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Last Updated: June 02, 2021 01:45 PM

Circuits Designed by Dave Johnson, P.E. :
Telescope_Coin_Operated  -  My client owns several coin operated telescopes.  Their problem is that the battery needs to be replaced every few months.  I needed to design a new circuit to control the shutter.  The solenoid used was too power-hungry.   . . . Dave Johnson, Lubbock TX (Jan 30, 2010)-DC Magazine - Issue 6 Feb 2010

Tester 4-20ma Current Loop  -  This 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.-November 02, 2004

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 29, 2000

Touch Switch controls a 120 VAC load  -  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 11, 2006

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

Table Saw Quick Cleanup -  14-Dec-09 -Design News:   When John Dawson turns on his table saw he wants a Shop-Vac (R) to automatically turn on, too.  He might have controlled a duplex outlet from a wall switch, but where's the fun in that? Instead, he uses a Hall-Effect sensor to detect current flow in the saw's power cord and then turn on the vacuum __ Gadget Freak-Case #154

Tactile Pressure Sensors Can Enhance Google Glass -  18-Oct-13 -Design News:   Jae SonThe high-tech world is waiting with bated breath to see whether Google Glass breaks the mold as a truly life-changing innovation, or shatters expectations as little more than a novelty.  Capable of live sharing, taking pictures of, and translating the wearer's field of vision, the wearable, head- __ Gadget Freak


Take a Teardown 'Voyage' With Kindle -  18-Nov-14 -Design News:   Look and be amazed! Amazon has added a new tablet to its e-reader lineup, and this one aims to perfect the reading experience.  But can it beat Amazon's rocky repairability record? Join us on an incredible journey to the center of the Voyage, and find out just what's inside.  Click on the Amazon __ Gadget Freak

Talk to Your Mirror, Find the Sun, and Have a Swim at Night -  7-Jul-16 -Design News:   Rob SpiegelAs we move through the from the past, we getting into much more complex gadgets that mostly solve actual problems.  This collection includes everything from a digital timer for night swimming to an automated doggie doors that frees the pooch remotely.  Click the image to begin the __ Gadget Freak

Talking Fish Hack -  These items were sold nationally several years ago.  The fish would sing, open its mouth, turn its head, and flap its tail.  After removing the back panel, all of the existing electronics were removed leaving only the 3 servo motors, speaker and photocell)  __ Designed by Luhan Monat, Mesa, AZ

Talking Frog Box -  This device 'listens' to a conversations and then interjects words and phrases at inappropriate times.   __ Designed by Luhan Monat-Mesa Arizona

Talking Morse Code Practice Computer -  Schematic Only __ Designed by Ken Staton

Talking to Your Gadgets Remotely -  September 22, 2008  Design News:  created a gadget that allows you to use your cell phone to control appliances and alarms from a distance__ Gadget Freak-Case #126

Teen Develops Flashlight Powered by Human Hand -  18-Jul-13 -Design News:   Elizabeth MontalbanoWhile other teenagers are out with their friends or playing video games, 15-year-old Ann Makosinski of Victoria, British Columbia, is inventing energy-harvesting devices that she hopes will make the world a better place.  Her latest invention -- the Hollow Flashlight , which runs solely on heat __ Gadget Freak

Teen Invents iPhone-Charging Insole -  14-Jul-14 -Design News:   Elizabeth MontalbanoThe Google Science Fair is proving to be a showcase for talented young inventors.  In last year's contest we saw then 15-year-old Ann Makosinski's flashlight powered by the human hand , and then 17-year-old Eric Chen's novel method for developing a new type of anti-flu medicine among the prize- __ Video-Gadget Freak

Telephone Voice Changer -  Although this kind of voice effect can be obtained by means of some audio computer programs, a few correspondents required a stand-alone device, featuring microphone input and line or loudspeaker outputs.  This design fulfills these requirements by means of a variable gain microphone preamplifier built around IC1A, a variable steep Wien-bridge pass-band filter centered at about 1KHz provided by IC1B and an audio amplifier chip  (IC2) driving the loudspeaker.  

