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Last Updated: June 02, 2021 01:45 PM

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

Circuits Designed by Dave Johnson, P.E. :
AC Current Controls Hour Meter  -  Many systems require routine maintenance based on machine operation time.  The circuit below is a simple way to turn on a hour meter whenever AC power is supplied to the machine.  An inexpensive snap-on current transformer from Magnetics inc, is used to . . . Circuit by David Johnson P.E.-February 13, 2010

Automotive Electrical Voltage Indicator  -  This circuit will indicate if an automotive electrical circuit has zero volts or 12 volts present.   . . . Circuit by David A. Johnson P.E.-July 09, 2006

A Barometer That Measures Your Height -  31-Jul-09 -Design News:   Here's a weather instrument the Dodecahedral Barometer that can actually determine how tall you are by reading the barometric pressure between your head and your feet.  Mark Thoren notes that his gadget was inspired by the release of some new electronic products.  The first is a Serta model 270 __ Gadget Freak-Case #145

A Cat or Dog Detector for Pet Door -  This circuit uses one tuned coil for on the door and just a single wire loop on the animals collar.  When the two coils come close together, it produces a signal that can cause a an LED to light and also trips a solenoid to unlock the door so it can open.  Since all these doors are somewhat different, I leave __ Designed by G.L. Chemelec

A Fish Caller -  Click and click may not sound like much, but to a fish is it a dinner bell __ Designed by G.L. Chemelec

A French Revolutionary Clock -  December 16, 2015   If you run a search online, you will discover so-called metric or decimal clocks for sale.  But be careful -- these clocks have what looks like a metric face  (10 hour markings and numbering) , but use a standard 12-hour mechanism, with 60 seconds per hour and 60 seconds per minute.  Such a clock is not a metric clock at all. __ Gadget Freak-Case #275

A Fridge That's Alert for Midnight Snacks -  22-Oct-07 -Design News:   When you've popped in your fridge alarm, getting peckish in the middle of the night and forgetting to close the dooralong with escalating electricity billswill be a thing of the past.  Italian inventor Flavio Dellepiane has designed a 3V battery-powered fridge alarm that beeps if you leave the __ Gadget Freak-Case #110

A Futuristic Twist on Model Trains -  24-May-11 -Design News:   For those who love model trains, here's a peek at the futurea solar-augmented monorail.  Joe Kopacz and his brother Justin created the monorail from scratch.  Joe, a mechanical engineer at Colorado State University, created the gadget for a school contest.  The monorail includes break regeneration __ Gadget Freak-Case #187

A Good Cheap way to make PCB's (Printed Boards) from Photo Paper -  Every once in a while you come across a very simple idea that helps change your way of doing things or saves you a lot of time and money.  This just so happened to be one of those ideas for me.  I love ideas that can be had using locally available materials as not to depend so much on specialized sources giving me a slight feeling of freedom and immortality.  Ha! __ Designed by Jon Tirone, AKA John Fisher

A Hot-Wire Cutter with Inbuilt Heat Controller -  If you've ever tried to cut polystyrene    (especially!) and polyurethane materials using a saw, razor blade or knife, you'll know that the results are invariably less than satisfactory.  If you are after a clean, precise cut, a hot-wire cutter is the answer.  The hot wire actually melts the material and results in a very neat, very fine cut, without the thousands of bits of foam flakes you normally get.__ SiliconChip

A Matrix Multi-Tool for the HP 35s Programmable Calculator -  Programmable Calculator Software

A Momentary High Voltage Arc -  Can be used to Ignite a barbeque or a Gas in a Potato Gun.   __ Designed by G.L. Chemelec

A Motorized Time-Lapse Camera Slider -  28-Mar-17 -Design News:   Automation & Motion Control,Consumer Electronics, Automation __ Gadget Freak

A Powerful Stun Gun 3 -  Presented Here For Informational Purposes only, Not for Actual Construction! __ Designed by G.L. Chemelec

