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Gadgets Circuits
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Last Updated on:
Thursday, October 30, 2014 09:22 AM

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....


Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:
A Fish Caller -  Click and click may not sound like much, but to a fish is it a dinner bell….(Circuit design added 12/08) [designer unknown]
A Matrix Multi-Tool for the HP 35s Programmable Calculator -  Programmable Calculator Software added 03/09
An SCA Adapter -  Subsiduary Communication Authorization. For Advertisement Free Background Music on FM. This applies to an Additional 67 Khz Modulation on the standard FM Carrier.  It is intended to provide Commerical-Free Background Music for Stores, Offices and others.....(Circuit design added 12/08)
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.....(added situlator 03/09)
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.....

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)
Battery Desulfation/Tester. -  This circuit helps to Desulfate Lead Acid batteries.  Added Bonus:This Circuit also gives a good indication of the Internal Resistance of the battery.....(Circuit design added 12/08)
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)
Breadboard as Hotplate -  A standard 60 mm x 100 mm piece of prototyping strip board (breadboard) can very simply be used as a 12 V warming plate. All that’s necessary is to connect the copper tracks in series. At 12 V the board will pass around 4 A giving a power dissipation of almost 50 watts.….must register on this site.... [Published in Elecktor July/August 2010]
Cat Detector for a Cat or Dog Flap on a 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  ….(Circuit design added 3/08)
Cat Toy -  The PIC12F675 is small in size and low in power. It lends itself to some really off-beat uses..... [Luhan Monat - Mesa Arizona]
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..... [Hobby Corner Circuit by Dave Johnson]
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)
Craig's Simple 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.....(electronic design added 6/07)
Cricket Chirping Generator -  Funny gadget for props and jokes.  5, 12V Battery operation.  (circuit added 6/07)
Curve Fitting for the HP 35s Programmable Calculator -  Programmable Calculator Software added 05/10

Gadget Circuits:  # - C       D - E      F - L      M - N      O - S      T - Z


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