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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


Dark Activated 12v Power Supply Switch   -  Using an inexpensive phototransistor, this circuit switches 12v to 24v power to a load, whenever the sun goes down . . . Hobby Circuit designed by Dave Johnson P.E.-July 09, 2006

DC Brushless Motor Monitor   -  The circuit below was requested by a person needing a way to keep track of the number of hours a 24v DC brushless motor was in operation.  The circuit taps into a bit of the power going into the motor using a bridge rectifier and filter capacitor.  The voltage produced feeds the input of a small solid state relay.  The output of the relay routes AC power to an hour meter, every time the brushless motor is turned on.  This same circuit could be used with other DC motors with some simple modifications . . . Hobby Circuit designed by Dave Johnson P.E.-April 01, 2005

DC Current Bidirectional Indicator   -  This circuit is handy for battery powered systems.  The circuit is self-powered using a single 3v lithium coin cell.  The current draw is so low that the battery should last for years.  The hobby circuit flashes a red LED when DC current is drawn from the battery and flashes a green LED whenever current flows into the battery.  Two “probe” input wires connect across a section of cable, which acts as a shunt resistor.  A voltage of only 5mv in either direction will trigger a LED indication . . . Hobby Circuit designed by Dave Johnson P.E.-March 31, 2011

Demo of a Wave Power Generator System   -  An inexpensive stepper motor is used as a voltage generator in this wave generator demo.   . . . Hobby Circuit designed by Dave Johnson P.E.-July 27, 2003

Detect Clear Fluid   -  This circuit detects when a clear fluid is inside a piece of clear plastic tubing.  It can be used for fluid level control and monitoring . . . Hobby Circuit designed by Dave Johnson P.E.-July 11, 2006

Detect Motion with a Piezo Device   -  Using a piezoelectric device, this circuit will activate a beeper whenever the circuit is moved.    it could be used as an earthquake alarm.   . . . Hobby Circuit designed by Dave Johnson P.E.-July 09, 2006

Detect RF Signal at 2.45GHz   -  Many cordless telephones, computer networks and cell phones use a RF transmitter lefted on the 2.  45GHz band.  Using a microwave diode detector and 100uA meter, this passive circuit will display the strength this signal.  The drawing shows how a bent piece of wire can be used as the antenna.   . . . Hobby Circuit designed by Dave Johnson P.E.-July 09, 2006

Detect Short Xenon Lamp Flashes   -  This circuit uses a small 2.5mm square photo diode in conjunction with a 100mH coil to detect the short light flashes from a xenon lamp.  The coil makes the circuit immune to normal room lights.  Its 10mv sensitivity can detect light flashes from a range of over 100 feet.   . . . Hobby Circuit designed by Dave Johnson P.E.-February 15, 2002

Detector for Human Footsteps   -  This circuit uses a surplus geophone to detect human footsteps from 100 feet away.  It was designed for monitoring the Mexico/USA border.  This preamp part of the system draws about 50 micro amps from a 12 volt supply . . . Hobby Circuit designed by Dave Johnson P.E.-July 11, 2006



Detector/Switch for Audio Signal   -  For some audio systems it is desirable to have an automatic switch circuit turn on other devices, such as an amplifier, if an audio signal is detected on one line.  The hobby circuit below will activate a transistor switch when it detects at least 50mv peak to peak of an audio signal.  The switch could be used to turn on a relay, routing the signal to where it is needed.  A single 3v lithium cell will power the electronic circuit for about 5 years . . . Hobby Circuit designed by David Johnson P.E.-July 09, 2006

Detects Low Voltage 120VAC Power Line    -  This hobby circuit will turn on a beeper when the line voltage drops below 100 volt AC . . . Hobby Circuit designed by Dave Johnson P.E.-July 09, 2006

Detects Xenon Lamp Flash   -  This circuit has a very low standby current requirement yet has very high sensitivity toward the light flashes from a xenon lamp.  When connected to a flip/flop it can serve as an on on/off Controller . . . Hobby Circuit designed by David Johnson P.E.-December 14, 2004