A Quick-and-Dirty DC Motor Controller -  31-Oct-16 -Design News:   Years ago my pal Steve Titus wanted to experiment with some drone rotor designs.  He needed a simple motor controller that could operate from 8V to 12V and deliver amperes of current to a DC motor used in radio-controlled aircraft  (figure 1) .  I whipped out a design based on the classic TL494 PWM  ( __ Gadget Freak

A Quick'n'Easy Digital Slide Scanner -  A simple way to copy slides onto your computer's hard drive.  Do you have a large collection of slides which are deteriorating by the day? Are they growing mouldy or becoming discoloured? Then there is no time to waste.  Get them onto your computer's hard drive before it is too late.  This method is very quick, simple and does not require any electronics.__ SiliconChip

A SCA Adapter -  For Advertisement Free Background Music on FM.   __ Designed by G.L. Chemelec

A Spiffy Face-Lift for an Old-Time Toy -  January 05, 2009Luis Fernando Espinal Ceballos of Colombia wanted to give his cousin's son the slot track racing set he loved as a child.  But the toy seemed unbearably old-fashioned.  So Luis jazzed it up with a new electronic control system.  He dumped the old battery box and replaced it with a used PC power supply and rewired the entire system for tighter control.  He also added a lap counter to the circuit and upgraded the cars from old Lotus models to new Porsche and BMW models. __ Gadget Freak-Case #132

A Stroke of Genius for Smart TVs -  4-Nov-15 -Design News:   In this age of the Internet of Things  (IoT) , connected devices are getting smarter.  We have smart phones, smart homes, smart cars, smart appliances, and even smart TVs.  But this last example begs the question:  If my TV is so smart, why is my remote control so dumb? Anyone who has tried to use a __ Gadget Freak

A tater tossing page with electronic igntion -  Does it really matter what you build your shooter out of? I've heard that PVC is more brittle than ABS.  I've heard that when PVC would shatter into thousands of small pieces, ABS would just tear.  I have, however, been nearly missed by a large piece of ABS that was "torn" from a potato gun.  So I don't think it really matters, it all depends if you'd rather be hit with many small pieces of PVC or one large chunk of ABS.  I kind of like ABS 'cause it's black __ Designed by Greg Miller

AC Current Controls Hour Meter -  Many systems require routine maintenance based on machine operation time.  The circuit below is a simple way to turn on a hour meter whenever AC power is supplied to the machine.  An inexpensive snap-on current transformer from Magnetics Inc, is used to. . . Circuit by David Johnson P.E.-February, 2010

Accent Lights Are a Crowning Achievement -  23-Nov-09 -Design News:   As a way to set the mood in his family room, when he remodeled Joe Peck put multi-color LEDs behind the crown molding.  The major circuit uses a microcontroller and LED drivers located in a closet, and a small circuit board at each room corner to connect to red-green-blue LEDs.  Perhaps Joe's lights __  Gadget Freak-Case #153

Accurate Electronic Stopwatch -  Here is a simple circuit which can be used as an accurate stop-watch to count up to 100 seconds with a resolution of 0.01 second or up to 1000 seconds with...__ Electronics Projects for You

AIR Ioniser -  This air ioniser is built around an NE555 timer IC which is configured in astable mode.   __ Designed by Rohan B. Rebello

AirDog Drone Provides the Ultimate Selfie -  11-Jul-14 -Design News:   Cabe AtwellIn the young adult novel Extras , everyone in the city of Yokohama is followed by their own personal floating cameras.  Their goal is to produce the top viewed video on the city's local Internet of sorts.  Yes, it's to be the most popular! Although the protagonist seeks to be the least popular, I __ Gadget Freak

Alarm Sounds When Refrigerator Door Remains Open Too Long -  Not properly closing a refrigerator door will no doubt invite huge electricity bills.  This gadget is an alert device that beeps if you leave the refrigerator door open for more than 20 seconds.  When the door opens, the lamp illuminates __ Designed by T.A. Babu

