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DiscoverCircuits.com -- Hobby Corner
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


Gated 125Khz Oscillator   -  This circuit is uses a NAND gate as an inverter.  The gate allows the oscillator to be gated on and off.  Again, the values shown set the frequency at 125KHz but can be changed to produce other frequencies . . . Hobby Circuit designed by David Johnson P.E.-March 12, 2002

Gated Crystal Oscillator with Very Low Power   -  The circuit gates the output of a continuously operating 32KHz crystal oscillator to the input of a C-MOS buffer when clock pulses are needed.  The technique gets around the problem of a slow starting crystal oscillator by keeping the oscillator going and switching on a transistor power stage only as needed . . . Hobby Circuit designed by Dave Johnson P.E.-June 03, 2000

Generate 0.5v Negative Supply   -  A while back someone needed a simple way to generate a negative 0.  5v supply from a conventional transformer type AC to DC power supply.  The circuit below uses a couple schottky diodes and a filter capacitor to perform the feat . . . Hobby Circuit designed by David A. Johnson P.E.-July 10, 2011

Generate Short Delayed Pulse   -  This circuit generates a short 10ms pulse 15 minutes after a ďstartĒ pushbutton switch is activated . . . Hobby Circuit designed by David Johnson P.E.-December 18, 2004

Ground Resistance Tester   -  UL requires that an electrical system using a metal chassis earth ground connection have a resistance of less than 0.1ohms.    This resistance must be tested with actual line current in excess or 10 amps.    The circuit shown uses a couple of LEDs to indicat . . . Hobby Circuit designed by Dave Johnson P.E.-April 28, 2001

H Bridge Motor Controller uses Low Power   -  This circuit uses a few logic gates & a 74AC240 to control power to a small gear motor . . . Hobby Circuit designed by David A. Johnson P.E.-July 13, 2006

Harvest Earthworms with this Electrical Device   -  When I was a kid my engineer uncle built a circuit similar to the one below.  My cousin and I used it to force earth worms out of the ground to be used for fishing.  It worked like a champ.  Please be careful since there is high voltage at the probe tips . . . Hobby Circuit designed by Dave Johnson P.E.-July 09, 2006

High Ambient Light Immunity Light Detector    -  The circuit below was designed to turn on an external 12v relay, whenever it detects light from a nearby LED light source, modulated at 40KHz to 50KHz.   This circuit was originally designed to operate from a fast moving vehicle . . . Hobby Circuit designed by David A. Johnson P.E.-July 11, 2006

High DC Current Indicator   -  A while back, someone requested a simple method to indicate when 20 to 50 amps of DC current was flowing through a wire.  The circuit below works well and is about as simple as you can get.  A sensitive reed relay . . . Hobby Circuit designed by David A. Johnson P.E.-April 01, 2005

High Impedance JFET Buffers   -  I have used these circuits many times.  They are great when you need a low gain AC signal amplifier with a very high input impedance.  It is good to beyond 50MHz . . . Hobby Circuit designed by Dave Johnson P.E.-July 11, 2006



High Speed Light Detector from FET Input   -  This circuit is yet another design that converts current from a PIN photo diode to a voltage.  It has a bandwidth that extends beyond 50MHz . . . Hobby Circuit designed by Dave Johnson P.E.-June 17, 2000

High Temperature Thermocouple activates Relay   -  Voltage from a high temperature thermocouple activates a relay when the sensor detects a temperature above 1000 degrees F . . . Hobby Circuit designed by David Johnson P.E.-July 04, 2006

High/Low Voltage Tester on AC Power Line    -  if you wish to test a line-powered device under both a 15% high and a 15% low voltage condition, you can use the circuit below.  The circuit uses an 18v transformer with a 3 amp rating.  A double pole, double throw toggle switch then switches in the . . . Hobby Circuit designed by David Johnson P.E.-March 14, 2010

Highly Stable Lower Power Oscillator   -  This circuit works much like the classic 555 timer, but draws only about 1.5 microamps from a 3 volt battery.  It is highly stable under varying temperature and supply voltages . . . Hobby Circuit designed by David Johnson P.E.-May 29, 2000

HO Model Train Lighthouse Flasher   -  HO train sets often have authentic looking scale model homes and buildings.  The hobby circuit below can be mounted inside a model lighthouse.  The electronic circuit drives a single LED lamp in such a way that it produces light which simulates the rotation . . . Hobby Circuit designed by David Johnson P.E.-July 11, 2006

