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Gadgets Circuits

Last Updated on: Friday, April 25, 2008 05:09 PM
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 got closer to an object. Being a cheap person, I didn’t want to spend money on an expensive close-up lens...

 

  • Homemade Corner Cube Reflector Using Glass Mirror Tiles
    Corner cubes are optical devices which have a unique property.  Light sent into the front face will be sent back to the source in a parallel path.  As long as light can strike the reflective surfaces the it will always be sent back to the source.  Tiny corner cubes can be molded into plastic for form an array of individual reflectors.  These are often used on bicycles to make them stand out at night....
  • Pigeon Scarecrow
    I have an area on my roof where a large flock of pigeons like to roost.  Their nesting materials and droppings really make a mess. Often there is enough junk from them that it clogs my roof gutters.  Perhaps one way to scare them away is with a device mounted on the roof near their favorite roosting spot.  The device....

  • Modified LED Night Light   NEW
    The circuit uses the classic series capacitor method to produce a current limiting LED driver, powered from the AC line.  The series capacitor forms a constant current source and will route the same amount of current through the parts, even if 3 or 30 LEDs were used in series.  This type of circuit made it much easier to insert 10 series wired LEDs instead of the three original devices.  I also switched from a NPN darlington driver circuit to a single n-channel FET. This made it easier to select the right resistor value to turn off the light in the day.  I set the required CdS cell resistance at about 100K, so anything less than that in resistance should keep the LEDs turned off.  I did have to change the resistor R2 to a 39v zener diode, to limit the peak voltage across the filter capacitor C1, when the LEDs are turned off during daylight. 

  • Shake to Charge Flashlight    NEW
    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 5.5 volt rating. I noticed that that this kind of super capacitor was originally designed for maintaining data in memory chips and has a rather high internal equivalent series resistance. This reduces the overall efficiency, since the device can’t be charged or discharge very quickly. Some of the power that should go to the LED will end up being dissipated inside the capacitor. Better super capacitors do exist.
  • Ocean Wave Power Generator Demo Unit
    A while back, a Discover Circuits visitor wanted a simply way to demonstrate how electricity could be generated from the up and down movement of ocean waves. The system was to be part of a science fair project, showing different renewable energy sources.  I gave this some thought and came up with the system shown below. It uses a simple plastic foam float attached to a lever arm,...
Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:

Avoiding Doggus Interrupt-Us:  Gadget Freak:  Planning a romantic evening at home? Les designed a remote control door opener so you don’t have to manually let Fido out of his cage. The system consists of a clevis mounted to the shaft of a solenoid and the door latch of the cage…. (added 2/07)

Bill Bowden: Night Rider:  Gadget Freak Case #94: Bill's got a bright idea for how to safely ride your bike in the dark…. (added 2/07)

Bob Solved His Chip Problem:  Gadget Freak Case #98 - Bob Neidorff's souped-up shop vac gadget cleans up after wood chip messes even a woodchuck would shun…. (added 2/07)

Craig Was a Diehard Dashboard DIYer:  Gadget Freak:  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…. (added 2/07)

Dick Had a Cameo Role in Scream 2:  Gadget Freak Case #102: Give the little witches and warlocks a real trick when they come clamoring for treats on Halloween with this doorbell-activated soundtrack. All that's required to build this spooky sound generator ….(added 2/07)

Dick Keeps His Home Fires Burning:  Gadget Freak Case #95: Last December it looked a lot like Christmas at Dick Neubert's home. Try his flicker bulb gadget for that "home for the holidays" feel.…. (added 2/07)

Dick Worked the Graveyard Shift:  Gadget Freak Case #91: When the local church needed storm effects for a skit, sound man Dick Neubert found the thunder on the Internet and added “lightning” with a photoflash strobe. He used an uncommitted output from the mixing board to trigger the strobe with the sound signal via a simple interface.…. (added 2/07)

Electronic Candle Blow Out:  LED or bulb switch off with a puff.  Funny gadget - 3V Battery supply (added 2/07)

Electronic Fuse:  Simple circuit that will protect your power supply from short circuits (circuit added 2/07)

Extra long-lasting Dripless Candles:  Gadget Freak:  A candlelight dinner? Relax and enjoy the lambent halos and silhouettes. With electronic flame flicker there's no hurry – the candles never burn down and they won't get wax on your tablecloth. But use real ones around the hot tub…. (added 2/07)

Fogger Smoke Machine:  (circuit / schematic design added2/07)

Hap Tells His Backyard Varmints to Hit the Road:  Gadget Freak Case #93: Tired of torn-up flower beds, Hap took matters into his own hands by combining a sprinkler and wireless driveway alert system. To allow enough time for the sprinkler valve to open, build pressure, and activate the sprinkler head, he constructed a time-delay unit from an old standby 555 timer…. (added 2/07)

Jared's Ride Isn't Fly But the Steering's Perfect:  So he always stays on course, Jared designed a mechatronic device that simulates perfect steering in an automobile. The small-scale, single-wheel model determines the speed of wheel rotation from the magnitude of the curve it's traveling….  Gadget Freak / Design News  (added 2/07)

Ken Put an End to Expensive Front-End Damage:  Gadget Freak Case #90:  Not satisfied with the low-tech method of suspending a tennis ball from a string, Ken Swanstrom devised a better garage locator device from a laser pointer. This simple circuit is powered by a 6V dc wall wort, adjusting the output to yield 3V dc as a substitute for battery power.....  (added 2/07)

Les Wears His Silicon On His Sleeve (UPDATED):  Gadget Freak Case #73:  Looking for cool way of wowing that special someone on Valentines Day/birthday/whatever? Build her a flashing heart made from LEDs driven by a programmable microcontroller. Les' gadget is simple to build and made from easily-obtainable parts. The unique thing about this design is the LEDs.... (added 2/07)

Nathan Loden: Glidden Special Forces Volunteer:  Gadget Freak Case #89: Looking to paint the town red (or his buddies at any rate), Nathan Loden devised this simple device to detect if the paintballs are traveling at a safe speed ( 300 ft/sec)….. (added 2/07)

Nick Has an Illuminating Flashback:  Gadget Freak Case #96: Nick Pagazani was tired of the limited range of his camera's flash, so he developed a slave trigger to help him brighten up his photos…. (added 2/07)

Our Everest Model has a Fireplace! (UPDATED):  Gadget Freak:  Bruce Field and daughter Ellie are happy campers, thanks to a portable heating/cooling device they built that maintains a constant, comfortable temperature inside their camping tent.…. (added 2/07)

Project Dragon Fish:  Gadget Freak Case #97: Joe Peck's exploration of underwater model rocketry brings him to new heights ... and new depths…. (added 2/07)

Resistor Calculator :  Luxeon Application Note  (app note added 2/06)

Salt Water Battery:  (electronic circuit added 2/07)

The Curious Incident of the Dog in the Night (UPDATED):  Gadget Freak:  Remote Control Dog Door Opener.  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 …. (added 2/07)

You Can Get Scrooged Opening a Trap Door:  Gadget Freak:  Ever try opening an attic door in the ceiling at the top of the stairs with your hands full of stuff? Try spelling headache! So Larry installed a 12V motor with a cable shaft in the attic and attached the cable to the door. Limit switches stop the motor when the door is fully open and closed, and a converter ensures the correct voltage.... (added 2/07)
 

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