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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


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

Parallel LC Oscillator with CMOS Inverter    -  I have used this parallel resonant LC oscillator circuit countless times.  The oscillator frequency is determined by the inductor and capacitor values.  I have shown an adjustable inductor to make it easy to set the frequency to a specific value . . . Hobby Circuit designed by Dave Johnson P.E.-March 12, 2002

Peak to Peak 300v Signal Generator   -  This circuit converts a square wave signal to a +-150 volt output signal with fast 100nS rise and fall times . . . Hobby Circuit designed by Dave Johnson P.E.-June 03, 2000

Photovoltaic Solar Panels-Ideal Blocking Diode Circuit   -  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 David Johnson P.E.-January 26, 2009

Piezoelectric Device used for Motion Alarm   -  An inexpensive piezo wafer is used to detect vibration and when the vibration is sufficient a switch is activated . . . Hobby Circuit designed by David Johnson P.E.-July 09, 2006

Piezoelectric Water Flowing Indicator   -  The vibrations associated with water flowing through a pipe are picked up by an inexpensive piezo wafer.  The signal from the wafer is first boosted by a micropower transistor amplifier and then fed to an ultra low power voltage comparator . . . Hobby Circuit designed by David Johnson P.E.-July 26, 2009

Plus & Minus DC Power Supply   -  This is a classic example of a regulated DC power supply that produces both a positive 15v and a negative 15v from a 20vac wall adapter . . . Hobby Circuit designed by David A. Johnson P.E.-December 13, 2004

Poor Man's Timer   -  Often during testing of certain equipment and components, you would like to keep track of the elapsed time in hours, minutes and seconds.  There are some nice commercial digital timers and counters available for just this sort of application.  However,  . . . Hobby Circuit designed by Dave Johnson P.E.-August 24, 2008

Power Supply for Digital Panel Meters that is Isolated   -  Many inexpensive digital panel meters, such as the one shown below, are designed to operate from a 9v battery.  However, the nature of the panel meter internal design often requires that the DC supply used to power the device be isolated from the ground . . . Hobby Circuit designed by Dave Johnson P.E.-September 13, 2008

Precision Low Capacitance Meter   -  This circuit was originally designed to measure the volume of fluid inside a medical syringe.  As designed, it produces a zero to 5 volt output, corresponding to a capacitance change of about 10 picofarads . . . Hobby Circuit designed by David A. Johnson P.E.-December 12, 2004

Press & Hold Latching Circuit   -  A Discover Circuits visitor needed a latch circuit which could operate using a power supply voltage ranging from 3v to 24v.  He wanted to use a tiny pushbutton switch to turn on and off power to a load.  However, he wanted a 2 second delay between the switch activation and the state change of the output . . . Hobby Circuit designed by David Johnson P.E.-July 02, 2013

Produces Beep once each Minute   -  This circuit produces a short beep once each minute.  It is powered directly off the 120vac power line to remind you that a device connected to the circuit is turned on.  It is simple enough to be packaged inside a small plastic box . . . Hobby Circuit designed by David Johnson P.E.-June 03, 2000

Protects from Battery Polarity Reversal   -  This simple circuit can protect a sensitive electronic circuit from an accidental connection of a battery with a reversed polarity.  The N-channel FET connects the electronic device to the battery only when the polarity is correct.  The circuit shown was . . . Hobby Circuit designed by David Johnson P.E.-March 09, 2002

Pulse Generator uses Micropower   -  it is hard to design a pulse generator that produces clean logic pulses while drawing very low current.  This circuit is designed to produce short 2mS pulses at a rate of one per second while drawing only 1 microamp from a 9 volt battery . . . Hobby Circuit designed by David A. Johnson P.E.-June 03, 2000

Pushbutton On-Off Latch Circuit   -  Often you want to turn on and off power to a device with a single pushbutton switch.  The circuit below performs this logic function with just a few parts and can operate from DC supplies between +3v to about 15v.  It uses two inverters within a 74C14 or a CD4069 hex inverter package.  Each press of the button toggles between the two on/off logic states.   . . . Hobby Circuit designed by David Johnson P.E.-January 09, 2010

Pushbutton Switch Through Glass    -  This simple technique allows a mechanical pushbutton switch assembly to activate a reed type relay through a pane of thick glass.  Pushing the button moves a magnet near the reed relay, closing the relay contacts . . . Hobby Circuit designed by Dave Johnson P.E.-February 10, 2002

PV Solar Cell Test Fixture   -  This is an illustration of a test fixture, which can be used to test individual solar cells for short circuit current.  Using a PIN photo diode and a control circuit, the solar cells can be tested under constant light level conditions . . . Hobby Circuit designed by David Johnson P.E.-July 09, 2006

PV Solar Panels-Ideal Blocking Diode Circuit   -  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 Johnson P.E.-January 26, 2009

PWM Circuit for Motor Speed Control   -  Sometimes you want to slow down a brush type DC motor.  The most efficient way to do this is with a pulse width modulation (PWM) technique.  The hobby circuit below can operate from about 3 volts to 15 volts.  The frequency is fixed at about 2KHz but the pulse . . . Hobby Circuit designed by David A. Johnson P.E.-December 16, 2007

PWM Motor Controller uses a 555 Timer   -  Using a CMOS version of the 555 timer, this circuit can be used to control the speed of a motor by adjusting the duty cycle of the pulses sent to the motor . . . Hobby Circuit designed by David Johnson P.E.-June 30, 2006

