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Relay Circuits
#'s - K         L - R          S - Z


Last Updated: October 24, 2017 02:55 PM
Circuits Designed by Dave Johnson, P.E. :

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, 2017

Light Receiver Works from 1Khz to Over 70Mhz - 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. . . Circuit by David Johnson P.E.-June, 2000

Low Voltage Latching Relay Driver - Using some small super capacitors, this circuit can latch and unlatch a mechanical relay with 10 amp contacts, from a small 3 volt power source.  By using a latching relay, power can be controlled to a load with a tiny battery. . . Circuit by David Johnson P.E.-August, 2006

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 David Johnson P.E.-December, 2009

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 Johnson P.E.-December, 2010

Piezoelectric Triggered Switch - Two different switch circuits are shown.  One sources current and the second sinks current.  Both switches are connected to a piezo wafer.  When the wafer is tapped, the switches are activated. . . Circuit by David Johnson P.E.-February, 2002

Pushbutton Switch Through Glass  - This simple technique allows a mechanical pushbutton switch assembly to activate a reed type relay through a pane of thick glass.  Pushing the button moves a magnet near the reed relay, closing the relay contacts . . . Hobby Circuit designed by Dave Johnson P.E.-February, 2002

Pushbutton Switch works through Glass - This simple technique allows a mechanical pushbutton switch assembly to activate a reed type relay through a pane of thick glass.    Pushing the button moves a magnet near the reed relay, closing the relay contacts.. . . Circuit by Dave Johnson P.E.-February, 2002

Capacitance Proximity Switch
Draws very low power - Ideal for battery-powered applications
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Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:

Low Voltage Latching Relay Driver - Using some small super capacitors, this circuit can latch and unlatch a mechanical relay with 10 amp contacts, from a small 3 volt power source.  By using a latching relay, power can be controlled to a load with a tiny battery. . . Circuit by David Johnson P.E.-August, 2006

Latching Relays -  Find out about latching relays and their uses.   __ Designed by REUK-Renewable Energy UK website

LED Relay Timer -  This circuit provides a visual 9 second delay using a 7 segment digital readout LED.  When the switch is closed, the CD4010 up/down counter is preset to 9 and the 555 timer is disabled with the output held high.  When the switch is opened,  __ Designed by Bill Bowden

Light / dark activated relay -  The potmeter adjust the trigger 'on' level.  The diode in the diagram shows to be 1N914.  This is ok if you have a light-duty relay, also the 1N914 is a signal diode so actually does not qualify.  Use a 1N4001 (Tony van Roon's or better) instead.  A couple of substitutes for the 2N2222 transistor are: NTE123A, ECG123A, PN100, etc __ Designed by Tony van Roon  VA3AVR

Light Activated Relay -  This is same circuit as above with the addition of a photo resistor to trigger the flip flop instead of a push button.  The bias resistor in series with photo resistor was chosen so that sufficient voltage is present at the base of the 2N3904 to supply current to the circuit in ambient lighting conditions __ Designed by Bill Bowden

Light Activated Relay with 555 IC -  This light activated relay circuit presented here uses the 555 timer IC and a light dependent resistor or LDR to form a light sensitive relay in an intruder alarm system or for switching on a lamp at Sun set and off at Sun rise.  Potentiometer R1 value must be chosen and then adjusted that under normal conditions when the light __ Designed by Popescu Marian

Light Controlled Relay Switch -  The first circuit energizes the relay when the light rises above the preset level.  The second circuit energizes the relay when the light falls below the preset level.  The two circuits are practically identical.  The only difference between them is the polarity of the transistor.  The value of the LDR is not critical.  The important thing is the voltage on pins 5 & 6.  Any value LDR should work satisfactorily.  But you may need to change the value of R1 - to achieve the desired range of adjustment __ Designed by Ron J

Light Receiver Works from 1Khz to Over 70Mhz -  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. . . Circuit by David Johnson P.E.-June, 2000

Light Sensor-741 Based -  The circuit as shown act as a light sensor.  Under normal conditions the resistance of the LDR is high, keeping pin 2 low.  When light falls onto the LDR the resistance drops to a couple hundred ohms and triggers pin 2 high which biases the base of Q1 via pin 6 and R4 and in turn activates the relay __ Designed by Tony van Roon  VA3AVR

Light/Dark Detector drives a relay -  This handy little circuit can tell the difference between darkness and light, making it very useful for switching on and off signs, porch lights or other things when it gets dark or light.   __ Designed by Aaron Cake