HO 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.    iím still not 100% pleased but the revised circuit below seems to operate a bit better than the older circuit.  Ö [Hobby Circuit designed by Dave Johnson P.  E.  , May 2012] . . . Hobby Circuit designed by David Johnson P.E.-December 24, 2012

Home Made Geophone Detects Foot Steps   -  A home made geophone is made from a strong magnet, a coil of wire and a rubber band.  The circuit is sensitive enough to detect the vibrations of a nearby foot stomp.  It could be used as an earthquake detector.   . . . Hobby Circuit designed by David Johnson P.E.-June 02, 2006

Homemade Corner Cube Reflector   -  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 co . . . Hobby Circuit designed by Dave Johnson P.E.-January 00, 1900

Hot AC Power Line Indicator   -  The circuit below is designed to detect when a power cable is active (hot).  When the flat sensor end of the device is held near an active AC line, the bright green LED on the top of the housing will glow.  It is powered by a 3v CR2032 lithium coin cell.  I . . . Hobby Circuit designed by Dave Johnson P.E.-May 02, 2005

Hour Meter triggered by Machine Vibration   -  This hobby circuit allows an off-the-shelf battery powered digital hour meter to be turned on and off, according to a machine's operation, without requiring a direct electrical connection to the machine . . . Hobby Circuit designed by David Johnson P.E.-December 26, 1998

Ideal Diode for PV Panels   -  Solar panels usually include a diode at their outputs.  The diode prevents current from back feeding into the panel at night from the battery being charged by the panel.  But, this diode does waste some power and does reduce the available panel voltage . . . Hobby Circuit designed by David A. Johnson P.E.-January 26, 2009

Ideal Diode Function   -  Most photovoltaic solar panels are used to charge a battery during the daytime.  Nearly all panels come equipped with a blocking diode.  The diode prevents DC current from flowing backwards from the battery bank into the panel at night.  The usual blocking . . . Hobby Circuit designed by Dave Johnson P.E.-January 22, 2008

Illuminated 16vAC Doorbell Lamp Replacement     -  A while back I noticed that the lamp inside the illuminated pushbutton switch for my doorbell burned out.  I carefully removed the doorbell, opened the switch housing and then replaced the incandescent lamp inside with the circuit shown below.  The circuit uses two small but very bright green LEDs from King Bright.  The resistor sets the average LED current at about 3ma.  The diode prevents reverse biasing the LEDs.  The two lamps emit plenty of light and should last much longer than the incandescent lamp they replaced . . . Hobby Circuit designed by Dave Johnson P.E.-June 20, 2011

Improve Response Time of a Photo Transistor Circuit   -  This page shows different ways to improve the response time of a photo transistor circuit . . . Hobby Circuit designed by David A. Johnson P.E.-July 11, 2006

Improve the quality of standard TV images   -  I designed this circuit many years ago, based on the claims that the technique would improve the quality of standard TV images.  The circuit adds information to the edges of the objects and was reported to bring out more detail.  After building and testing . . . Hobby Circuit designed by David A. Johnson P.E.-July 08, 2000

Improved Solar Path Light   -  The circuit below was designed to replace the guts of an existing path light assembly with one which has a much better performance.  I suggest using a quality 10 cell solar panel with at least a 4 square inch area.  Buy a panel with solar panels that fills . . . Hobby Circuit designed by David Johnson P.E.-March 13, 2011

Increased power for LED Flasher   -  Power LEDs are becoming more popular these days.  The DC input power to these devices ranges from 1 watt to 5 watts.  Normal LEDs only receive about 0.  05 watts.  At this higher power, these devices can emit a lot of light . . . Hobby Circuit designed by David A. Johnson P.E.-8/0/2008

Indicate DC Current Flow   -  The circuit below is a simple way to indicate when DC current is flowing through a wire.  The circuit is designed so it will turn on a LED indicator light, whenever the voltage drop across a shunt resistor exceeds about 0.1volts.  The value of the resist . . . Hobby Circuit designed by David A. Johnson P.E.-October 16, 2005

Indicate Electrical Current with this Circuit   -  I designed this circuit as a simple current indicator for any load ranging from 40 watts to 250 watts.  The circuit turns on a small LED, whenever it detects current flowing to a remote load . . . Hobby Circuit designed by Dave Johnson P.E.-July 11, 2006

