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Circuits designed by David Johnson, P.E.
Last Updated on: Thursday, December 07, 2017 02:06 PM


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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


Machine Power Loss Beeper  -  For some medical equipment it is important for an operator when power is lost to the machine.  The beeper is powered from a 9v battery and requires the machine to have a power switch with a third set of contacts . . . Circuit by David A. Johnson P.E.-March 26, 1999

Machine Vibration Triggers Hour Meter  -  This 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.  Machine vibrations are detected by an off-the-shelf piezo . . . Circuit by David A. Johnson P.E.-December 26, 1998

Make a Geophone to Detect 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.   . . . Circuit by Dave Johnson P.E.-June 02, 2006

Medical Fluid Detector  -  A simple 40KHz 12v peak to peak square wave signal generator, using a 555 timer oscillator, was fed to the metal needle and the whole vertical indexing system, which was electrically isolated from everything else.  On the receiver end, a copper foil electrode, which was designed to fit snugly on the bottom of a plastic cup, acted as a holder for the fluid container. . . . Dave Johnson, Lubbock TX-DC Magazine - Issue 11 July 2010

Medium Power 125khz Oscillator  -  This circuit adds even more inverters in parallel to deliver yet more power.  The values shown are for 125KHz . . . Circuit by Dave Johnson P.E.-March 12, 2002

Medium Power 125khz Oscillator #2  -  This circuit is similar to MEDiUM POWER 125KHZ OSCiLLATOR but adds even more inverters in parallel to deliver yet more power.  The values shown are for 125KHz.   . . . Circuit by David A. Johnson P.E.-March 12, 2002

Medium Power 40Khz Ultrasound Transducer Driver  -  This crystal controlled circuit drives a 40KHz piezo transducer with a 30v peak to peak signal . . . Circuit by Dave Johnson P.E.-July 09, 2006

Micro Power 40Khz Burst Laser Diode Driver  -  Some laser tag or simulated combat games can use this circuit to send short bursts of modulated laser light at the opponent's vest, equipped with a matching light receiver.  The circuit operates from three 1.5v cells (4.  5v) that should provide enough energy . . . Circuit by Dave Johnson P.E.-June 04, 2000

Micro Power Over-Temperature 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 . . . Circuit by Dave Johnson P.E.-June 04, 2000

Micropower CMOS Oscillator, Draws Only 0.5ua  -  if truly low power oscillators interest you, this circuit draws a mere 2 microwatts (500nA) from a 6v battery.  It uses a very inexpensive C-MOS IC to produce a frequency of 2Hz.  However, by changing the component values you can push it to 300Hz . . . Circuit by David A. Johnson P.E.-June 03, 2000

Micropower Pulse Generator  -  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 . . . Circuit by David Johnson P.E.-June 03, 2000

Minature 24VAC Isolated +5V Supply  -  24vac is a very popular power supply in many industrial systems.    it is often used in systems that involve water.    it is also popular with many inside and outside lighting systems.    The lower voltage means the danger of human electrocution is much less.     . . . Circuit by David Johnson P.E.-July 29, 2009

Miniature 5v Line Powered Isolated Supply  -  Often a circuit requires a 5v DC supply to power some logic circuits.  The conventional method is to use an AC wall adapter.  But, many systems, which bring AC power onto a circuit board, need a small AC to DC power supply right on the circuit board.  The . . . Circuit by David Johnson P.E.-July 15, 2009

Miniature AC to DC Power Supply  -  Electronic systems are getting quite efficient these days.  I seldom design a small product that requires more than 100 milliwatts of power.  Often, if the product is not going to be powered by batteries, it requires a wall mounted AC to DC power adapter or a small on-board power module.   . . . Dave Johnson, Lubbock TX-DC Magazine - Issue 15 Jan 2011

Miniature Isolated 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.  The voltage spikes produce . . . Circuit by David A. Johnson P.E.-June 09, 2000

