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Circuits designed by David Johnson, P.E.
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David Johnson's Circuits
Circuits + Descriptions

from Dave's Circuits & Circuit Solutions


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


Garage Door Closer  -  The circuit below is designed to automatically close a garage door, if it was left open for a long period of time.  A reed relay and magnet combination sense when the door is fully open.  An ultra low power voltage comparator oscillator and two 74HC4040 ICs  are used to generate the time delay . . . Dave Johnson, Lubbock TX (May 14, 2011)-DC Magazine - Issue 18 May 2011

Hand Wave Motion Detector  -  The circuit below works quite well in typical indoor room lighting.  I would not recommend its use in direct sunlight.  Two small PIN photodiodes positioned about one inch apart form a shadow detector.  With no shadow cast on the devices, both devices produce nearly identical current levels . . . Circuit Solution by Dave Johnson P.E.-August 21, 2005

Hidden Panic Switch  -  Design an electronic switch which would be positioned behind a wall at several key positions and would be activated when an adult human hand was pressed against the wall at that position.  The best way to detect the human hand against a wall was with a capacitance switch.  The QTFS3X from Faraday switches looked like a perfect match.  The switch could be powered by a DC voltage down to 3v.  It required only 30ua of current.  It was quite small and would easily fit behind the wall. . . . Dave Johnson, Lubbock TX-DC Magazine - Issue 18 May 2011

High Intensity Line Powered LED Flasher  -  There are times when you would like to generate an intensely bright flash of light using electrical power from the AC line.  The circuit below can drive a one to three watt power LED with about 350ma of peak current.  Since the circuit drives the LED with . . . Circuit by David Johnson P.E.-December 07, 2008

High Pass Active Filters  -  This is a collection of inverting and non-inverting active high pass filter circuits.  I included one, two three, four and six pole filter circuits.  You can change the component value ratios shown to achieve any frequency cut-off you may need . . . Circuit by Dave Johnson P.E.-February 11, 2002

High Power Flashing LED  -  The circuit converts an off-the-shelf solar powered LED path light from producing a steady state light to one that produces a flash. This circuit includes a tiny dual Schmitt trigger inverter IC which form the pulse generator and the daylight sensor circuit . . . Dave Johnson, Lubbock TX-DC Magazine - Issue 7 Mar 2010

High Power 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 . . . Dave Johnson, Lubbock TX (Aug 10, 2008)-DC Magazine - Issue 7 Mar 2010

High Power Touch Switch Exciter Circuit  -  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 . . . Circuit by David A. Johnson P.E.-February 11, 2002

High Sound Output Beeper  -  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 . . . Circuit by Dave Johnson P.E.-June 03, 2000

High-speed 75MHz light receiver  -  This circuit uses one tiny C-MOS inverter IC to form a modulated light receiver with a very fast response.  It is designed around a PIN photo diode that is packaged for use with plastic optical fibers.  It can be used as an optical fiber receiver.  By using the open end of the optical fiber it can "sniff" out any modulated light signals . . . Circuit by David Johnson P.E.-June 11, 2000

Honeybee Counter  -  I designed a circuit similar to this one a long time ago to help a beekeeper count the number of bees going into or out of a hive.  The low power circuit uses a slotted opto-sensor to detect the passing bees.  The circuit advances an electronic counting . . . Circuit by David A. Johnson P.E.-July 08, 2000

Human Footstep Alarm  -  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 . . . Circuit by David A. Johnson P.E.-July 11, 2006

Human Traffic Footstep Detector Preamp  -  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 . . . Circuit by David A. Johnson P.E.-July 11, 2006

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

Illuminated Banister  -  The remote capacitance sensor circuit is placed inside a small potting shell, which contained a three screw terminal block and a single turn variable resistor.  The variable resistor allowed the capacitance needed to activate the switch to be set from about 10pf to 170pF.
 . . . Dave Johnson, Lubbock TX-DC Magazines - 2nd Q 2012

Improved Solar LED Spot Light  -  Nearly all the Chinese made solar powered LED lights I see being sold at Lowe's and Home Depot home improvement centers are poorly designed.  Their solar panels and battery packs are all undersized.  The light from their Chinese made LEDs fade rapidly and the devices never make it through a complete night before the light dies . . . Circuit by David Johnson P.E.-February 03, 2013

Incandescent Lamp Inrush Current Limiter  -  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 . . . Circuit by David A. Johnson P.E.-July 09, 2006

Indicates when it is Time to Dust  -  I have used the circuit below for many different applications, which require ultra low power drain.  It uses a single CA4013 flip/flop.  One section forms a pulse generator.  The generator produces 100uS pulses at a rate of about 1 per second . . . Circuit Solution by Dave Johnson P.E.-July 06, 2000