Alarm tells you to close the refrigerator door -  25-Jun-09 EDN-Design Ideas A simple gadget that you place inside the refrigerator alerts you by beeping if the door stays open for 20 seconds or longer Design by Boris Khaykin, TRW Automotive, Livonia, MI

All Aboard the Matzo Bus -  28-Mar-07 -Design News:   While I usually try to steer clear of any bus-related news, I just couldn't pass up the chance to get your feedback on this most unusual invention! When police responded to an early-morning report of smoke in a New York neighborhood, I doubt they expected to uncover this tasty gadget a school bus __ Gadget Freak

Alternative Boards -  Maybe I'm not the only one who does this, but I have found that I can quickly and easily create PCB's by simply soldering the components to the copper area of the circuit board without making holes in it.  This makes custom circuit boards fast and easy and the layout much less critical.   __ Designed by Jon Tirone, AKA John Fisher

Altoids Tin LowFER Transmitter -  Here's a complete LF Beacon transmitter for LowFER    (Low-Frequency Experimental Radio) .  The transmitter is designed for license-free operation between 160 kHz and 190 kHz, consuming the legal limit of 1 watt power input to the final RF output stage.  For fun, the complete transmitter is built into an Altoids mint tin.  The circuit is built dead-bug style on a piece of copper clad circuit borad material, lightly painted with Testors transparent Hot Rod Red to prevent tarnish.  The paint doesn't seem to make soldering any more difficult.  The board is grounded to the tin in a few places.   __ Contact: Charles Wenzel of Wenzel Associates, Inc.

Ambulance Siren -  This siren circuit simulates police, fire or other emergency sirens that produce an up and down wail.   __ Contact: Charles Wenzel of Wenzel Associates, Inc.

Analog Clock Measures Time in Meters -  18-Jun-10 -Design News:   Alan Parekh took a different approach to time keeping with his electronic clock that registers hours, minutes and seconds on individual multimeters.  A microcontroller keeps track of time and calculates the current each meter needs to move its needle at the proper rate.  A separate MCU output drives __ Gadget Freak-Case #166

Animal-Centric Wire Winders & Clips -  21-May-07 -Design News:   Now here are a few fun twists on keeping your desk under control.  The company cableorganizer.com offers some fun and appealing cord control solutions.  These animal-centric wire winders and clips are a quick and easy way to add personality to your workspace.  And if you’re allergic to animals, but __ Gadget Freak

Animated Weather LED Display -  21-Mar-14 -Design News:   This project displays the weather in the form of an animation on an LED matrix  (32x32 resolution or 1024 LEDs) .  The Raspberry Pi is periodically pulling weather conditions from the Internet and then sending a corresponding animated gif weather animation to the IOIO board and LED display.  IOIO is an __ Gadget Freak-Case #252

Another Game Show Timer -  Several Game Show timers included, scroll to find this one.  Here is a somewhat more complex version that uses easily found bipolar transistors.  Note that it requires only two wires between stations and base and those wires can be connected anywhere on the "buss".     (You can wire each station back to the base unit or "daisy chain" the stations from one to the next with only one set of wires going back to the base unit.)  __ Contact: Charles Wenzel of Wenzel Associates, Inc.

Apple Creates MoreGadgets -  26-Mar-07 -Design News:   It began with the Apple computer, followed with the iMac , the iPod , docking stations for your iPod and coming this summerthe iPhone .  And now Apple has something else to offer us allthe Apple TV box.  No, it won't be shaped like an Apple  (though honestly who knows at this point) .  It's a __ Gadget Freak

Arduino Solar Charge Controller -  8-Aug-14 -Design News:   Solar power has the advantages of being low-maintenance and pollution-free, but the main drawbacks are high fabrication costs and low energy conversion efficiency.  Since solar panels still have relatively low conversion efficiency, the overall system costs can be reduced using an efficient solar __ Gadget Freak-Case #260

