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Circuits designed by David Johnson, P.E.
Last Updated on: Monday, July 11, 2016 01:59 PM

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Switch Circuits

Dave's Switch Circuits:  Page 1,   Page 2,   Page 3,    Page 4Page 5


1 Watt Fluorescent Lamp Night Light  -  If you are tired of replacing small night light lamps, try this circuit. The line powered circuit uses a long life cold cathode fluorescent lamp. A simple charge pump technique runs the lamp without any transformer . . . [Circuit by David Johnson P.E.,  03/26/99]


1.5V Touch Activated Switch  -  A single 1.5v silver oxide button cell powers this complete touch activated switch circuit for 5 years.  It features both a normally open and a normally closed set of solid-state switch thermals.  It also has an adjustable sensitivity, which can be set for a touch capacitance change as small as 1 picofarad. . . . [Circuit by Dave Johnson P.E.,  01/18/02]

10 LED Sequential Flasher using Low Powr  -  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 . . . [Circuit by Dave Johnson P.E.,  04/17/11]


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.,  06/30/08]


120 VAC Touch Switch  -  This is a capacitance based touch on/touch off switch, which can control power to a 200 watt 120vac load . . . [Circuit by David Johnson P.E.,  07/11/06]


12v – 24v AC and 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 Dave Johnson P.E.,  03/25/12]


12v Light/Dark Lamp Switch  -  At night, this circuit will route current to a 12v lamp, turning it on . . . [Circuit by David Johnson P.E.,  07/09/06]


12v Touch Switch Exciter Circuit  -  This circuit is designed to generate a 20KHz pseudo sine wave signal that can power about 50 remote touch activated switch circuits.  It can support a cable length of about 2500 feet.  A typical remote switch circuit is also shown as well as a receiver circuit for those switches. . . . [Circuit by David A. Johnson P.E.,  02/10/02]


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.,  07/09/06]


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.,  11/06/08]


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 Johnson P.E.,  12/26/10]


240VAC Touch Switch  -  This is another capacitance based touch on/touch off switch, which can control power to a 200 watt 240vac load . . . [Circuit by David Johnson P.E.,  07/11/06]


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.,  10/12/11]


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 Dave Johnson P.E.,  11/14/10]


3-Minute Closet Light  -  I have a coat closet by my front door.  The thing is very dark at night and really needs some kind of illumination inside.  I could hire an electrician to install a light in the closet ceiling and then wire it to a toggle switch outside the door but that would cost me quite a bit of money . . . [Circuit by David Johnson P.E.,  12/25/11]


3-Minute Closet Light #2  -  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 is only a few microamps.  A set of fresh batteries should last at least 200 light applications.  The circuit uses a Schmitt trigger inverter and two transistors.  When the pushbutton switch S1 is pressed, the 10uF capacitor C1 is discharged . . . [Circuit by Dave Johnson P.E.,  11/14/10]


3v Capacitance Proximity Switch  -  This circuit was designed to provide a touch activated switch function without an external power supply.  It draws so little power that a single 3v battery will operate the circuit for many years . . . [Circuit by Dave Johnson P.E.,  02/12/02]


5 Volt 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 David A. Johnson P.E.,  03/12/02]


5v Capacitance Touch Activated Momentary Switch  -  This circuit is discussed in more detail in the section on Capacitance Proximity Switch Technology. The circuit is powered from a standard +5v supply. It has both a source and sink output that change state whenever a metal button connected to the circuit . . . [Circuit by David Johnson P.E.,  07/08/00]


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 Dave Johnson P.E.,  03/12/02]


5w Fluorescent Lamp Intensity Modulator  -  The circuit was designed to experiment with using small fluorescent lamps as a broad pattern source of modulated light. The circuit hits the small lamp with narrow 1us pulses at a rate of 10KHz. Each pulse launches about 10 watts of visible light. The lamp . . . [Circuit by David Johnson P.E.,  06/27/00]


60 Watt Lamp With Auxiliary 14v LED 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 . . . [Circuit by Dave Johnson P.E.,  07/09/06]


6V to 24V DC Day/Night Switch  -  Using an inexpensive phototransistor, this circuit switches 12v to 24v power to a load, whenever the sun goes down . . . [Circuit by Dave Johnson P.E.,  07/09/06]


AC to DC (240v to 5v)Power Supply  -  This is simple way to power some 5v logic from a 240vac source.  If a 120vac power adapter is used, the circuit will also work for 120vac power lines . . . [Hobby Circuit designed by David A. Johnson P.E.,  02/12/02]


AC/DC relay from Charge Coupled MOSFET  -  This circuit acts as an AC/DC relay with a rating up to 50 volts peak and up to 10 Amps of current.  The differential oscillator supplies voltage to the gates of the two FETs with good isolation will drawing only 1.5ma of current . . . [Hobby Circuit designed by David Johnson P.E.,  10/16/05]


Alarm-Piezo Device detects Motion  -  Using a piezo device, this circuit will activate a beeper whenever the circuit is moved.  It could be used as an earthquake alarm . . . [Circuit by Dave Johnson P.E.,  07/09/06]


Audio Activated Switch  -  This circuit will activate a transistor switch when it detects at least 50mv peak to peak of an audio signal.  It could be used to turn on a relay, routing the signal to were it is needed. . . . [Circuit by Dave Johnson P.E.,  07/09/06]


Dave's Switch Circuits: 
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