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DiscoverCircuits.com -- Hobby Corner
Last Updated on: Saturday, December 30, 2017 02:50 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


0.5v to 6v Voltage Converter   -  Conventional silicon transistors just can't operate at voltages less than about 0.  7v.  Old germanium transistors could be used, but those are hard to find these days and most are rather large in size.  Some new n-channel MOSFET devices with very . . . Hobby Circuit designed by David Johnson P.E.-May 21, 2007

0VAC to 280VAC Variable Isolated AC Voltage   -  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 . . . Hobby Circuit designed by Dave Johnson P.E.-July 08, 2000

1 Second One Shot Circuit   -  This timer circuit draws only 3ua of current, and can be powered by DC supplies ranging from 3v to 15v.  The circuit produces accurate pulses whose time can easily be adjusted, based on the R1 x C1 time constant.  The time should not change,  . . . Hobby Circuit designed by David A. Johnson P.E.-September 02, 2010

10 Turn Pot Forms Frequency Readout   -  Let’s say you are designing a signal generator for a test fixture.  To adjust the frequency you would like to use a ten turn pot with a nice dial mechanism attached as a frequency display.  However, a display range of 0 to 9.  99 would be impractical since . . . Hobby Circuit designed by David A. Johnson P.E.-January 27, 2008

100Khz Low Power Light Receiver   -  By starving a high speed logic inverter for current, this circuit can produce a sensitive 100KHz light receiver circuit, which is immune to ambient light, but only drawing 100 microamps from a 3 volt supply . . . Hobby Circuit designed by Dave Johnson P.E.-April 17, 2005

12 Volt Lite/Dark Lamp Switch   -  Often, for certain low voltage lighting systems; you would like to turn off the lights during the bright light of the day.  Most commercial day/night switches are designed for AC lighting.  The circuit below was designed for a 12v DC system.  But, it could be modified for other voltage as well.  It uses an inexpensive phototransistor as the light detector.   . . . Hobby Circuit designed by David Johnson P.E.-June 30, 2008

120 VAC / 240 VAC Indicator   -  Two LEDs indicate if a power line has 120vac or 240vac voltage on it . . . Hobby Circuit designed by David Johnson P.E.-July 09, 2006

125KHZ Medium Power Oscillator   -  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 Johnson P.E.-March 12, 2002

125khz Oscillator with Medium Power   -  This circuit 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

125Khz Ultra Pure Sine Wave Signal Source   -  For some RFID systems operating at 125KHz, a very low distortion signal source reference is needed.  The circuit shown on this page produces a 10-volt peak-to-peak signal into a 50-ohm load, with a distortion of only 0.  01% . . . Hobby Circuit designed by David Johnson P.E.-February 11, 2002

12kv High Voltage Generator   -  The hobby circuit below uses an unusual method to generate about 12, 000 volts with about 5uA of current.  Two SCRs form two pulse generator circuits.  The two SCRs discharge a 0.  047uF a 400v capacitor through a xenon lamp trigger coil at 120 times a second . . . Hobby Circuit designed by David A. Johnson P.E.-March 27, 1999



12v Battery Voltage Monitor-Expanded Scale    -  The circuit below expands the battery voltage monitoring scale for a 12v battery so a more accurate voltage reading can be made.  The numbers printed onto the face of a standard 0v to 5v meter are changed so the scale ranges from 10v to 15v . . . Hobby Circuit designed by Dave Johnson P.E.-October 16, 2005

12v Brush Motor Speed Controller   -  in many applications, you would like to hold the speed of a motor constant, even as variations in the power supply voltage or mechanical load try to change its speed.  In other applications, the average current to the motor needs to be limited, so the . . . Hobby Circuit designed by Dave Johnson P.E.-May 05, 2007

12v DC Motor with Logic Controlled Automatic Brake   -  There are times when you would like to control a DC motor using a simple +5v logic swing signal.  The circuit below performs this feat and also includes an automatic motor braking circuit.  When the input logic signal swings from 0v to +5v, the n-channel . . . Hobby Circuit designed by David Johnson P.E.-February 18, 2010

12v_To_24v_Solar_Battery_Charger   -  A while back I received an email from a Discover Circuits visitor.  He wanted to know how he could use a single 12v solar panel to charge a 24v lead acid battery bank.  He said he used the 24v battery to run an emergency 120vac power system.   By using the higher 24 volts instead of 12v, his DC to AC inverter could pump out more peak power, for starting things like well pumps and window air conditioners. . . . Hobby Circuit by David Johnson P.E.-July 23, 2017

