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Circuits designed by David Johnson, P.E.
Last Updated on: Thursday, April 07, 2016 02:04 PM

Master Category List - Dave's Circuits

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Infrared Circuits

125khz Wireless Smart Key Detector  -  This circuit will turn on an indicator light whenever it detects a smart car key containing an RFID chip . . . [Circuit by David Johnson P.E.,  07/11/06]


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 Johnson P.E.,  03/22/99]


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.,  06/04/00]

Boost Infrared TV/VCR Remote Signal  -  This circuit will boost the signal from any infrared TV or VCR remote, extending the range by a factor of 3X.  . . . [Hobby Circuit designed by David Johnson P.E.,  10/05/05]


Color Film Makes Optical Filter  -  This isnít 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 . . . [Circuit by Dave Johnson P.E.,  01/01/98]


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.,  10/05/05]


IR 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.  . . . [Hobby Circuit designed by Dave Johnson P.E.,  10/05/05]


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.,  06/04/00]


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 A. Johnson P.E.,  02/15/02]


Optical Filter using Color Film Negative  -  This isnít 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 Dave Johnson P.E.,  01/01/98]


Optical RFID Test Circuit  -  I designed this test the concept of using light techniques to send identification data instead of RF. A more detailed discussion on this scheme can be found in the Imagineered new products section . . . [Circuit by David Johnson P.E.,  02/11/02]


Piezoelectric Tap Switch  -  This circuit uses a flat piezo wafer, glued inside a plastic box, as a finger tap sensor.  With each tap of a finger to the box holding the wafer, the circuit turns on and off AC or DC power to an external device.  The circuit is powered by a 9v battery . . . [Circuit by David A. Johnson P.E.,  12/07/10]


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 David Johnson P.E.,  07/09/06]


RFID Test Circuit  -  I designed this test the concept of using light techniques to send identification data instead of RF. A more detailed discussion on this scheme can be found in the Imagineered new products section . . . [Hobby Circuit designed by David Johnson P.E.,  02/11/02]


Solar Powered Infrared 1W Security Camera Illuminator  -  Many security cameras are equipped with an array of infrared LEDs to illuminate an area in front of the camera with invisible light for night time surveillance.  However, there are times when a remote area, well away from the camera, needs additional infrared light.  The circuit below uses a modified solar powered path light to bathe a fairly large area with 850nm infrared light . . . [Circuit by David A. Johnson P.E.,  06/22/14]


Use Color Film Negative to Make An Optical Filter  -  This isnít 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.,  01/01/98]


Voltage to Frequency Converter + 1us LED Pulse Driver  -  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 . . . [Circuit by David A. Johnson P.E.,  03/22/99]


Wireless RFID Smart Key Detector  -  Many cars now use a key with an imbedded RFID microchip.  The microchip is read when the key is inserted into the carís ignition.  The keys containing a microchip often look the same as most other keys. People duplicating car keys will often not know of the microchip.  This circuit will light a LED if it detects a key containing a 125KHz RFID chip. . . . [Hobby Circuit designed by David A. Johnson P.E.,  07/09/06]


 
20Mhz VCSEL 3mw Laser Test Circuit  -  This circuit takes advantage of some new vertical cavity surface emitting lasers (VCSEL) that donít require light output control circuits. The circuit shows how to drive the device from a single high speed CMOS IC . . . [Circuit by David Johnson P.E.,  06/17/00]


 
3mw Laser Test-20Mhz VCSEL  -  This circuit takes advantage of some new vertical cavity surface emitting lasers (VCSEL) that donít require light output control circuits. The circuit shows how to drive the device from a single high speed CMOS IC . . . [Hobby Circuit designed by David A. Johnson P.E.,  06/17/00]


 
40khz TV-VCR Light Source Repeater  -  This circuit is designed to be placed directly in front of a standard TV or VCR remote. The exiting light pulses produced by the circuit match the pulses from the remote but are about 10 times more powerful. Using the device, the remote can operate a TV or VCR over three times the normal distance . . . [Circuit by David Johnson P.E.,  06/04/00]


 
Detects Shadow Activated Motion  -  This circuit can sound an alarm when the shadow of a hand or arm moves over  two small photo diodes . . . [Circuit by David A. Johnson P.E.,  08/21/05]


 
Finger Touch Activated Switch  -  It does not get any easier if you want a solid state switch that is activated by the touch of a finger. Two small metal pins route voltage through the finger skin to a MOSFET switch. The circuit is great for situations where a membrane type mechanical switch . . . [Circuit by David Johnson P.E.,  06/03/00]


 
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 Johnson P.E.,  07/09/06]


 
Infrared Remote Extender Circuit  -  This circuit is designed to be placed directly in front of a standard TV or VCR remote. The exiting light pulses produced by the circuit match the pulses from the remote but are about 10 times more powerful . . . [Hobby Circuit designed by David Johnson P.E.,  06/04/00]


 
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 Johnson P.E.,  07/11/06]


 
Light/Dark Activated Motion Detector  -  This circuit can sound an alarm when the shadow of a hand or arm moves over  two small photo diodes . . . [Circuit by Dave Johnson P.E.,  08/21/05]


 
Optical Filter using Color Film Negative  -  This isnít 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 Johnson P.E.,  01/01/98]


 
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 David A. Johnson P.E.,  07/09/06]


 
Remote Extender Circuit  -  This circuit is designed to be placed directly in front of a standard TV or VCR remote. The exiting light pulses produced by the circuit match the pulses from the remote but are about 10 times more powerful. Using the device, the remote can operate a TV or VCR over three times the normal distance . . . [Circuit by David A. Johnson P.E.,  06/04/00]


 
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 issue, I designed the circuit shown below.  The circuit taps into the TV remoteís 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 Dave Johnson P.E.,  12/14/00]


 
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 David Johnson P.E.,  07/11/06]


 
Scare Off Pigeons  -  I have an area on my roof where a large flock of pigeons like to roost.  Their nesting materials and droppings really make a mess. Often there is enough junk from them that it clogs my roof gutters.  Perhaps one way to scare them away . . . [Hobby Circuit designed by David A. Johnson P.E.,  04/01/05]


 
Shadow Activated Motion Detector  -  The hobby 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 device . . . [Hobby Circuit designed by Dave Johnson P.E.,  08/21/05]


 
Short Range Reflective Object Sensor  -  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.,  07/09/06]


 
TV /VCR Remote Range Extender Circuit  -  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 issue, I designed the circuit shown below.  The circuit taps into the TV remoteís existing infrared LED and drives 8 more efficient devices.  The result is a communications range some 4 to 5 times longer. . . . [Circuit by David Johnson P.E.,  10/05/05]


 
TV-VCR Light Source 40Khz Repeater  -  This circuit is designed to be placed directly in front of a standard TV or VCR remote. The exiting light pulses produced by the circuit match the pulses from the remote but are about 10 times more powerful . . . [Hobby Circuit designed by Dave Johnson P.E.,  06/04/00]


 
Use Color Film Negative to Make An Optical Filter  -  This isnít 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 Dave Johnson P.E.,  01/01/98]


Infrared Circuits

Master Category List - Dave's Circuits


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