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Last Updated on: Thursday, December 07, 2017 02:05 PM

Hobby Circuits List

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Hobby Circuits designed by David Johnson
Circuit Name and Description

#'s          A         B - C          D - F        G - K          L          M - O          P - R         S - Z


Mason_Jar_Solar_Light   -  I have modified several commercial solar garden lights over the years.  I switch out the LED, solar panel, battery pack and control circuit.  The result is a much better overall light.  One of my disappointments in using store-bought garden light assemblies is their construction.  They are built so cheaply that over time, water and insects get inside, killing the light operation. . . . Hobby Circuit by David Johnson P.E.-September 21, 2017

Measure Button Battery Cell's Internal Resistance    -  The open cell voltage of a small silver oxide button cell battery remains very close to 1.5 volts over most of the life of the cell.  However, there is a relationship between battery health and the internal resistance of the cell.   This circuit when used . . . Hobby Circuit designed by David A. Johnson P.E.-July 11, 2006

Microphone On/Off Switch Circuit is Pop Free   -  This circuit uses a simple technique to eliminate the usual “pop” sound when an electret type microphone is switched on or off.  The circuit is completely passive and will work on dynamic and electret type microphones . . . Hobby Circuit designed by Dave Johnson P.E.-February 15, 2002

Miniature Pushbutton On/Off Switch   -  in many battery powered devices, you would like to turn the circuit on and off by pressing a small pushbutton switch.  One press turns the device on and second press turns it back off.  The flip/flop circuit below uses a minimum number of parts to perform . . . Hobby Circuit designed by David Johnson P.E.-October 16, 2005

Model Airplane Wing Tip Flasher   -  The circuit below is designed to flash two white LEDs mounted at the wing tips of a model airplane.  The flasher unit is powered by a 4.  5v supply made of three AA or AAA 1.5v alkaline battery cells.  The average current is about 2ma so a set of batteries . . . Hobby Circuit designed by David A. Johnson P.E.-October 15, 2009

Model Train Lighthouse Flasher   -  HO train sets often have authentic looking scale model homes and buildings.    A while back someone asked me to design a flashing LED light, which he could mount inside a model lighthouse and have it operate so it would appear to rotate and flash.    I designed a working circuit but I was never pleased with the results.    i’m still not 100% pleased but the revised circuit below seems to operate a bit better than the older circuit.  … [Hobby Circuit designed by Dave Johnson P.  E.  , May 2012] . . . Hobby Circuit designed by David Johnson P.E.-December 24, 2012

Model Train Lighthouse Flasher Revisited   -  This was originally designed for a model in a HO train set.  It simulates the behavior of the light from a lighthouse.  The LED intensity gradually increases, then flashes with a bright light and finally decreases slowly in intensity . . . Hobby Circuit designed by David Johnson P.E.-December 24, 2012

Model Train Lighthouse Flasher Revisited   -  HO train sets often have authentic looking scale model homes and buildings.    A while back someone asked me to design a flashing LED light, which he could mount inside a model lighthouse and have it operate so it would appear to rotate and flash.    I designed a working circuit but I was never pleased with the results.    i’m still not 100% pleased but the revised circuit below seems to operate a bit better than the older circuit.  … [Hobby Circuit designed by Dave Johnson P.  E.  , May 2012] . . . Hobby Circuit designed by David A. Johnson P.E.-December 24, 2012



Modified LED Night Light   -  I bought some night lights a few months ago from Walmart here in Denver.  The devices were made by Elumina Lighting Technologies inc. (www.  eluminalighting.  com) , their model LED-6200A.  I think I paid about $15 for a pack of three lights.  I wanted a light . . . Hobby Circuit designed by David Johnson P.E.-May 21, 2007

Modified Shake to Charge Flashlight   -  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 . . . Hobby Circuit designed by David A. Johnson P.E.-January 01, 2012

Modulated Light Receiver Front-End Circuit   -  This circuit uses a unique cascode amplifier circuit to convert the current from a PIN photo diode to a current without any feedback network.  It is very stable and very sensitive.  This hobby circuit shown has the potential for a conversion factor of 10 volts per microwatt at 900nm.  I included a simple JFET post-amplifier with a gain of about 20.   . . . Hobby Circuit designed by David Johnson P.E.-March 12, 1999