Quartz_Clock_Solar_Powered   -  Connect a solar panel to a quality AA size 1One of my homes in Colorado had a large battery powered quartz clock above the fireplace.  It was powered by an AA size 1.5v alkaline cell.  The battery would run the clock for about a year or so, then I would have to break out a tall step ladder and replace the battery for another year or so of operation. That gave me a great 10:1 energy margin. . . . Hobby Circuit by David Johnson P.E.-September 21, 2017

Radio Tower Lamp Monitor   -  The circuit below uses two 3 amp diodes to produce a fairly constant 2 volts whenever current is routed to the tower lamp.  The voltage is used to power a bright LED.  The LED will only turn on when current is actually flowing to the lamp.  With the component values shown, the circuit will work with lamps ranging from 40 to 250 watts.   . . . Hobby Circuit designed by David Johnson P.E.-January 00, 1900

Ramping Lamp Driver   -  This circuit drives any 12v lamp, incandescent or LED type, in a ramping fashion.  Each press of the button toggles the lamp from a fully off mode to a fully on mode.  But, instead of an instantaneous lamp intensity change, the power is slowly ramped up a . . . Hobby Circuit designed by Dave Johnson P.E.-December 21, 2007

Really Loud Output Beeper Circuit   -  I you need a real loud beeper, this circuit delivers about 110db (12 inches away) from a 9v battery using a single inexpensive C-MOS IC .  An off-the-shelf piezoelectric beeping device is driven at resonance to insure maximum efficiency.  By changing the control IC to a 74AC14, the same circuit can operate from 3v and 1.5v batteries . . . Hobby Circuit designed by Dave Johnson P.E.-June 03, 2000

Rectifier-Fullwave   -  I have used this handy circuit many times.  It accurately converts an AC signal into pulsing DC, which can be filtered to provide an average of the input voltage.  It works from millivolts to volts.  The circuit shown requires a stable +5v reference if a . . . Hobby Circuit designed by David Johnson P.E.-February 12, 2002

Reduced Power Sequential LED Flasher   -  The 74HC4017 is a neat decade counter which has 10 decoded outputs.  When supplied with a low frequency clock and with a LED attached to each of the outputs, an interesting ten step sequential flasher effect can be produced.  The LEDs can be configured in . . . Hobby Circuit designed by David A. Johnson P.E.-November 30, 2008

Reflected Infrared Light Switch   -  infrared light reflected off a finger is used to activate this switch circuit.  Drawing only 30uA from a 3v supply, this circuit will detect a human finger with a range of about 1 inch.  The sensor uses an inexpensive infrared LED and a matching photo diode . . . Hobby Circuit designed by Dave Johnson P.E.-July 09, 2006

Relay Driver with Reduced Power   -  Relays can handle a lot of power.  However, for certain power sensitive designs you would like to reduce the power needed to hold a relay closed.  The circuit below performs such a task.  It uses a single CD4093 quad NAND gate.  When the “on” logic input . . . Hobby Circuit designed by David A. Johnson P.E.-August 03, 2008

Remote Range Extender TV/VCR   -  I often get frustrated by how poor some infrared remotes in many new electronic devices operate.  I used to be able to turn on the TV from 30 feet away.  Now, it seems that I have to get within 15 feet.  To address this DC Magazine - Issue, I designed the circuit shown below.  The circuit taps into the TV remote’s existing infrared LED and drives 8 more efficient devices.  The result is a communications range some 4 to 5 times longer.   . . . Hobby Circuit designed by David Johnson P.E.-December 14, 2009

Remote TV Camera Power   -  A while back I received an email from a company with a problem.  They needed a security camera installed at some remote location.  The camera was a high quality color camera sending out standard NTSC video through a long 500 foot 50 ohm coax cable.  With some difficulty they got the coax strung.  They were told that there would be AC power near the camera location to power that device.  But, they then learned that in fact, there was no power available.  They thought about using a solar panel and a battery but they decided to call me for help instead.  Was there some way to power the camera without stringing another cable? . . . Hobby Circuit designed by David Johnson P.E.-July 03, 2011

Replace a Pushbutton Switch with this Infrared Safety Switch   -  Using a slotted optical sensor, this circuit can be used as a replacement for a large mushroom pushbutton safety switch . . . Hobby Circuit designed by Dave Johnson P.E.-July 11, 2006

Revisited-Model Train Lighthouse Flasher   -  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.-July 11, 2006

RF 2.45Ghz Signal Detector   -  This passive RF indicator is made from a few simple parts.  A 100uA moving coil meter is used to display the relative intensity of the RF signal.  This circuit can be used with some cell phones and many cordless telephones . . . Hobby Circuit designed by Dave Johnson P.E.-July 09, 2006

RF Signal Detector 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

RFID Smart Key Detector   -  The hobby circuit below was designed to indicate if a key held over the small coil of wire contains a 125KHz RFID chip.  These chips are often used in smart car ignition keys.  The left side circuit forms a 125KHz power oscillator, which drives the 680uH a . . . Hobby Circuit designed by Dave Johnson P.E.-July 09, 2006

RFID Test Circuit   -  I designed this test the concept of using light techniques to send identification data instead of RF.  . . . Hobby Circuit designed by David Johnson P.E.-July 08, 2000

RS-232 Serial Interface Status Indicator Circuit   -  I designed this circuit many years ago and have used it several times since.  It uses a single logic IC to indicate the TXD and RXD line activity of a typical RS-232 serial data communications link.  The thresholds are set at plus 3 volts and minus 3 volts.  Two dual color LEDs are used as indicator lights . . . Hobby Circuit designed by David A. Johnson P.E.-December 15, 2004


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


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