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Last Updated: December 01, 2017 04:49 AM


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Circuits Designed by Dave Johnson, P.E. :

Cheap Close-Up Camera Lens  - I often use my digital camera to take photos of some electronic projects.  At times, I need to get in close to capture some details.  But, without some additional optics, my camera just could not maintain focus, as I received closer to an object.  Being a cheap . . . Hobby Circuit designed by David A. Johnson P.E.-April, 2005

Chicken Coop Door Opener with Timer  -  I received an email from a guy in Australia who was trying to build a chicken coop system.  He was planning on using a conventional garage door mechanism to open and close the 6 doors to the coop.  The commercial door opener opened and closed the doors with a single pushbutton.  He wanted to install a standard 220vac powered timer so he could open the doors in the morning and close them at night. . . Circuit by David Johnson P.E.-March, 2013

Click Sound Generator  -  Often in computer controlled systems, you would like to generate a “click” sound whenever a button is pressed.  This provides the user with audible feedback that the pushbutton press has been acknowledged.  The two circuits below generate such a sound.  A click sound is generated each time the logic input swings from a logic low to high condition. . . Circuit by David Johnson P.E.-January, 2009

Coin Operated Telescope  -  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.. . . Circuit by David A. Johnson P.E.-January, 2010

Color Film Makes Optical Filter - This isn’t 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. . . Circuit by David A. Johnson P.E.-January, 1998

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. . . Circuit by David A. Johnson P.E.-February, 2010

CT 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 . . . Hobby Circuit designed by David A. Johnson P.E.-February, 2010

Candy Bowl Counter  -   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.  This software knows when an attending takes a piece of candy from the bowl, and even keeps track of calories. __ Gadget Freak

Car Imobiliser  -   a switch operated by keypad and pin.  Can be used as a car imobiliser or simple combination switch __ Contact: P. Townshend EduTek Ltd

Cardboard AM Radio Resonant Loop Passive Booster Antenna  -   An excellent use for copper wire, a trimmer capacitor and some lovely cardboard.   __ Designed by Henry 

Carl Specialized in Java Apps  -   8-Nov-04 -Design News:   Carl has taken "breakfast in bed" to the ultimate with his remote-controlled coffee pot activation system.  By disassembling his coffee maker, an alarm clock, and remote control car  (and a tad bit of rewiring) , he was able to employ the alarm signal as the on/off power supply to the car's handheld __ Gadget Freak

Cat & Dog Repeller  -   Nowadays, just about every house has an outside lamp with a motion sensor.  Such a device eliminates the need to feel your way to the front door, and it apparently also scares away intruders.  The only problem is that free-running dogs and cats in the neighborhood have little regard for such lamps and continue to deposit their excrement in the garden, once they have found a habitual location there for this purpose.__ I. Fietz © Elektor Electronics Magazine

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

Cat Toy with a Small Weighted Motor  -   The PIC12F675 is small in size and low in power.  It lends itself to some really off-beat uses __ Designed by Luhan MonatMesa Arizona

Centrifugal fish autofeeder  -   This easy as well as cheap but effective device is mainly intended for your ease to leave your fish autofed.  You need no longer worry your fish would starve as this autofeeder would replace your job.  This autofeeder device will expell pellets by quantity as well as time intervals as you like.  Besides, making this circuit seems to be a bit entertaining as you are insisted to make it yourself and so It would develop your creativity.  Don�t worry, it works! __ Designed by Lukman Wijaya lukmannet @ yahoo.com

Changing Electric Field Detector  -   Yes, you read correctly, it's a ghost detector, assuming ghosts exist and, for some reason, have electric charge.  Ok, this is a changing charge detector.  If a ghost disturbs the electric field in the vicinity of this gadget you will see the results on the LEDs.  Don't hold your breath, unless you wish to become a ghost yourself.  There's a pair 'a normal LEDs that display whether the charge at the antenna is changing in a positive or negative direction  (green vs red) . __ Contact: Charles Wenzel of Wenzel Associates, Inc.