Miniature Lighthouse Light Simulator  -  The circuit I came up with is shown below.  It uses two dual low power op amps.  The first two devices form a classic oscillator circuit whose output is a triangle waveform signal.  That signal is routed to a current regulator circuit, which converts the triangle voltage signal to a triangle current signal through the lighthouse LED.  A third op amp generates pulses timed so they occur at the peak of the triangle waveform.  The result is a LED, which gradually grows brighter, then flashes even brighter before dimming again.  This should produce a light, which simulates a rotating lighthouse light . . . Circuit Solution by Dave Johnson P.E.-May 07, 2006

Mm5437 Noise Generator  -  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. . . . Circuit by David Johnson P.E.-July 30, 2017

Modified 4 D Cell LED Lantern  -  While shopping at a sporting goods store one day, I spotted a compact LED lantern.  It looked like the kind of lantern I could modify. The lantern LEDs were grouped into three sections of 7 LEDs each, oriented into 120 degree angles.  The LEDs were standard T 1-3/4 epoxy types.  The lantern had a three mode switch which selected between off, full power and half power modes.  At the half power mode, only half of the 21 LEDs were illuminated.  At full power all LEDs were illuminated. . . . Circuit by David Johnson P.E.-September 21, 2017

Modified Cheap Solar LED Path Light  -  Modification of a typical solar path light with a standard 1000ma-hour NiMH AAA cell.  I then replaced the small 4 cell solar panel with a larger 4 cell unit, which produced 150ma in the sun.  Next, I simply changed the 470uH coil on the circuit board to a 22uH coil.  The lower inductance increased the battery current to 40ma when the LED light was on, which translated to about 13ma LED current.  The light was much brighter . . . Circuit by David Johnson P.E.-May 02, 2014

Modified Colman Lantern3  -  While shopping at a sporting goods store one day, I spotted a compact LED lantern.  It looked like the kind of lantern I could modify. The lantern LEDs were grouped into three sections of 7 LEDs each, oriented into 120 degree angles.  The LEDs were standard T 1-3/4 epoxy types.  The lantern had a three mode switch which selected between off, full power and half power modes.  At the half power mode, only half of the 21 LEDs were illuminated.  At full power all LEDs were illuminated. . . . Circuit by David Johnson P.E.-September 21, 2017

Modulated Light Monitor #1  -  This battery powered circuit will work from DC to 500KHz.  It is designed to connect to an oscilloscope to monitor the light level changes and modulated signals . . . Circuit by David Johnson P.E.-July 09, 2006

Modulated light receiver circuit  -  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 . . . Circuit by David A. Johnson P.E.-June 04, 2000

Momentary Operation Touch Switch  -  This simple circuit uses a single IC to form a nice touch switch circuit.    A single transistor forms the remote active switch sensor.    Multiple switches can be wired in parallel.    The switch circuit can be located about 500 feet from the control circuit . . . Circuit by Dave Johnson P.E.-March 12, 2002

Monitor Clear Fluids  -  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 . . . Circuit by David A. Johnson P.E.-July 11, 2006

Monitors Pump Motor  -  This circuit solves this problem in a novel way.  It clips on the outside of the pump motor’s power cable and provides a transistor switch closure whenever the circuit detects current flowing to the motor.  The circuit draws so little current that a small lithium cell will power the circuit for years . . . Circuit Solution by David A. Johnson P.E.-November 18, 2004

Motion Alarm using piezo Device  -  An inexpensive piezoelectric device is used as a motion sensing device for this motion alarm . . . Circuit by David Johnson P.E.-July 09, 2006

N-Ch & P-Ch Transistor Form Push-Pull Driver  -  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 . . . Circuit by David A. Johnson P.E.-June 27, 2000

Night Light from White LED  -  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 . . . Circuit by David Johnson P.E.-November 06, 2008

Nine-Volt Battery Eliminator  -  if you use 9v battery powered devices for long periods of time, you may get tired of constantly changing batteries.  The circuit below can be wired into any 9v battery powered device, drawing power from an external AC to DC power adapter.  I designed the circuit . . . Circuit by David A. Johnson P.E.-December 07, 2009