TempBug -- Internet-Connected Thermometer -  26-Jun-14 -Design News:   Last January, we had some trouble with the heat in my office -- specifically, the kind of trouble wherein the heat is not on, you turn it up, and it is still not on.  This went on for more than a few days and finally ended a day or two after we got an email announcing that the heat was broken and __ Gadget Freak-Case #257

Temperature Controlled Ovens -  Here is a simple temperature controller suitable for a variety of purposes; it was designed to heat the copper float out of a toilet for a barometer! __ Contact: Charles Wenzel of Wenzel Associates, Inc.

Ten-Channel Light Controller -  A 10 channel light controller using PWM/ up to 1a per channel at 12v __ Contact: P. Townshend EduTek Ltd

Tesla Turbine Creates Liquid Electricity -  1-Jun-09 -Design News:   If your electricity fails in a post-apocalyptic world, you can use water pressure to generate electricity.  Travis Lipstein and fellow students in a mechatronics class at Colorado State University used a Tesla turbinebased on the work of Nikola Tesla in the early 1900sto turn water into __ Gadget Freak-Case 143

Tesla Turbine Puts Points on Pesky Pencils -  13-Nov-09 -Design News:   Rick Crammond has found a way to improve the Tesla turbine design and give it an update that can sharpen pencils at 2,200 rpm.  That's some fast cranking.  The turbine alone can reach speeds of 8,000-to-12,000 rpm before it self-destructs.  So, Rick built a "bullet-proof" containment box.  The turbine __ Gadget Freak-Case #152

Tesla-Inspired iPhoneDesign News-Gadget Freak  Case Pulls Energy from Air to Charge Device -  15-May-15 -Design News:   Elizabeth MontalbanoA startup inspired by Nikola Tesla -- in name and in engineering -- is about to launch an energy-harvesting smartphone case that can charge your phone on the go.  Nikola Labs has developed a smartphone case that, like the original Tesla battery, works with radio waves.  In the case of the technology __ Gadget Freak

Tester 4-20ma Current Loop -  This 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

Testing Parts 'til They're Toast -  7-Jan-08 -Design News:   Mark Thoren and Jim Williams needed to test the temperature compensation scheme of a circuit they were designing.  The lab had several temperature chambers, but they were always in use.  In frustration, Jim grabbed a brand new toaster and plopped it down on Mark's desk, saying, "This will do." Not __ Gadget Freak-Case #114

The "Sooper Snooper" -  Listen in on conversations, bird calls, noisy engine bearings or even the sound of termites munching into your home.__ SiliconChip

The $250 3D Printer & Custom Cookie Cutter -  27-Jun-14 -Design News:   Cabe AtwellAs we all know, 3D printing is revolutionizing the way we manufacture products today.  Not everyone is excited about the technology, however.  While some cloud-based programs and printers support the free transmission of designs and blueprints, others are taking advantage of this plethora of free __ Gadget Freak

The 13 Most Ghoulish HalloweenGadgets -  26-Oct-16 -Design News:   Clearly, zombies are in this year -- taking over from a decade of vampire dominance in Halloween fashion. __ Gadget Freak

The Attack Dyno -  5-Aug-15 -Design News:   The Attack Dyno brings car enthusiasts an attack timer and dynamometer in a small, portable package with the ability to output vehicle torque, speed, horsepower, 1/4 mile times, 0-60 mph acceleration times, ambient air temperature, and more. __ Gadget Freak-Case #270

The Autonomous Blimp -  Automation & Motion Control April 27, 2009__ Gadget Freak-Case 139

The Autonomous Blimp -  27-Apr-09 -Design News:   Here's a blimp with its own ideas of flight.  Nick Wagner and his fellow classmates at Colorado State University designed their infraLED Zeppelin to maneuver in two modes.  The first is remote control mode where a transmitter sends directional commands  (forward, back, left and right) to the blimp and __ Gadget Freak-Case 139