Indicates when it is Time to Dust  -  I have used the circuit below for many different applications, which require ultra low power drain.  It uses a single CA4013 flip/flop.  One section forms a pulse generator.  The generator produces 100uS pulses at a rate of about 1 per second . . . Circuit Solution by David A. Johnson P.E.-July 06, 2000

Indicates when it is Time to Dust  -  I have used the circuit below for many different applications, which require ultra low power drain.  It uses a single CA4013 flip/flop.  One section forms a pulse generator.  The generator produces 100uS pulses at a rate of about 1 per second . . . Circuit Solution by Dave Johnson P.E.-July 06, 2000

Indicates when it is Time to Dust  -  I have used the circuit below for many different applications, which require ultra low power drain.  It uses a single CA4013 flip/flop.  One section forms a pulse generator.  The generator produces 100uS pulses at a rate of about 1 per second . . . Circuit Solution by David Johnson P.E.-July 06, 2000

Indicates when it is Time to Dust  -  I have used the circuit below for many different applications, which require ultra low power drain.  It uses a single CA4013 flip/flop.  One section forms a pulse generator.  The generator produces 100uS pulses at a rate of about 1 per second . . . Circuit Solution by David Johnson P.E.-July 06, 2000

Indicates when it is Time to Dust  -  I have used the circuit below for many different applications, which require ultra low power drain.  It uses a single CA4013 flip/flop.  One section forms a pulse generator.  The generator produces 100uS pulses at a rate of about 1 per second . . . Circuit Solution by David Johnson P.E.-July 06, 2000

Indicates when it is Time to Dust  -  I have used the circuit below for many different applications, which require ultra low power drain.  It uses a single CA4013 flip/flop.  One section forms a pulse generator.  The generator produces 100uS pulses at a rate of about 1 per second . . . Circuit Solution by Dave Johnson P.E.-July 06, 2000

Indicates when it is Time to Dust  -  I have used the circuit below for many different applications, which require ultra low power drain.  It uses a single CA4013 flip/flop.  One section forms a pulse generator.  The generator produces 100uS pulses at a rate of about 1 per second . . . Circuit Solution by David Johnson P.E.-July 06, 2000

Indicates when it is Time to Dust  -  I have used the circuit below for many different applications, which require ultra low power drain.  It uses a single CA4013 flip/flop.  One section forms a pulse generator.  The generator produces 100uS pulses at a rate of about 1 per second . . . Circuit Solution by David Johnson P.E.-July 06, 2000

Inductor Self-Resonance Tester  -  if you want to know what the self-resonance frequency is of an inductor, this circuit will help.  It adds only a few picofarads of parallel capacitance to the inductor under test.  With the aid of an oscilloscope and a signal generator this circuit will allow you to measure resonant frequencies from kilohertz to over 10 megahertz . . . Circuit by David Johnson P.E.-June 09, 2000

Infrared Reflected Light Switch  -  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 . . . Circuit by David A. Johnson P.E.-July 09, 2006

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

Infrared 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.   . . . Circuit by Dave Johnson P.E.-October 05, 2005

IR Remote LED Indicator Light  -  There are times when you would like to transmit a signal from one LED indicator light to second LED at another location.  The circuit below works well for this application.  It takes advantage of the fact that the internal infrared LED inside an opto-isolator . . . Circuit by Dave Johnson P.E.-December 26, 2008

Is it Time to Dust?  -  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 . . . Circuit by Dave Johnson P.E.-July 06, 2000

Isolated AC Current Monitor  -  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 . . . Circuit by David A. Johnson P.E.-July 10, 2006

Isolated AC Voltage Spans 0VAC to 280Vac  -  I designed and built this circuit about 25 years ago.  It came in handy for many projects that were powered from 120 VAC, 240 VAC and 277 VAC.  It provides complete isolation from the power line.  It uses two 1:1 isolation transformers that are wired in parallel . . . Circuit by David Johnson P.E.-July 08, 2000

Isolated Power Supply for Digital Panel Meters  -  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 . . . Circuit by David A. Johnson P.E.-September 13, 2008

Isolated Remote Switch Circuit  -  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 . . . Circuit by Dave Johnson P.E.-January 04, 2009

Isolation Transformer Circuits  -  A while back I needed to test a circuit at 240vac.  Since I needed to safely test the circuit using my oscilloscope, I needed the 240vac to be fully isolated from the power line.  So, to step up the voltage, I bought a small isolation transformer from Digikey . . . Circuit by David Johnson P.E.-May 29, 2011

JFET High Impedance 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 . . . Circuit by Dave Johnson P.E.-July 11, 2006


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