Indicates 120 VAC or 240 VAC   -  Two LEDs indicate if a power line has 120vac or 240vac voltage on it . . . Hobby Circuit designed by David A. Johnson P.E.-July 09, 2006

Indicates Automotive Electrical Voltage   -  When troubleshooting the 12v electrical system of an automobile, it is nice to have a simple voltage indicator tool instead of a voltmeter.  This electronic circuit, hobby circuit is powered by two AA or even two N cells, which will provide enough energy . . . Hobby Circuit designed by David A. Johnson P.E.-July 09, 2006

Indicates Battery Charge Current   -  This circuit turns on a LED whenever it detects at least 25ma of battery charge current . . . Hobby Circuit designed by Dave Johnson P.E.-July 23, 2006

Indicates Battery Charging Current   -  Anyone who has ever had a shocking experience on an especially dry day is acutely aware of the kinds of high voltage that can be generated from a simple walk across a carpeted floor.  Those same finger to metal sparks can destroy or disrupt sensitive elect . . . Hobby Circuit designed by Dave Johnson P.E.-January 23, 2011

Indicator for Acceptable Voltage   -  I have used this circuit many times in custom test fixtures where a simple go-no go indication was needed.  The circuit can also be used to adjust a particular voltage be within specific high or low limits.  The three LEDs will indicate if the voltage is . . . Hobby Circuit designed by David A. Johnson P.E.-February 09, 2002

Indicator for Bad Light Bulb   -  This request came from a Discover Circuits visitor.  He wanted to turn on a LED indicator light whenever a circuit detected a burned out tail/brake light on a car or truck.  The circuit shown below uses a transistor switch, to detect current flowing through a low value resistor . . . Hobby Circuit designed by David Johnson P.E.-December 17, 2006

Inductive Pulse Receiver (175Khz)   -  This circuit is discussed in more detail in the Experimenters Journal. The receiverís six inch diameter coil detects the ring signal from the above transmitter and use a single NPN transistor to provided enough amplification for the signal to be easily viewed on an oscilloscope . . . Hobby Circuit designed by Dave Johnson P.E.-July 09, 2006

Infrared Remote Extender Circuit   -  This circuit is designed to be placed directly in front of a standard TV or VCR remote.  The exiting light pulses produced by the circuit match the pulses from the remote but are about 10 times more powerful . . . Hobby Circuit designed by Dave Johnson P.E.-June 04, 2000

Inrush Current Limiter for a Incandescent Lamp    -  This circuit limits the large inrush current often associated with large incandescent lamps.  With the components shown the current is limited to 1 amp, but it could be scaled to any desired current . . . Hobby Circuit designed by Dave Johnson P.E.-July 09, 2006

Insolution_Meter_Solar   -  You donít need a fancy and expensive meter to measure the sunís intensity.  With some inexpensive parts you can build your own meter.  I used a 1ma meter movement and a single solar cell I got on eBay with an area of about one square inch.  I calibrated the meter on a very clear bright summer day when the sun was directly overhead. . . . Hobby Circuit by David Johnson P.E.-July 14, 2017

IR TV/VCR Remote Booster   -  This circuit will boost the signal from any infrared TV or VCR remote, extending the range by a factor of 3X.   . . . Hobby Circuit designed by David Johnson P.E.-October 05, 2005

Isolated Miniature AC/DC Power Supply   -  This circuit uses a novel approach to produce a fully isolated and regulated 5 volts @30ma from the 120vac power line.  It uses two tiny SCRs that alternately discharge two capacitors through a miniature high frequency transformer . . . Hobby Circuit designed by David A. Johnson P.E.-June 09, 2000

It's Time to Dust Indicator   -  I thought about this circuit when I heard that a lot cleaning personal in hotels were either dusting rooms more often than necessary or not enough.  I have not yet built and tested this circuit completely but in concept it should work . . . Hobby Circuit designed by David A. Johnson P.E.-July 06, 2000

Knocking rings Doorbell   -  in some apartment buildings and homes, not equipped with a door bell, it may be hard to hear someone knocking on the front door.  The circuit below provides a means to activate a loud beeping sound inside, whenever someone knocks on the door . . . Hobby Circuit designed by David A. Johnson P.E.-June 14, 2009


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


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