Nine-Volt Battery Voltage Monitor  -  This circuit turns on a LED whenever the voltage of a standard 9v battery connected to the circuit drops below 7.  2 volts.  It uses a LTC1440 comparator, which also contains a 1.  18v reference diode.  In standby mode, the circuit draws only 4uA . . . Circuit by Dave Johnson P.E.-July 09, 2006

Non-Isolated Off-Line AC to DC Power Supply  -  The design below does indeed fit within a one square inch circuit board area.  It can be used over a wide 24vac – 120vac input voltage.  The circuit gates only small slivers of the rectified AC signal to a 470uF energy storage capacitor.  The 180K and the 10K resistors define the peak voltage fed to the capacitor.  Other resistor values can be used to shift the DC output voltage up or down.  Remember, this circuit should only be used with DC circuits that can be connected directly to the power line.  Dangerous voltages exist everywhere.   . . . Circuit Solution by Dave Johnson P.E.-July 13, 2006

Non-Isolated Off-Line AC to DC Power Supply  -  This compact efficient circuit can provide up to 100ma of a regulated 5 volts from an AC power source ranging from 20vac to 120vac . . . Circuit by David Johnson P.E.-July 13, 2006

Off-Line Miniature Isolated 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.  The voltage spikes produce . . . Circuit by David A. Johnson P.E.-June 09, 2000

On/Off Flip/Flop Circuit with Automatic Timeout  -  This circuit is ideal when a device needs to be turned on and off with a single pushbutton switch, but also needs to turn itself off after some period of time.  With the components shown, the output will stay on for only about 20 seconds . . . Circuit by Dave Johnson P.E.-December 16, 2004

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.   . . . Circuit by Dave Johnson P.E.-November 22, 2009

On/Off Latch Circuit with 2 Second Delay  -  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 . . . Circuit by Dave Johnson P.E.-July 02, 2013

On/off Pushbutton Switch with 30 Minute Timeout  -  I received an email from a Discover Circuits visitor.  He wanted to control power to a LED camping light he was building.  He wanted to turn the light on and off with a small pushbutton switch.  He also wanted a timer so the light would not stay on longer than 30 minutes at a time.  It seems that his kids often turned lights on when going to bed and then forgot to turn them off . . . Circuit by David Johnson P.E.-January 08, 2012

On/Off Switch with Latching Relay  -  The circuit below switches AC or DC power to a load using an ultra low power 3v latching relay with two coils.  The relay can handle about 10 amps of current, up to 250vac.  Each time the small pushbutton is pressed, the circuit either latches the relay . . . Circuit by Dave Johnson P.E.-December 20, 2009

One Shot (D-Flip/Flop) Circuit  -  Yes you can use cheap D flip/flop logic circuits as nice one-shot pulse generators.  This schematic shows how the popular CD4013 and the CD74HC74 can be used to generate pulses ranging from nanoseconds to seconds . . . Circuit by David A. Johnson P.E.-March 26, 2002

One-Line Telephone Line Status Indicator  -  This circuit monitors one phone line . . . Circuit by David A. Johnson P.E.-June 10, 2000

Optical Fiber Indicator  -  The concept was to have four germanium photodiodes along the front of a suitable plastic box. Each photodiode would have a narrow band optical filter placed in front so it would respond only to light in that specific narrow wavelength. A comparator circuit would monitor the light from each photodiode . . . Dave Johnson, Lubbock TX-DC Magazine - Issue 1 Sept 2009

Optical Fiber Pressure & Motion Test  -  The circuit uses an off-the-shelf bright red LED light source, designed for plastic optical fibers.  It also uses a matching phototransistor light detector.  The devices are designed for plastic fiber.  I would suggest you keep the total fiber length less than 50 feet.  Bending or stepping on the fiber will produce a detectable output signal. . . . Dave Johnson, Lubbock TX-DC Magazine - Issue 15 Jan 2011

Optical Interrupter Draws Microamps  -  This circuit is great for battery-powered systems that use slotted type optical interrupters.  It draws only 10uA from a 3v battery that should allow up to 5 years of operation from a lithium battery . . . Circuit by David A. Johnson P.E.-June 04, 2000

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


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