated, demented barking.  It also lights two white LEDs which form the eyes of an angry dog.__ SiliconChip

The Tube to the Recycling Center Has an Air Ride -  24-Sep-07 -Design News:   Let's say you have a Beer Chucking Refrigerator within range and a Can Crusher out in the shed.  Now all you need is a way to get the empties out to the can crusher without having to get up and walk out to the shed.  Here it isyou just pop the empty can into this vacuum transporter and thwap! __ Gadget Freak-Case #108

The Ultimate Wireless Volume Control -  17-Aug-11 -Design News:   Andrew Morris decided the usual wireless volume controls donít offer enough functionality, so he created the ultimate volume control that connects between a computer or MP3 player and an amplified speaker system. __ Andrew R. Morris, Gadget Freak-Case #192

The Ultra-Portable 'MoGo' Laptop Mouse -  I've wanted an ultra-portable laptop for a long time because lugging a heavy full-sized laptop around on trips was just no fun.  After much research, I had narrowed down the choices to a Toshiba Satellite U200-PT7 or a Lenovo 3000 V100.  They were almost identical __ Designed by Stefan Vorketter

The Window Watcher -  24-Oct-14 -Design News:   The Window Watcher stops the burglar before he does damage or enters the house.  House alarm service companies set off alarms and call the service only after the burglar has damaged and entered the house.  Window Watcher employs an infrared passive thermal detector with a very narrow beam.  The simple __ Gadget Freak-Case #266

There's Still Time to Vote for  of the Year -  3-Dec-13 -Design News:   The final showdown is under way in our first-ever  of the Year contest.  Who will win an all-expenses-paid trip to the Pacific Design & Manufacturing Show? It's up to you, dear readers, to tell us. __ Gadget Freak

This App Detects Cancer -  3-Jul-14 -Design News:   Cabe AtwellAdvancements in technology never cease to amaze us, but the DermoScreen is a show stopper.  The app can scan moles and lesions to detect whether they are likely to become malignant.  Its developers at the University of Houston say it has an 85% accuracy rate.  The iOS app, still in testing, is not __ Gadget Freak

This Student's Batsuit Will Protect You in a Real Fight -  2-Mar-15 -Design News:   Chris WiltzIf you want to get your hands on a Batsuit it only takes a trip to the costume shop.  But good luck trying to fight crime in one not that vigilantism is that good of an idea anyway.  Fans and cosplayers are always making their own Batsuits, but Jackson Gordon  (no known relation to Commissioner __ Gadget Freak

This Watch Lets You Feel the Time -  21-May-14 -Design News:   Cabe AtwellIf you or someone you know is vision impaired, you know how difficult it can be to do something as simple as check the time.  Eone Timepieces recently developed a universal timepiece to address this issue that will likely change the way watches are designed for the blind.  The new timepiece is called __ Gadget Freak

Thunder Cloud Lamp Brings the Storm Indoors -  11-Mar-15 -Design News:   Elizabeth MontalbanoThere's nothing more exciting or terrifying -- depending on your perspective -- than a summer thunderstorm.  Well now you can have one right inside your house thanks to a multi-sensory experience courtesy of Cloud, a gadget that is part lamp, part sound experience.  Designed by Richard Clarkson of __ Gadget Freak

Tic Tac CubedDueling in 3D -  8-Feb-11 -Design News:   Matthew Katzenstein has created a 3-D Tic Tac Toe game.  It lights up with an interactive knob and is programmed to play two- and three-player versions.  The game is a color-coded 3x3 RGB LED matrix.  Tic Tac Cubed is controlled by an Arduino Diecimila, a microcontroller board based on the ATmega168 __ Gadget Freak-Case #180

Timer for Mosquito Destroyer -  In electric-heating mosquito repellents, an electric vaporiser heats up a mat or liquid to release non-degrading chemicals into the air and keep the mosquitoes away from the closed surroundings.  Here's a circuit...__ Electronics Projects for You