12v-24v AC & DC Day/Night Switch   -  The circuit uses a bridge rectifier circuit to convert AC into DC.  A 12v zener diode limits the operating voltage of the circuit to 12v.  A tiny Schmitt trigger inverter and a phototransistor detects the ambient light intensity.  If there is sufficient light, the inverter disables a push-pull oscillator circuit . . . Hobby Circuit designed by David A. Johnson P.E.-March 26, 2012

14v LED AuxiliaryLamp with a 60 Watt Lamp   -  This circuit controls power to a standard 60 watt lamp plus generates an auxiliary 14v DC supply which can power an automotive style 12 LED array . . . Hobby Circuit designed by David Johnson P.E.-June 27, 2000

175Khz Inductive Pulse Transmitter   -  This circuit is discussed in more detail in the Experimenters Journal.  The transmitter’s six-inch diameter coil launches powerful magnetic 175KHz ring pulses that can be detected by the circuit below . . . Hobby Circuit designed by David A. Johnson P.E.-June 27, 2000

1Khz to Over 70Mhz 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 . . . Hobby Circuit designed by David Johnson P.E.-June 11, 2000

1-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 David Johnson P.E.-September 26, 2009

1us LED Pulse Driver + Voltage to Frequency Converter   -  This circuit receives the signal from the above amplifier and launches powerful 1uS infrared light pulses from a low cost LED that are frequency modulated by the audio information.  The 10KHz center frequency of the pulse stream is low enough so a standard . . . Hobby Circuit designed by David A. Johnson P.E.-March 22, 1999

1us Light Pulse Discriminator   -  This circuit is designed to detect the narrow 1uS pulses produced by the above amplifier circuit.  The clean logic type pulses produced by the discriminator are then sent to a frequency to voltage converter.  The circuit is designed to process a pulse frequency . . . Hobby Circuit designed by Dave Johnson P.E.-March 11, 1999

1us Light Pulse Receiver   -  This circuit is designed to detect very weak light pulses lasting 1uS.  It uses a tuned LC feedback network to provide high sensitivity while giving high ambient light immunity.  A post voltage amplifier is included with a gain of about X20 . . . Hobby Circuit designed by Dave Johnson P.E.-March 11, 1999

1W 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 Dave Johnson P.E.-November 06, 2008

1w_Solar_Path_Light_Using_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

2 Pushbutton Motor Controller   -  Two small pushbutton switches, a few diodes and two relays form a method to control on/off power to a brush motor as well as the motor direction.  The circuit was originally designed for a motorized lifting platform . . . Hobby Circuit designed by David Johnson P.E.-February 11, 2002

2-12v Battery Isolator Circuit with a LTC4412   -  Has just announced a neat little chip (LTC4412).  It has been designed to be used in conjunction with an external P-channel power FET, to form an ideal diode function with a very low 0.  05v voltage drop.  The chip monitors the voltage on eit . . . Hobby Circuit designed by David A. Johnson P.E.-August 07, 2006

24 Volt Day Night Switch   -  Many low voltage outdoor lighting systems use 24vac to power the devices.  The low voltage is much safer to use outside than standard 120vac or 240vac power systems.  The circuit below is designed to turn off power to outdoor lights during daylight and turn them back on at night . . . Hobby Circuit designed by David A. Johnson P.E.-December 26, 2010

24 Volts AC to 24 Volts DC Power Supply   -  The idea for the circuit below came from a company needing to power several 24v DC LED assemblies from an existing 24vac supply.  They did not need a rock solid and regulated 24 volts but a voltage which hovered around that voltage.  Running the AC through . . . Hobby Circuit designed by David Johnson P.E.-February 19, 2011

24V DC Powered Beeper with 4 Separate Inputs   -  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 Dave Johnson P.E.-December 19, 2009

24v NiMH Battery Charger using a 12v Solar Panel    -  A while back I received an email from a guy in the UK.  He wanted to use a small solar panel, designed to charge 12v lead acid batteries, but use it to charge a 24v battery pack.  His 24v battery pack used 20 AA size NiMH cells.  He went on to explain that his 20 cell NiMH battery pack was used very infrequently . . . Hobby Circuit designed by David Johnson P.E.-October 12, 2011

24-Volt AC Powered 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.     . . . Hobby Circuit designed by David Johnson P.E.-July 29, 2009

