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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


Laptop Power Supply   -  Concept Only.  I have a big screen HP laptop computer.  The large brick size AC to DC power supply is rated at 19.  2v and 9.  5 amps, which is about 180 watts.  I’d like to be able to use the thing in my car.  I looked into a 12v car adapter for it but never really found one that I liked.   . . . Hobby Circuit designed by Dave Johnson P.E.-July 26, 2009

Laser Burst Light Detector   -  This circuit was originally designed to detect weak flashed of laser light bounced off of a fabric video projection screen.  It was used as part of a firearm training system.  It generates a 100mS output pulse whenever it detects a 3ms to 5ms laser burst, modulated at 40KHz.  It is very sensitive and could be modified for long range laser communications.   . . . Hobby Circuit designed by David Johnson P.E.-June 13, 2000

Laser Light Detyector-10Mhz to 20Mhz   -  This circuit was originally designed to detect laser light pulses for an optical Ethernet communications system.  It has good ambient light immunity . . . Hobby Circuit designed by Dave Johnson P.E.-June 14, 2000

Latching_Relay_Dusk_To_Dawn   -  Over the years I have had to replace many dusk to dawn switches for outside lights.  These switches turn on a light during the night, then switch them off during daylight hours.  Some commercial switches are not sensitive enough to detect when the sun is out.  Others flutter badly during the dawn and dusk switching transitions, burning out compact fluorescent lamps, which do not like rapid power fluctuations. . . . Hobby Circuit by David Johnson P.E.-July 31, 2017

LC Oscillator Medium Power 125Khz   -  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 . . . Hobby Circuit designed by David A. Johnson P.E.-March 12, 2002

LED Array powered by 24 VAC   -  24vac is a popular voltage.  It is often used in low voltage lighting systems and industrial controls.  It is much less dangerous than 120vac/240vac line voltages.  This hobby circuit below is one method to efficiently power a cluster of 7 white LEDs from 24vac.   . . . Hobby Circuit designed by David A. Johnson P.E.-December 19, 2009

LED Camping Lantern with Dimmer   -  A while back I received an email from a Discover Circuits visitor who wanted to build his own LED camping lantern.  He wanted to use a single bright LED powered by 3 large alkaline D cells.  He also wanted to be able to dim the light intensity down to a low night light level, to extend the battery life.  The circuit below performs this task . . . Hobby Circuit designed by Dave Johnson P.E.-December 08, 2013

LED Driver-Wireless   -  The circuit solves this problem by sending power to the LED through the plastic, using a magnetic coupling technique.  The circuit below can route power through plastic enclosures as thick as ¼ inch.  The circuit will not work through metal boxes . . . Hobby Circuit designed by David A. Johnson P.E.-November 02, 2008

LED Flasher needs only 1.5 VOLTS   -  To squeeze even more energy from a alkaline battery cell, this circuit adds two transistors to a circuit similar to the above design to boost the efficiency.  A small 1.5 volt alkaline N cell should flash the LED for a full year.  It too uses a "charge pump" technique to provide a LED the needed voltage . . . Hobby Circuit designed by David A. Johnson P.E.-June 03, 2000

LED Flasher that is Battery Free   -  LED flashers have been used for a wide variety of applications.  Some flasher units have been used in food and hardware stores, to draw attention to sale items and are often attached to boxes which dispense product discount coupons . . . Hobby Circuit designed by Dave Johnson P.E.-December 11, 2010



LED Flasher Universal 3v   -  The electronic circuit below will flash any LED color with fixed current pulses powered by a 3v battery.  It uses a charge pump approach, which routes a constant current pulse through the LED, regardless of the LED voltage requirement.  Using this approach . . . Hobby Circuit designed by Dave Johnson P.E.-June 22, 2008

LED Flasher-Wig/Wag   -  This simple circuit will flash two LEDs in an alternating fashion . . . Hobby Circuit designed by Dave Johnson P.E.-December 18, 2004

LED Flasher-Wireless Circuit   -  When you would like to flash a LED through a thick plastic case without wires, use this hobby circuit.  It performs this feat.  It draws about 300ua of average current at 5v.  It can be powered from a supply ranging from 3v to 6v . . . Hobby Circuit designed by David A. Johnson P.E.-January 09, 2011

LED 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 Dave Johnson P.E.-July 11, 2006

LED Lighthouse Flasher for HO Model Train    -  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 Dave Johnson P.E.-July 11, 2006

LED Strings powered by AC Line   -  This shows 4 different ways to string white LEDs that are powered by a 120vac or 240vac power line. __ Designed by Ken Schultz, drawn Dave Johnson 12.18.2004-December 18, 2004