Digital Counter using Pedometer   -  There are many occasions when you may want to count something electronically.  Perhaps it is car traffic on a street or items moving down an assembly line.  It might be the number of times a machine is activated or maybe you want to count the number of . . . Hobby Circuit designed by David Johnson P.E.-August 17, 2008

Digital noise generator   -  When you need to test an audio circuit with broadband noise, this circuit works great.  It uses just three inexpensive C-MOS ICs  that generate a series of output pulses whose widths vary randomly.  I included a level control pot . . . Hobby Circuit designed by David A. Johnson P.E.-July 04, 2000

Display RF Signal Strength   -  Many cordless telephones, computer networks and cell phones use a RF transmitter lefted on the 2.  45GHz band.  Using a microwave diode detector and 100uA meter, this passive circuit will display the strength this signal.  The drawing shows how a bent piece of wire can be used as the antenna.   . . . Hobby Circuit designed by David Johnson P.E.-July 09, 2006

Divide a TTL Clock Signal by 1.5   -  Two inexpensive ICs  divide a TTL clock signal by 1.5.  By following the circuit with another flip/flop, you could also generate a divide by three function . . . Hobby Circuit designed by David Johnson P.E.-July 06, 2000

DIY Cell Phone Charger   -  It seems that as cell phones become more sophisticated, their operating times become shorter and shorter.  If you are on the go all the time and have difficulty finding AC or DC outlets to charge your phone, you might consider this simple scheme . . . Hobby Circuit designed by David Johnson P.E.-June 04, 2000

Doorbell heard in Basement   -  if you can't hear your doorbell when you are in your basement try this circuit.  This circuit takes advantage of the 24vac power source located near the furnace.  Using a simple current transformer technique, the circuit sounds a beeper whenever the . . . Hobby Circuit designed by David A. Johnson P.E.-June 04, 2000

Drive a LED with an Intensity Ramping Mode   -  The circuit below was designed to drive a LED with an intensity ramping mode.  Two 555 timers generate two different triangle waveforms.  The upper device generates a 10KHz signal while the lower unit produces a 1Hz signal.  The two signals are fed to a . . . Hobby Circuit designed by David Johnson P.E.-December 21, 2007

DVD Recorder + TV Camera Make Cheap Data Logger   -  Sometimes recording the results of a test requires as much ingenuity as designing the product.  Consider a situation which requires the collection of many different variables over a long period of time . . . Hobby Circuit designed by David A. Johnson P.E.-April 01, 2005

Earthquake Alarm Circuit   -  Geophones are dandy motion sensors.  They are metal cans containing a powerful magnet, suspended with springs inside a coil of wire.  The magnet functions as a floating mass.  The slightest vertical motion of the device causes the coil to move relative to . . . Hobby Circuit designed by David A. Johnson P.E.-July 08, 2005

ELC signal between 200Mhz-400Mhz   -  if you need a clean emitter coupled logic (ECL) type signal between 200MHz and 400MHz this circuit works fine.  It uses four voltage-controlled capacitors to change the frequency . . . Hobby Circuit designed by David A. Johnson P.E.-June 03, 2002

Exciter Circuit-12v Touch Switch   -  This circuit generates a 20KHz pseudo sine wave signal that can power approximately 50 remote touch activated switch circuits.  This hobby circuit can support a cable length of approximately 2500 feet.  A typical remote switch circuit is also shown as . . . Hobby Circuit designed by David Johnson P.E.-February 10, 2002

FETs & Logic Devices Divides Supply Voltage on Charge Pump Efficiently    -  This circuit uses a few FETs and logic devices to down convert a DC voltage to about one half its value . . . Hobby Circuit designed by David A. Johnson P.E.-July 08, 2000

Finger Tap Piezo Relay   -  This circuit uses a flat piezo wafer, glued inside a plastic box, as a finger tap sensor.  With each tap of a finger to the box holding the wafer, the circuit turns on and off AC or DC power to an external device.  The circuit is powered by a 9v 9v battery . . . Hobby Circuit designed by Dave Johnson P.E.-November 07, 2010