Arduino-Controlled Namaste Greeting Robot -  The concept of controlling various servo motors through Arduino Uno board is introduced here with a fun project called ‘namaste robot.’ The robot turns its head by 180° and scans people...__ Electronics Projects for You

Aristo Multilog Nr.970 Simulator -  This simulator is based on the impressive collection of Pickett slide rule simulators by Derek Ross.  Derek has given me permission to use his JavaScript code, which I have enhanced to add the digital readouts of the scales that you see above.  The movable parts of the slide rule are implemented using the Drag & Drop for Images and Layers library

Array of blinking neon lamps -  Here is a line powered array of blinking neons designed for continuous duty.  It would be quite dangerous to power a circuit directly from the power line so some form of isolation is needed.  Since most experimenters will not have 120 volt isolation transformers __ Contact: Charles Wenzel of Wenzel Associates, Inc.

ArroW & Line Running LED's -  Our ARROWERL10 has many applications; fill your party with running blinking ARROWERS.  Mount the ARROWER on your bicycle so you'll be more visible and have a safer ride when signaling.  Mount it on a sign as an direction indication.  Place ARROWER anywhere you’d like to draw attention and a smile.  The unique small design will allow you to mount it almost anywhere.   __ Contact: Kit from Elich Industrial Development, Corp

Attention-Grabbing 'Blue Light Special' -  16-Mar-09 -Design News:   William Grill wanted to draw attention to a trade show booth.  He considered a big neon sign, loud music and a provocative attitude, but instead he created this attention-getting gadgethis "Blue Light Special." Grill made this gadget with a mere $15 in materials.  It is built around Microchip __ Gadget Freak-Case #137

Audible timer that can be used as a cooking timer for roasting peanuts for example -  I like to roast my own fresh peanuts , I require exactly 15 mins in the oven at 350oF, the same goes for my muffins for 20 mins and a few other short periods.  It has to be just right but I’ll be darned if I can set up that oven timer properly.  I was getting fed-up with overdone peanuts so I found this dandy little circuit and added to it and changed a few things stuffed it in a little box and take it with me to watch TV while my peanuts are in the oven.   __ Designed by © Laurier Gendron, Burnaby, B.C., Canada

Automated Doggy Door Cares for Your Best Friend -  17-Mar-08 -Design News:   The Automated Doggy Door feeds your dog, replenishes his water and lets him out into the backyard.  Markus Lutz and his team of students at Colorado State University created this complex system that reads your dog's collar and opens the doggy door.  The door can also be opened by a step switch right __ Gadget Freak-Case #117

Automated Plants Watering SystE - M -  During summers, most people are too lazy to water the potted plants on their rooftop gardens every day.  Explained in this section is a simple and exciting plant watering system that...__ Electronics Projects for You

Automatic Curtain Closer -  This circuit uses a mixture of transistors, an IC and a relay and is used to automatically open and close a pair of curtains.  Using switch S3 also allows manual control, allowing curtains to be left only partially open or closed.  The circuit controls a motor that is attached to a simple pulley mechanism, to move the curtains__ 555-Timer

Automatic Device Locator -  Circuit + Notes Tony van Roon  VA3AVR

Automation Comes to the Harmonica -  11-Mar-11 -Design News:   Advanced Automation has been edging into our working lives for decades.  While most of the inroads made by automation have been in manufacturing, these technologies are being increasingly applied in entertainment.  Jon Sorkin has created a gadget that plays programmed songs with a harmonica. __ Gadget Freak-Case #182

Automobile Hidden Door Unlock Button -  27-Sept-04-Design News:  This modification to an automobile is the addition of a hidden unlock button to the automobile. The button is usually recessed in a hole in the underside of the drivers side mirror. The purpose of the button is to prevent the driver from accidentally leaving his keys in the car and not being able to retrieve them __ Gadget Freak-Case #79

Automotive Electrical Voltage Indicator -  This circuit will indicate if an automotive electrical circuit has zero volts or 12 volts present.. . . Circuit by David A. Johnson P.E.-July, 2006

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