Long Duration Relay-1 min to 20 hrs -  This is an accurate long-duration time delay driver, switchable between 1 and 10 minutes or 10 to 100 minutes and whose function does not depend on electrolytic capacitors.  Film dielectric caps have been selected.  IC 1 is configured as a free-running astab __ Designed by Tony van Roon  VA3AVR

Low Voltage Latching Relay Driver -  Using some small super capacitors, this circuit can latch and unlatch a mechanical relay with 10 amp contacts, from a small 3 volt power source.  By using a latching relay, power can be controlled to a load with a tiny battery. . . Circuit by David Johnson P.E.-August, 2006

Lua Sonoff relay WiFi ESP8266 -  Lua application for management Sonoff WiFi Smart Switch, there is no need cloud, broker or third party server.  The program was tested with the device Sonoff, which you see in the picture, but it is likely that it will also work with older versions Sonoff modules or smart socket. __ Designed by © Pavel Janko

Mains Power Load Sensing Automatic Switch -  WARNiNG:  This circuit requires experience with mains wiring.  Do not attempt construction unless experienced and capable.  Death or serious injury may result from incorrect wiring.   __ Designed by Rod Elliott  ESP

Maximizing the Life Span of Your Relays 5988-6917EN -  Application Note__ Aligent

Modular Relay System -  This is simple transistorised relay into which can be plugged 'personality modules' to turn the base unit into a timer (pulse, delay on energise or delay on de-energise) or a latching relay or whatever is required.  This is therefore a universal relay system.  it was designed to simplify industrial machinery control.   __ Designed by Richard Torrens

Motorcycle Alarm #7 -  Motorcycle Alarm Circuits:  This is a simple transistor alarm - with a siren cut-off timer.  While the thief continues to move the bike - and the normally-open trigger switch continues to open and close - the siren will continue to sound.  Shortly after the bike stops moving - the siren switches off - and the alarm resets.  __ Designed by Ron J.

Motorcycle Alarm #8 -  Motorcycle Alarm Circuits:  This transistor alarm has a siren cut-off timer - and an LED activation indicator.  Shortly after the thief abandons the bike - the siren will switch off and the alarm will reset.  if the LED is lighting when you return - you'll know there's been an activation while you were away.  __ Designed by Ron J.

Multiple Relay Drive -  Circuit ideas for Designers App Note__ Advanced Linear Devices, Inc

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 David Johnson P.E.-December, 2009

One oscillator drives multiple solid-state relays -  16-Mar-06 EDN Design Ideas:  A conventional electromechanical relay often makes sense for switching large amounts of load current on and off and when proportional control of the load’s current or voltage is unnecessary __ Circuit Design by Juan Ramón Vadillo Pastor, SOR Internacional SA, Saint Quirze Del Valles, Barcelona, Spain

One Shot Multivibrator Timer Relay -  This circuits shows a pair of CMOS NOR gates which form a push-button-activated one-shot multivibrator relay-switching circuit that provides delays up to several  minutes with reasonable accuracy. __ Designed by Tony van Roon  VA3AVR

Parallel Port Relay Interface -  Below are three examples of controlling a relay from the PC's parallel printer port (LPT1 or LPT2).  Figure A shows a solid state relay controlled by one of the parallel port data lines (D0-D7) using a 300 ohm resistor and 5 volt power source.  The solid state relay will energize when a "0" is written to the data line.  Figure B and C show.   __ Designed by Bill Bowden

PC Securely Controls Relay -  11/23/95 EDN Design Ideas:  When a PC-driven solid-state or electromechanical relay controls external equipment, take care to design an interface that avoids false triggering.  The interface circuit in Figure 1a switches the relay on and off only after a specific sequence of outputs.  Thus, this design protects the relay against the influence of computer-reset and i/O operations that some drivers perform during system start-up to locate add-on cards __ Circuit Design by Jerzy R Chrzaszcz, Institute of Computer Science, Warsaw University of Technology Warsaw, Poland

Photo Electric Street Light -  This is basically a Schmitt Trigger circuit which receives input from a cadmium sulfide photo cell and controls a relay that can be used to switch off and on a street lamp at dawn and dusk.  I have built the circuit with a 120 ohm/12 volt relay and monitored performance using a lamp dimmer, but did not connect the relay to an outside light.  The photo cell should be shielded from the lamp to prevent feedback and is usually mounted above the light on top of a reflector and pointed upward at the sky so the lamp light does not strike the photo cell and switch off the lamp.  The photo cell is __ Designed by Bill Bowden