2Mhz Broad Band Optical Fiber Receiver   -  if you need more sensitivity than the above circuit this circuit provides about ten times more gain.  It too is designed around an inexpensive plastic optical fiber detector . . . Hobby Circuit designed by David A. Johnson P.E.-June 09, 2000

3 Minute LED Closet Light   -  The circuit below is powered by three 1.5v alkaline AA cells.  With a finger tap to the pushbutton trigger switch, a cluster of 6 wide angle white LEDs is turned on. The lights remain on for about 3 minutes, then will turn off.  The circuit’s standby current . . . Hobby Circuit designed by David Johnson P.E.-November 14, 2010

30 LED Night Light   -  This Hobby Circuit uses a capacitor to limit the current through a series-parallel string of 30 LEDs.  15 LEDs are wired in series in one direction and 15 more in the other direction.  The capacitor limits the average current to about 20ma.  The 100 ohm metal oxide resistor acts as a fuse.   . . . Hobby Circuit designed by David A. Johnson P.E.-January 00, 1900

3Khz Filter + Audio Amplifier   -  This circuit is the audio amp section for a complete optical transmitter.  The circuit amplifies and filters the voice audio signals from an electret microphone.  The circuit is described in more detail in . . . Hobby Circuit designed by David Johnson P.E.-June 04, 2000

3mw Laser Test-20Mhz VCSEL   -  This circuit takes advantage of some new vertical cavity surface emitting lasers (VCSEL) that don’t require light output control circuits.  The circuit shows how to drive the device from a single high speed CMOS IC  . . . Hobby Circuit designed by Dave Johnson P.E.-June 17, 2000

3v Powered Super Bright LED Flasher   -  I have posted several kinds of LED flashers over the years.   This is yet one more flasher, designed to flash any high power LED of any color.  It hits the LED with a 25ms 250ma pulse once every 2 seconds.   This works out to an average current about 3ma.  It . . . Hobby Circuit designed by David Johnson P.E.-April 22, 2009

3v Universal LED Flasher   -  This low power LED flasher circuit draws about 100ua from any DC power supply ranging from 3 volts to 24 volts.  The 1.  0Hz 10ms LED pulsed current is held to a constant 10ma . . . Hobby Circuit designed by David Johnson P.E.-July 11, 2006

4 to 20ma Current Loop Senses Temperature   -  I designed a circuit similar to this one years ago to accurately measure the air temperature inside a building 1000s of feet from a control room.  The circuit uses a very robust current loop method.  It uses a highly accurate semiconductor temperature sensor . . . Hobby Circuit designed by Dave Johnson P.E.-July 04, 2006

4_D-Cell_LED_Lantern_Modified   -  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. . . . Hobby Circuit by David Johnson P.E.-September 21, 2017

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 . . . Hobby Circuit designed by Dave Johnson P.E.-June 04, 2000

40KHz Light Detector with Sunlight Immunity   -  This hobby circuit below was designed to turn on an external 12v relay, whenever it detects light from a nearby LED light source, modulated at 40KHz to 50KHz.  This circuit was originally designed to operate from a fast moving vehicle . . . Hobby Circuit designed by David Johnson P.E.-February 08, 2007

40Khz Precision Triangle Generator   -  This circuit generates a precision 40KHz triangle waveform . . . Hobby Circuit designed by David A. Johnson P.E.-July 09, 2006

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

5+V Classic Linear Supply using 6.3VAC Transformer   -  A classic method for producing a regulated +5v DC supply is shown below.  This circuit consists of an iron core transformer, a bridge rectifier, a filter capacitor and a voltage regulator.  Many people are tempted to use a very popular 6.  3v transformer . . . Hobby Circuit designed by Dave Johnson P.E.-February 14, 2009

50ua Current Drives Solid State Relay Requires Only   -  Most solid state relays require at least 5ma and often more input control current, to fully turn on the device.  But such current levels often force battery powered circuits to use excessively large batteries.  The relay hobby circuit shown below demands only 50uA of input current . . . Hobby Circuit designed by Dave Johnson P.E.-June 03, 2000

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 . . . Hobby Circuit designed by Dave Johnson P.E.-July 15, 2009

5v 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.   . . . Hobby Circuit designed by David A. Johnson P.E.-March 12, 2002

60hz Clock Generator is Line Powered   -  This circuit is connected to the 120vac power line and transfers 60Hz clock pulses to a logic circuit. The optoisolator used provides 5000 volts of isolation between the power line and the logic side of the circuit . . . Hobby Circuit designed by David Johnson P.E.-February 23, 1999


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


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