Modulated Light Receiver uses a Single IC   -  The circuit uses a very inexpensive C-MOS IC that is connected to a small photodiode.  Using a unique inductive feedback network, the circuit provides high sensitivity under high ambient light conditions.  It is a great circuit when you want to extend the range of an optical remote control transmitter . . . Hobby Circuit designed by David A. Johnson P.E.-June 04, 2000

Momentary Touch Activated Switch   -  A single 1.5v silver oxide button cell powers this complete touch activated switch circuit for 5 years.  It features both a normally open and a normally closed set of solid-state switch thermals.  It also has an adjustable sensitivity, which can be set for a touch capacitance change as small as 1 picofarad.   . . . Hobby Circuit designed by Dave Johnson P.E.-January 18, 2002

Monitor ON/OFF status of a Remote Switch   -  There are many applications when a remote switch’s on/off status needs to be monitored.  Reed relay sensors, toggle control switches and security alarms contacts are just a few examples.  Routing a switch directly to a computer system hundreds of feet away . . . Hobby Circuit designed by Dave Johnson P.E.-January 04, 2009

Monitor Water Seepage   -  A while back I received a request from a company who needed a water seepage detector.  They wanted a device that ran on 24vac and detected water using a fully isolated circuit.  They wanted a circuit which switched off 24vac to a load when water was detected . . . Hobby Circuit designed by David A. Johnson P.E.-January 16, 2011

Monitors AC Current   -  This circuit uses a small AC current transformer from Magnetek to produce an isolated voltage proportional to the AC current in the primary winding.  The transformer contains a single turn primary with a low 0.  001-ohm resistance.  It can easily handle 30 . . . Hobby Circuit designed by David Johnson P.E.-July 10, 2006

Motorized Duck Decoy Timer   -  I received a nice email from a duck hunter.  He uses some motorized decoys to lure ducks into his line of fire.  However, the battery powered decoys only have an on/off switch so once turned on; the decoy flaps its wings or paddles around continuously.  The hunter wanted a more realistic motion, which would power the motor for say 10 seconds, then stop for another 10 seconds before starting up again.  The simple circuit below should work well for his application . . . Hobby Circuit designed by David A. Johnson P.E.-August 30, 2011

Moving AIR Indicator   -  Many months ago a Discover Circuits reader wanted a method to indicate when a fan was blowing air.  He didn’t want to route any electrical wires to a sensor near the fan.  Instead he wanted all the electronics for both the fan and other circuits mounted s . . . Hobby Circuit designed by Dave Johnson P.E.-August 16, 2006

Negative 0.5 Volt Supply   -  This simple circuit consists of two LEDs and a photo diode.  It generates a negative voltage with a current level of a couple milliamps.  It is ideal for supplying a negative rail to low power “rail to rail” op amp circuits, which need to have a true zero volts output.  Note:  This circuit is not particularly efficient . . . Hobby Circuit designed by David Johnson P.E.-July 13, 2006

Next-Generation Star-Trek Doorbell   -  in the Star Trek “Next Generation” TV series, the doorbell outside the private quarters of a crew member makes a particular “beep-boop” sound.  The 3v battery powered circuit below tries to simulate this sound.  The circuit uses one 74HCT74 dual D flip/flop . . . Hobby Circuit designed by Dave Johnson P.E.-October 12, 2001

Night_Light_with_20_LED   -  After 3 years of continuous 24/7 operation I noticed that the 20 LED array I was using as a night light next to my back door was fading.  Some of the LEDs were much dimmer than others.  I figured that over time, the internal heat dissipated from the LED chip was causing the LED light intensity to fade.  I decided it was time to replace the light. . . . Hobby Circuit by David Johnson P.E.-July 24, 2017

Nitrogen Spark Generator   -  Nitrogen or air sparks are very powerful light sources that produce flashes that last only a few nanoseconds.  This line powered circuit generates a continuous series of very small sparks across electrodes with a 0.  05 inch gap . . . Hobby Circuit designed by Dave Johnson P.E.-June 04, 2000