Charge Your Mobile Device via Text Message  -   9-Apr-13 -Design News:   Elizabeth MontalbanoI recently wrote about a company developing a soccer ball that could harvest enough energy to recharge a mobile phone or power a light in a place where electricity is scarce.  Now I've learned of another project that also aims to provide energy in electricity-poor regions, this time targeting mobile __ Gadget Freak

Chase the Stars with a Camera  -   11-Mar-10 -Design News:   Who hasn't looked at the night sky and asked in awe, "How can I capture that?" A motor-driven star tracker won't let you grab a star, but it will let a camera track the movement of the stars so you can take spectacular photos.  The trick involves setting the proper tracking rate and pointing the __ Gadget Freak-Case #160

Cheap Close-Up Camera Lens  -   I often use my digital camera to take photos of some electronic projects.  At times, I need to get in close to capture some details.  But, without some additional optics, my camera just could not maintain focus, as I received closer to an object.  Being a cheap . . . Hobby Circuit designed by David A. Johnson P.E.-April, 2005

Check Out What Went On During National Robotics Week 2015!  -   10-Apr-15 -Design News:   Jennifer CampbellIn case you missed it, here are the highlights from National Robotics Week 2015 .  National Robotics Weeks Hits the STEM World Trading Cards Celebrate Robot 'All-Stars' 15 Robots That Project a Human Vibe igus Celebrates National Robotics Week at the Robot Block Party Industrial Robots Are Changing __ Gadget Freak

Chicken Coop Door Opener with Timer  -   I received an email from a guy in Australia who was trying to build a chicken coop system.  He was planning on using a conventional garage door mechanism to open and close the 6 doors to the coop.  The commercial door opener opened and closed the doors with a single pushbutton.  He wanted to install a standard 220vac powered timer so he could open the doors in the morning and close them at night. . . Circuit by David Johnson P.E.-March, 2013

Christina and the Dangerous Duck Slalom  -   21-Nov-05 -Design News:   To light the way home after a late night cramming at the library, Christina and friends designed this smart bike light.  Using two microcontrollers and powered by a battery pack that mounts to the bike's down tube, the device monitors both the bicycle speed  (via Hall Effect magnet) and amount of __ Gadget Freak

Christmas Tree Moisture Monitor  -   Originally intended to monitor the moisture in a potted plant, this moisture monitor really shines as a Christmas tree stand water level monitor! A fresh Christmas tree drinks water an annoying rate and bending down under the __ Contact: Charles Wenzel of Wenzel Associates, Inc.

CityHome Transforms Your Studio Apartment  -   1-Jul-14 -Design News:   Cabe AtwellIf you live in a major city, you know just how expensive the real estate can be.  Getting something "affordable" often means a studio apartment with barely enough space for you, let alone a roommate and/or a dog.  What can we do to make our humble abodes seem larger? MIT Media Lab's Changing Places __ Video-Gadget Freak

Click Sound Generator  -   Often in computer controlled systems, you would like to generate a “click” sound whenever a button is pressed.  This provides the user with audible feedback that the pushbutton press has been acknowledged.  The two circuits below generate such a sound.  A click sound is generated each time the logic input swings from a logic low to high condition. . . Circuit by David Johnson P.E.-January, 2009

Clive Dabbled in the Performing Arts  -   7-Mar-05 -Design News:   Tired of competing with his own artwork, Glasgow native and stage actor Clive Mitchell threw out the microcontrollers and discrete oscillators he once used to produce highly animated art pieces.  Designed to be displayed in a frame, his latest creation consists of a passive grid of low-intensity __ Gadget Freak

Clive Emitted That Youthful Glow  -   21-Feb-05 -Design News:   Committed to a cleaner environment, Clive recycles plastic objects into funky jewelry-perfect to wear for a night out clubbing as long as you don't mind lugging along a power supply! First, he glues colored LEDs into holes he has drilled into an array of clear plastic objects-the more varied the __ Gadget Freak

Cockroach Zapper  -   Using a PIC for this device provides a lot of useful functionality.  The timing for the power pulse to the inductor is critical to getting the best Zap from your nine volt battery.  The longer the current is on, the higher the voltage.  Once the inductor reaches saturation, however, you are just waisting power.   __ Designed by Luhan Monat-Mesa Arizona

Coin Operated Telescope  -   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.. . . Circuit by David A. Johnson P.E.-January, 2010