TinkerBots Gives Tots a Robotic Building Kit -  14-May-14 -Design News:   Elizabeth MontalbanoTwo German engineers has created a toy set that let kids build robots from individual modules much in the same way they snap Legos together.  The TinkerBots set of kinetic modules and passive pieces is like Legos on steroids.  In fact, Kinematics, the company that offers the building kit, says Lego __ Gadget Freak

Todd's Fascination with Flight -  2-Jun-03 -Design News:   Now he always knows how high he is in the sky, thanks to a portable altimeter he designed using a micromachined pressure transducer.  By exploiting the inverse relationship between air pressure and altitude and compensating for nonlinearities, the device produces acceptable accuracy  (plus or minus __ Gadget Freak

Toilet Paper Roll for the Challenged -  2-May-07 -Design News:   Now here's a gadget that could actually catch on and do some good for folks unable to do the basic tasks many of us take for granted.  It's a "Toilet Paper Dispenser Deluxe Makeover!" This patent-pending gadget preloads, folds and cuts metered lengths of toilet paper with a wave of the hand on the __ Gadget Freak

Touch Alarm for Door Knob -  I designed this hobby circuit many years ago and it seems be a very popular construction project.  Many companies offer simple alarm devices for personal use in bedrooms or hotel rooms.  A metal chain attached to a box holding the electronics is place . . . Hobby Circuit designed by David Johnson P.E.-May, 2000

Touch Switch controls a 120 VAC loA - D -  This is a capacitance based touch on/touch off switch, which can control power to a 200 watt 120vac load . . . Hobby Circuit designed by David Johnson P.E.-July, 2006

Touch-Sensitive Audio Desk Trays -  23-May-14 -Design News:   This Christmas, I received a MaKey MaKey , which turns everyday conductive objects into keyboard buttons.  Seeing as it runs on top of Arduino, I wanted to explore the same touch-sensitive capabilities on my Arduino Uno.  These trays, unlike normal trays with printed labels, have audio labels. __ Gadget Freak-Case #255

Toy Car Hack -  This car measures just 5 1/2 inches in length.  It was sold as a remote control car for $19.95 at Fry's Electronics here in Phoenix.  Powered by 4 AAA batteries, it has a small dc motor and a very interesting steering mechanism.   (08/08/08)  __ Designed by Luhan Monat-Mesa Arizona

Toy MachineGun Zaps Pests -  5-Oct-10 -Design News:   Do neighborhood animals dig up your flower beds or get into your trash? Rick Prescott created a computer-controlled "machine gun" to help deter local pests, including the two-footed kind that invade work cubes.  Rick mated an infrared sensor with a Nerf-brand gun that shoots spongy "bullets" to __ Gadget Freak-Case File #173

Toy Organ -  Some useful circuits using the LM555 IC.  Scroll to find the toy organ circuit __ Designed by Jose Pino

Transistor_matching -  A fixture and a method of matching the VBE of transistors __ Designed by Dick Cappels

Turn off the Heater behind Me -  26-Apr-11 -Design News:   Ed Nauman had a bad habit of leaving his workshop at night without turning off the heater.  His wife would get up in the morning and findto her consternationthe workshop was plenty toasty.  In the interest of keeping peace in his household, Ed decided to create a gadget that would save the __ Gadget Freak-Case #185

Turning a Flash Camera into a Coin Toss -  10-Dec-07 -Design News:   Joe Groele of Allegany, N.Y., took a flash camera, added a few electronic components and turned it into a coin-tossing gadget.  He converted the flash into a strobe, then he ran the electricity through a coil to create a magnetic field.  "The changing magnetic field causes an electric current in the __ Gadget Freak-Case #113

TV remote control jammer -  Scroll to this oneDo you have an incessant channel hopper that is driving you crazy? Or perhaps you simply want to enforce your own selections.  The TV Remote Control Jammer will do the trick.  This circuit is a redo of an older design which is not effective on modern remotes.  Modern remote controls are hard to jam but with a little care this circuit will do the job.  The circuit is just a flasher operating at 40 kHz which is the carrier frequency used by common remote controls.  The strong 40 kHz infrared flashing interferes with the signal from the remote. 
 __ Contact: Charles Wenzel of Wenzel Associates, Inc.

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