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 Johnson P.E.-December, 2010

Piezoelectric Triggered Switch -  Two different switch circuits are shown.  One sources current and the second sinks current.  Both switches are connected to a piezo wafer.  When the wafer is tapped, the switches are activated. . . Circuit by David Johnson P.E.-February, 2002

Pinewood Derby Finish Line Detector -  The following is an electronic schematic and parts list for the items needed to construct an infrared detector for the finish line of a Pinewood Derby racetrack utilizing an external power supply and the parallel port of an iBM compatible computer of at least 486/33Mhz running DOS 3.1 or better.  Also included is a narration concerning the construction of the detector as well as the BASIC  code required to operate the detector.   __ Designed by Pack 471

Pinewood Derby Finish Line Lights -  The finish line circuit below detects the first of three cars to cross the line and illuminates a 25 watt 120 VAC lamp indicating the winning lane.  Three photo transistors are used which can be embedded into the track with a light shining down onto the finish line so that as the car crosses over the sensor, the light is blocked, activating the relay and lighting the lamp for the appropriate track.   __ Designed by Bill Bowden

Power-Off Time Delay Relay -  The two circuits below illustrate opening a relay contact a short time after the ignition or ligh switch is turned off.  The capacitor is charged and the relay is closed when the voltage at the diode anode rises to +12 volts.  The circuit on the left is a common collector or emitter follower and has the advantage of one less part since a resistor is not needed in series with the transistor base.  However the voltage across the relay coil will be two diode drops less than the supply voltage, or about 11 volts for a 12.5 volt input. __ Designed by Bill Bowden

Power-on sequencing using TL431 in comparator Mode -  TL431 as a comparator.  Delay timers.  Power-on sequencers.  TL431 without feedback can be considered as an NPN or N-MOS device with high transconductance and precise 2.5V turn-on voltage.  Tube heads beware: the upper (+supply) pin on TL431 is cathode, lower (-supply) , anodeit's another world.   __ Contact klausmobile @ yahoo.Com

Power-On Time Delay Relay -  Here's a power-on time delay relay circuit that takes advantage of the emitter/base breakdown voltage of an ordinary bi-polar transistor.  The reverse connected emitter/base junction of a 2N3904 transistor is used as an 8 volt zener diode which creates a higher turn-on voltage for the Darlington connected transistor pair.  Most any bi-polar transistor may be used, but the zener voltage will vary from about 6 to 9 volts depending on the particular transistor used.  Time delay is roughly 7 seconds using a 47K resistor and 100uF capacitor and can be reduced by reducing the R or C values. __ Designed by Bill Bowden

Power-Saving Relay Driver -  in many circuits, the switching action is performed by a relay, which in turn activates an external load.  The power consumed by the relay may be unsuitable for battery-powered applications.  Here...__ Electronics Projects for You

Protect outputs against overvoltage -  10/11/07 EDN Design Ideas:  Adding a solid-state relay and control circuitry to an amplifier's output provide as overvoltage protection __ Circuit Design by Dimitri Danyuk, Kiev, Ukraine

Pulse Relay -  Scroll to this one.  This circuit will convert a standard relay to a pulse relay; pressing the button will switch it on and pressing it again will switch it off.  For this purpose you need a relay with 2 sets of contacts: one is used for the circuit and the other is available for an outside circuit.  Sometimes it is difficult or impossible to find a stepping relay, normally used in electrical wiring, and this is a viable solution.   __ Designed by di Domenico Di Mario

Pulse relay Reduced Power Relay -  This circuit will convert a standard relay to a pulse relay; pressing the button will switch it on and pressing it again will switch it off.  For this purpose you need a relay with 2 sets of contacts: one is used for the circuit and the other is available for an outside circuit.  __  

Pushbutton Switch Through Glass  -  This simple technique allows a mechanical pushbutton switch assembly to activate a reed type relay through a pane of thick glass.  Pushing the button moves a magnet near the reed relay, closing the relay contacts . . . Hobby Circuit designed by Dave Johnson P.E.-February, 2002

Pushbutton Switch works through Glass -  This simple technique allows a mechanical pushbutton switch assembly to activate a reed type relay through a pane of thick glass.    Pushing the button moves a magnet near the reed relay, closing the relay contacts.. . . Circuit by Dave Johnson P.E.-February, 2002

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Relays#'s - K         L - R          S - Z

 


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