LED Test Signal Generator-40Khz   -  This 40KHz crystal controlled oscillator circuit drives an infrared LED with powerful 40ma pulses.  The circuit can be used to test optical communications circuits, designed to receive 40KHz modulated light signals . . . Hobby Circuit designed by Dave Johnson P.E.-February 14, 2002

LED/Laser Light Output Intensity Meter   -  This circuit uses a large 1cm X 1cm silicon PIN photo diode and a transimpedance amplifier to measure the light power output of infrared and visible LEDs and laser diodes.  It can be modified to produce almost any milliwatts to volts scale factor.  It can b . . . Hobby Circuit designed by Dave Johnson P.E.-July 08, 2000

LED_Light_8_Solar_Cell   -  I have been modifying a lot of solar garden and path lights for the last several years.  I buy some units from home improvement stores, then I gut them completely.  I take out the battery, electronic control board, LED and solar panel.  I then replace those components with new units.  I increase the size of the solar panel and battery.  I use a more efficient and brighter LED . . . Hobby Circuit by David Johnson P.E.-September 22, 2017

LED_Light_for_Tool_Shed   -  I have a lean-to 8ft by 12ft shed next to my house.  It is full of lawn chemicals and garden supplies.  There were times when I needed to get something from inside the shed during the dead of night.  Early on I had to use a flashlight.  But later, I installed a series of five 12v LED light strips on the ceiling.  Each strip contained 15 3v white LEDs.  The strip had 5 strings of three LEDs, wired in series, with a 150 ohm current limiting resistor. . . . Hobby Circuit by David Johnson P.E.-July 14, 2017

Light Detector   -  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

Light Intensity Monitor   -  For an on-going consulting project, I had to determine the light output decay time of different fluorescent lamps.  I wanted to know how fast the light from a lamp dropped to a low level, after current was interrupted in the lamp.  I used a high voltage . . . Hobby Circuit designed by David Johnson P.E.-April 01, 2005

Light Monitor Circuit   -  The circuit below takes advantage of a low power op amp with a “rail to rail” feature.  The single resistor R1 defines the light sensitivity of the circuit.  The output voltage is directly proportional to the intensity of light striking the small photodiode . . . Hobby Circuit designed by David A. Johnson P.E.-September 01, 2010

Light Output Intensity Meter   -  This circuit uses a large 1cm X 1cm silicon PIN photo diode and a transimpedance amplifier to measure the light power output of infrared and visible LEDs and laser diodes. It can be modified to produce almost any milliwatts to volts scale factor. It can b . . . Hobby Circuit designed by David A. Johnson P.E.-July 08, 2000

Light Pulse Receiver (2uS)   -  Although the LF357 is an obsolete part, this circuit gives you an idea how to build a sensitive modulated light detector with high ambient light immunity.  The first section uses a 100mH inductor as an efficient photodiode current to voltage conversion circuit . . . Hobby Circuit designed by David A. Johnson P.E.-June 03, 2002

Light Receiver 30Khz Amp   -  This circuit uses NPN darlington transistor to amplify the signal produced from short light flashes, as detected by a PIN photo diode.  The circuit draws only about 330uA from a 6v battery . . . Hobby Circuit designed by David Johnson P.E.-March 07, 2002

Light Receiver Amp-40Khz   -  This circuit is similar to 30KHZ LIGHT RECEIVER AMP  but provides more gain and operates up to 40KHz.  However it draws more power supply current.   . . . Hobby Circuit designed by David A. Johnson P.E.-March 07, 2002

Light Receiver Front-End Circuit   -  if you want even more sensitivity than the above circuit, try this design.  When used with a one centimeter square photodiode, you can achieve a range of several hundred feet with a standard TV or VCR remote control module.  Note: The LF357 operational amplifier is no longer available this circuit is for reference only.   . . . Hobby Circuit designed by David A. Johnson P.E.-March 12, 1999

Light Receiver-10MHz to 20MHz   -  Light power to volts conversion = APPROX.  15mV per microwatt at 850nM . . . Hobby Circuit designed by David A. Johnson P.E.-July 11, 2006

Light to Frequency Converter   -  This circuit uses a CMOS version of the classic 555 timer, to form a light intensity to frequency converter.  A small PIN photo diode is used as the light detector.  The pulses produced are short, so in some applications you may want to stretch them or . . . Hobby Circuit designed by Dave Johnson P.E.-August 31, 2006

Light, LED/Laser, Output Intensity Meter   -  This circuit uses a large 1cm X 1cm silicon PIN photo diode and a transimpedance amplifier to measure the light power output of infrared and visible LEDs and laser diodes.  It can be modified to produce almost any milliwatts to volts scale factor.  It can b . . . Hobby Circuit designed by David Johnson P.E.-July 08, 2000