The Autonomous Zombie Defense SystE - M -  18-Aug-16 -Design News:   Michael Frenzer  The Zombie Defense System automatically learns the shape of a given area  (distances to objects at various angles) . It will then actively scan the area using an ultrasonic sensor and fire a laser at any approaching zombies. The system is run off of a Arduino Uno R3 and can also be connected to a PC via USB for data readouts. __ Gadget Freak

The Best Podcasts Every Engineer Should Be Listening To -  26-Feb-15 -Design News:   Chris WiltzWith National Engineers Week in full swing it's the perfect time to discover something new.  And if you don't have a favorite podcast yet it's about time you fired up iTunes and found one.  But aside from standup comedy and serialized murder mysteries there's a lot out there on the science and __ Gadget Freak

The Case of the Failing Bus Transmissions -  29-Sep-11 -Design News:   Rob SpiegelBack in the 90s when I had just graduated with my mechanical engineering degree, I took a position with a small, privately-owned company building electric buses and shuttles.  The company's shuttles were used in many locations such as Santa Barbara, Santa Monica, Burbank, and more.  They made some __ Gadget Freak

The Curious Incident of the Dog in the Night -  26-Sep-05 -Design News:   Sometimes you can't teach an old dog new tricks.  Tired of trudging down the stairs to let his dog out of his cage in the middle of the night, Les designed a remote control door opener.  The system consists of a clevis mounted to the shaft of a solenoid and the door latch of the cage.  When Les __ Gadget Freak

The Curious Incident of the Dog in the Night (UPDATED) -  30-Jan-07 -Design News:   Sometimes you can't teach an old dog new tricks.  Tired of trudging down the stairs to let his dog out of his cage in the middle of the night, Les designed a remote control door opener.  The system consists of a clevis mounted to the shaft of a solenoid and the door latch of the cage.  When Les __ Gadget Freak

The Dripper! (Modified-works better!) -  Scroll down to find circuits.  Just when you get all comfy in bed you hear itDripDripDrip.  But when you stumble into the bathroom to give the faucet a twist, the dripping sound stops.  After a few trips back and forth you venture out without turning on the lights- to "sneak up" on the drip.  The only problem  __ Contact: Charles Wenzel of Wenzel Associates, Inc.

The FaceMelter3000 -  26-Jul-11 -Design News:   Joe Groele wanted to create some unique electric guitar sounds. __ Gadget Freak-Case #191

The Greatest IoT Nodes of All Ourselves -  29-May-15 -Design News:   Tom EmrichFrom our fridges to our thermostats to our cars, the physical world is slowly becoming connected through the Internet of Things.  Building a network of connected things promises to make our lives easier and more efficient by allowing our smart things to do most of the work for us.  But if we are __ Gadget Freak

The Handy Rival -  3-Jun-15 -Design News:   The Handy Rival is an arcade game that allows an individual to play rock, paper, scissors against a robotic hand.  When the user puts on the glove, movement is detected and the displays turn on  (see figure 1) .  Blinking LED lights prompt the user to select either the "Best of Three Rounds" or the " __ Gadget Freak-Case #268

The Incredible Lego 'Great Ball Contraption' -  5-Nov-12 -Design News:   Sylvie BarakHey -- check out the largest, most intricate Lego machine we've ever seen! __ Video-Gadget Freak

The Inexpensive Dimmable LED Desk Lamp -  30-Nov-12 -Design News:   Andrew Morris designed a dimmable LED driver circuit that is simple and energy efficient.  He then installed the circuit into a portable fluorescent lamp. __ Designed by Andrew Morris-Gadget Freak-Case #230 11/30/2012

The Leaky Tree -  26-Jun-15 -Design News:   The Leaky Tree is a high-quality device designed to dispense ice and one of four mixed drinks that can be selected by the user.  This device was created to quickly mix complex drinks with great precision as well as entertain the user in the process.  The Leaky Tree will conveniently pour an __ Gadget Freak-Case #269


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