Fireflies_In_Jar_Solar_Light   -  When I was a kid, growing up in Illinois, I remember catching fireflies and putting them into a jar.  I loved watching them flashing away at night.  Later, I would let them out to live another day. . . . Hobby Circuit by David Johnson P.E.-September 21, 2017

Flasher_&_Beeper_for_Well_Pump   -  Several years ago I installed a box on my water well pump head.  At the well head, the solar powered box flashed a very bright LED light and chirped a very load siren, whenever the pump motor was in operation.  After many years of service, the box finally became corroded from rain water and died.  So, I thought it was time to redesign the circuit and build up a replacement. . . . Hobby Circuit by David Johnson P.E.-June 29, 2017

Flashing LED Advertising Badge #1   -  I have seen numerous flashing light badges at trade shows and conventions.  They are often handed out as gifts to promote some business.  The devices often use inefficient circuits, which cause the battery power source to be quickly depleted . . . Hobby Circuit designed by David Johnson P.E.-March 26, 2002

Flashing Light to simulate Car Alarm   -  Whenever the car’s ignition is turned off, this circuit activates a flashing LED, which can be positioned to appear as an active alarm system . . . Hobby Circuit designed by David Johnson P.E.-July 09, 2006

Flexible Outputs from Square Wave Driver   -  This circuit can produce an output signal ranging from DC to 100KHz.  It can source a voltage ranging from 1v to 30v.  It can sink a voltage ranging from zero volts to –30v.  It can drive up to 200ma of current and can even be switched to a floating tristate . . . Hobby Circuit designed by Dave Johnson P.E.-July 08, 2000

Fluorescent Lamp Intensity Modulator   -  This hobby circuit was designed to experiment with using small fluorescent lamps as a broad pattern source of modulated light.  This hobby circuit hits the small lamp with narrow 1us pulses at a rate of 10KHz.  Each pulse launches about 10 watts of visible light.  The lamp starting method is a bit crude but the circuit does work.   . . . Hobby Circuit designed by David A. Johnson P.E.-June 27, 2000

Fluorescent Lamp Night Light Needs Only 1 Watt   -  if you are tired of replacing small night light lamps, try this circuit.  The line powered circuit uses a long life cold cathode fluorescent lamp.  A simple charge pump technique runs the lamp without any transformer . . . Hobby Circuit designed by David Johnson P.E.-March 26, 1999

Footstep Alarm for Human Traffic   -  This circuit processes the amplified signals from the footstep detector circuit and activates a microprocessor when the circuit detects footsteps.  At has an adjustable sensitivity . . . Hobby Circuit designed by David Johnson P.E.-July 11, 2006

Form Push-Pull Driver using N-Ch & P-Ch Transistors    -  This circuit can produce high speed output signals with fast rise and full times.  The unique change pump action allows the voltage of the upper P-ch device to range from millivolts to hundreds of volts.  The output current is only limited by the rating of . . . Hobby Circuit designed by David A. Johnson P.E.-June 27, 2000

Front Desk Service Beeper   -  This device functions like a lobby desk service request bell.  A short beep is sounded whenever the large pushbutton on top of the device is pressed.  Once pressed, the device will not make another beep until at least 2 minutes of time has elapsed . . . Hobby Circuit designed by Dave Johnson P.E.-September 25, 2005

Front End + Power Supply Circuits of the Electric Filed Disturbance Monitor   -  This schematic is the power supply and front-end sections of my field monitor, "Electric Field Disturbance Monitor".  The system can detect human and animal motion by the electric fields they disturb . . . Hobby Circuit designed by David A. Johnson P.E.-March 26, 2002

Front-End Circuit-Modulated Light Receiver   -  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

Fully Isolated 50/60hz Sync Generator   -  This circuit will produce a single pulse at the zero voltage cross points of the power line voltage.  An opto-coupler provides a very safe 5KV isolation . . . Hobby Circuit designed by David A. Johnson P.E.-December 12, 2004


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


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