Light_Pathway_1w_Solar_Cob_LED   -  Chip on board (COB) LEDs are all the rage.  These devices assemble multiple tiny LED chips onto a metal backed circuit board, then cover the assembly with a plastic cover.  The metal back allows the assembly to be mounted to heat sink to keep the device cool.  The multiple LED chips can be wired into any number of series/parallel configurations.  Some are wired for 12v operation while other COB LEDs in flashlights are all wired in parallel, with an operating voltage of about 3 volts. . . . Hobby Circuit by David Johnson P.E.-May 23, 2017

Lighthouse LED  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 Dave Johnson P.E.-July 11, 2006

Lighthouse_Solar_Powered   -  While at a discount store one day, I spotted an interesting tall lighthouse.  It had a tiny solar panel and an equally tiny LED light.  The LED was pointing downward, at the center of a rotating light reflector.  I thought it might be turned into an interesting addition to my wife’s garden. . . . Hobby Circuit by David Johnson P.E.-September 21, 2017

Limiting Amplifier-40Khz   -  This circuit has a gain of X20 at 40KHz.  The amplifier output level is limited to 2.5v peak to peak.  Limiting action begins with a 50v peak to peak input . . . Hobby Circuit designed by David Johnson P.E.-July 09, 2006

Line Powered High Intensity 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 . . . Hobby Circuit designed by David Johnson P.E.-December 07, 2008

Line Status Indicator for 1 Telephone Line   -  This circuit monitors one phone line . . . Hobby Circuit designed by Dave Johnson P.E.-June 10, 2000

Lithium Battery Tester   -  I bought some lithium ion rechargeable batteries a while back.  I was planning on using them to modify some solar powered LED spot lights.  What I like about these new batteries is that they are the same size as a standard 1.5v alkaline AA cell . . . Hobby Circuit designed by Dave Johnson P.E.-February 05, 2012

Lithium Ion Solar Battery Charger-#2   -  A single lithium ion battery cell needs 4.  2v from a current source to insure it is fully charged.    A solar panel with just enough individual cells wired in series to produce the needed voltage would be more efficient than one with more cells for a given surface area.    if you divide 4.  2 by eight you come up with a figure of 0.  525 volts . . . Hobby Circuit designed by Dave Johnson P.E.-May 21, 2013

LM317 adjustable voltage regulator used in Battery Eliminator Circuit   -  if you use a 1.5v or a 3v battery powered MP3 player for long periods of time, you may get tired of constantly changing batteries.  Some older players do not work will NiMH rechargeable batteries so changing out batteries can get expensive.  The circuit be . . . Hobby Circuit designed by David A. Johnson P.E.-June 01, 2005

Locate a Plastic Pipe   -  I used this circuit once to track down the location of a plastic pipe, buried underground.  It transmits a weak RF signal, which can be picked up by a portable AM radio from about 6 feet away . . . Hobby Circuit designed by David A. Johnson P.E.-December 18, 2004

Low Current Flashing LED Power Indicator   -  This circuit flashes a power indicator LED to keep the average current low . . . Hobby Circuit designed by Dave Johnson P.E.-June 04, 2000

Low Pass Filter, 3Khz, with an Audio Amp   -  This circuit uses a switched capacitor filter IC from National Semiconductor to filter signals with frequencies higher than the 3KHz needed for voice audio.  The schematic includes an audio amplifier that is designed to drive a standard audio head phone . . . Hobby Circuit designed by Dave Johnson P.E.-June 04, 2000

Low Power 12,000 Volt Power Supply   -  if you need about 12, 000 volts DC for an ion generator this circuit might be the ticket.  It draws power from the 120vac power line but it uses a small 6KV camera flash trigger coil.  The output signal is isolated from the power line . . . Hobby Circuit designed by David Johnson P.E.-March 27, 1999

Low Power LED Flasher   -  Judging from the numerous references I have received, this electronic circuit, hobby circuit seems to be rather popular.  Many published circuits which flash LEDs need 3 or more volts.  This electronic circuit uses only a single inexpensive C-MOS IC and . . . Hobby Circuit designed by David A. Johnson P.E.-June 04, 2000

Low Power Sequential Flasher using 10 LEDs   -  A while back I posted a flasher circuit which flashed 10 LEDs sequentially.  That circuit was powered by four AA alkaline cells.  The circuit below operates much the same way but has been modified to run from a single 3v CR2032 lithium coin cell . . . Hobby Circuit designed by David Johnson P.E.-April 17, 2011

Low Voltage Indicator for Lead-Acid Battery   -  Lead-acid batteries should not be discharged below a certain voltage.  Discharging a cell below about 1.  8v and can often damage it, which will result in a lower amp-hour capacity.  Large battery banks are critical in off-grid energy storage systems.  One . . . Hobby Circuit designed by David A. Johnson P.E.-July 30, 2006


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


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