NMH/NiCd 6v Battery Tester   -  I designed this circuit to test rechargeable six volt battery packs under constant current conditions.  As designed, the circuit applies a 10 amp load to the battery pack.  A heat sink must be used on the main power transistor . . . Hobby Circuit designed by David A. Johnson P.E.-December 12, 2004

Noise_Generator_using_Mm5437   -  Many years ago National Semiconductor came out with a neat white noise generator IC.  They are no longer being made but they can still be found on eBay.  This little 8 pin part is very easy to use.  It draws about 4ma of current and can operate over a range of 4.5v to 11.5v.  It might even operate down to 3v. . . . Hobby Circuit by David Johnson P.E.-July 30, 2017

NPN/PNP Transistor Tester   -  I designed this circuit about 30 years ago and still use it from time to time.  It is powered from a 3v battery.  It makes a tone when the transistor tests good.  It can be used to determine device type (NPN or PNP) and the base, collector or emitter transist . . . Hobby Circuit designed by Dave Johnson P.E.-June 28, 2000

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 . . . Hobby Circuit designed by David Johnson P.E.-January 00, 1900

One Amp Current Injector   -  I designed and built this thing many years ago.  I published the hobby circuit in the now defunct Radio Elecronics magazine back in 1992.  The electronic circuit injects a precise 1 amp of current into any unknown resistor, up to about two ohms.  Two alkaline . . . Hobby Circuit designed by David A. Johnson P.E.-July 11, 2006

One Nimh Cell powers White LED   -  There are a lot of white LED driver circuits floating around.  A popular circuit called the “Joule Thief” can drive one white LED from a single 1.  2v or 1.5v battery cell.  Most of these circuits use one or two transistors to form a voltage boost circuit . . . Hobby Circuit designed by Dave Johnson P.E.-September 26, 2009

Oneshot & Latch Pushbutton   -  This circuit uses a single IC to convert a noisy pushbutton switch signal into a clean pulse or a sustained push on-push off signal.  It can operate from 3v to 18v . . . Hobby Circuit designed by David Johnson P.E.-March 26, 2002

One-Watt White LED Night Light   -  As many of you know, I have a pet peeve with poorly made LED night lights.  Often, the light from the LED quickly fades, so within months, the light is useless.  I have posted several versions of modified night lights using higher quality components.  This circuit is yet another version, which produces much more light than those other designs.   . . . Hobby Circuit designed by David A. Johnson P.E.-November 06, 2008

Operation of Cascode Light Receivers   -  This page provides a detailed explanation of how the modified cascode light receiver circuit operates.  The cascode technique in conjunction with an inductive load provides very high current to voltage conversion as well as very high speed . . . Hobby Circuit designed by David Johnson P.E.-February 15, 2002

Optical Fiber Receiver-5Mhz Broad Band   -  This circuit is a simple broad band light detector that uses a very inexpensive IC and a PIN photodiode that is packaged for use with plastic optical fibers.  It has a bandwidth from 1KHz to over 5MHz.  It is great for experimenting with various modulated . . . Hobby Circuit designed by David Johnson P.E.-June 04, 2000

Optical Filter using Color Film Negative   -  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 . . . Hobby Circuit designed by David A. Johnson P.E.-January 01, 1998

Oscillator Draws 2 Nanoamps   -  if you have hundreds of touch switches that need an excitation signal, then this circuit is what you need.  Its 20KHz 20v peak to peak output signal can supply up to 3 watts of touch switch excitation power . . . Hobby Circuit designed by David A. Johnson P.E.-July 11, 2006

Oscillator with Ultra Low Current   -  Here is a challenge.  Design an astable oscillator which draws only a few nanoamps of current from a +3v supply.  I gave this some thought and came up with the circuit below.  I used some pretty standard parts except for three surface mounted 1000M resist . . . Hobby Circuit designed by David A. Johnson P.E.-March 08, 2009

Over-Temperature Micro-Power Alarm   -  The circuit is powered for years by a single 3 volt lithium battery.  It sounds an alarm when the temperature exceeds a certain point.  With some minor changes the circuit could also be configured for an under temperature (freeze) alarm.  The circuit uses a . . . Hobby Circuit designed by David Johnson P.E.-June 04, 2000


#'s          A         B - C          D - F        G - K          L          M - O          P - R         S - Z


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