Color Film Makes Optical Filter  -   This isn’t 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. . . Circuit by David A. Johnson P.E.-January, 1998

Combination Lock  -   a digital lock with keypadenter the correct code to operate a solenoid.  Based around ua3731 __ Contact: P. Townshend EduTek Ltd

Combination Lock2  -   a digital lock with switches.  A nifty circuit i'm chuffed with, based around just 2 logic ics! __ Contact: P. Townshend EduTek Ltd

Come in Spinner  -   No, its not our version of Two-Up! Instead, you spin it and it writes messages in thin air.__ SiliconChip

Controlling the Rocket Fire  -   8-Aug-08 -Design News:   William Grill created a gadget that helps control the firing of model rockets.  The device provides basic rocket igniter functions, including an igniter “fuse” monitor, audio input and an LED display.  The gadget also features a “DeadMan” button  (which helps avoid an unintended launch) and a “Fire” __ Gadget Freak-Case #124

CopterBox Puts a New Spin on Air Cargo  -   13-Aug-07 -Design News:   Air delivery of supplies to areas where there's no place to land is typically done by parachute or helicopter.  A parachute is reusable, but requires a trained rigger, periodic inspection, occasional repairs, controlled storage conditions and, of course, some way to return it to base after the drop __ Gadget Freak-Case #106

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. . . Circuit by David A. Johnson P.E.-February, 2010

Courtesy Light Delay for Cars  -   Simple circuit has an adjustable delay from 7-40s and fades the lights out at the end of the delay period.  And the same circuit suits all cars.__ SiliconChip

Craig Was a Diehard Dashboard DIYer  -   9-Jan-06 -Design News:   When Craig discovered his local BMW dealer charges $50 to reset the oil change indicator light on his 1999 BMW 528i, he did what any good engineer would do.  He built his own reset tool.  The simple, money-saving tool is essentially a wire with a pin on one end, a clip on the other, and a resistor in __ Gadget Freak

Craig Wasn't a Particularly Well-Grounded Individual  -   5-Apr-04 -Design News:   An engineer who likes to collect data everywhere he goes, Craig figured out how to mount a speedometer that uses a Hall-effect sensor on his 42-inch-long skateboard.  By calibrating it for the 65-mm old-school wheels, he now knows his current speed, average and max speed  (30 mph!) , trip miles, and __ Gadget Freak

Craig's Simple Circuit Way to Generate a Split Supply  -   Wall plug transformer low wattage linear power supplies  (hereinafter known as WallWarts) are available cheaply , as surplus, from various online electronics component suppliers.  Typical price is $4 to $7 for a 12VDC, 5W part.  These make great line isolation and voltage reduction platforms for all sorts of useful power supplies.  A $1 three terminal regulator and 3 capacitors will make a nice DC power supply __ Contact: Charles Wenzel of Wenzel Associates, Inc.

Crazy Idea about Transformer II  -   I was building a simple amplifier as a reference monitor for my studio.  I had a hard time finding a suitable power transformer locally.  I needed something around +35 volts to ground and -35 volts to ground.  Dreading the thought of having one specially made or even making one myself, I got this crazing idea.   __ Designed by Jon Tirone, AKA John Fisher

Cricket Chirping Generator  -   Funny gadget for props and jokes.5, 12V Battery operation.   __ Contact: Flavio Dellepiane, fladello @ tin.it

CT 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 . . . Hobby Circuit designed by David A. Johnson P.E.-February, 2010

Cuckoo-song Generator  -   This circuit generates a two-tone effect very much alike the cuckoo song.  It can be used for door-bells or other purposes thanks to a built-in audio amplifier and loudspeaker
Used as a sound effect generator it can be connected to external amplifiers, tape recorders etc.  In this case, the built-in audio amplifier and loudspeaker may be omitted and the output taken across C8 and ground.   __ Contact: Flavio Dellepiane, fladello @ tin.it

Curtain Opener  -   Open or close the curtains of your house at the press of a switch.  All you need is this electronic curtain opener.  Meant for domestic use, especially for small doors and...__ Electronics Projects for You

Curve Fitting for the HP 35s Programmable Calculator  -   Programmable Calculator Software

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Gadgets:  #'s - C        D - E        G - L        M - O        P - S        T - Z


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