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


Last Updated: December 02, 2017 06:34 AM
Circuits Designed by Dave Johnson, P.E. :

Reduced Power Relay Driver - Relays can handle a lot of power.  However, for certain power sensitive designs you would like to reduce the power needed to hold a relay closed.  The circuit below performs such a task.  It uses a single CD4093 quad NAND gate.  When the on logic input. . . Circuit by David A. Johnson P.E.-August, 2008

Relay Driver with Reduced Power - Relays can handle a lot of power.  However, for certain power sensitive designs you would like to reduce the power needed to hold a relay closed.  The circuit below performs such a task.  It uses a single CD4093 quad NAND gate.  When the on logic input . . . Hobby Circuit designed by David Johnson P.E.-August, 2008

Remote Relay Driver - I received a call from a Discover Circuits visitor who wanted a simple way to turn on an outside lighting system using a low voltage control line.    I suggested the simple circuit below.    The circuit is powered by a 9v battery and uses a very efficient latching relay.    Two low voltage wires lead from the a toggle switch to the remote relay.    A toggle switch selects either the on or off condition of the relay.    The relay contacts are rated at 10 amps, so the small relay can handle a sizeable amount of power.. . . Circuit by Dave Johnson P.E.-April, 2014

Capacitance Proximity Switch
Draws very low power - Ideal for battery-powered applications
6 Models Available - Call 806-368-7747

Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:

Reduced Power Relay Driver -  Relays can handle a lot of power.  However, for certain power sensitive designs you would like to reduce the power needed to hold a relay closed.  The circuit below performs such a task.  it uses a single CD4093 quad NAND gate.  When the on logic input. . . Circuit by David A. Johnson P.E.-August, 2008

Relay Actuating Circuit with Millivolt Sensitivity -  Common electromagnetic relays with coil voltage of 5V, 6V or 12V can operate power circuits in the range of 250 to 300 volts and up to 20A.  The actuating current of...__ Electronics Projects for You

Relay Based Motorcycle Alarms -  Motorcycle Alarm Circuits:  These are two - easy to build - relay-based alarms.  You can use them to protect your motorcycle - but they have many more applications.  if you use relays with 6-volt coils - they'll protect your "Classic Bike".  Both alarms are very small.  The completed boards occupy about half a cubic-inch - 8 cc.  The standby current is zero - so they won't drain your battery.  __ Designed by Ron J.

Relay Boards -  Find out about relay boards - what they are, where to buy them, and how to use them.   __ Designed by REUK-Renewable Energy UK website

Relay card -  relay card interface circuit, german text  __ Designed by Frank Steinberg

Relay Delay -  This circuit waits for a set time and then activates a relay.  With the cap that is in the schematic you will get about a 6 sec delay till power on.  You can change the cap in this circuit to 470uF for about a 20 sec delay__ 

Relay Driver -  A relay is an electro-magnetic switch which is useful if you want to use a low voltage circuit to switch on and off a light bulb (or anything else) connected to the 220v mains supply.  The diagram below shows a typical relay (with "normally-open" contacts).   __ Designed by David Hoult

Relay driver saves substantial power -  EDN Design Ideas:  July 2, 1998        NOTE:    FILE
has multiple design, scroll for this one.  it is common practice to operate relays and solenoids at a reduced holding power once the mechanical actuation takes place.  Relays are usually specified to pull in within 3 msec at 80% of the rated voltage and to release at 30% of the rated voltage.  The circuit in Figure 1 drives as many as eight 12V (120V coil) power relays, which memory-map into an 8-bit mP bus.  An octal latch stores the relay status, where each bit of the 8-bit word serves a separate relay (0=off, 1=on).  The latch's Select line latches data on the rising edge.  Whenever the relay's status data changes, the relay's drive voltage rises to the full 12V for 140 msec to ensure that the relay pulls in.  A series zener diode then reduces the relay's drive voltage by 50% to reduce dissipation. __ Circuit Design by Tim Herklots, Maxim Integrated Products, Southamption, UK

Relay Driver Switches Two Relays with One Pin -  03/03/11  EDN Design Ideas:  Logic 1, logic 0, and high-Z make for three possible states: forward, reverse, and off. __ Circuit Design by Gunther Kraut, PhD, Egmating, Germany

Relay Driver with Reduced Power -  Relays can handle a lot of power.  However, for certain power sensitive designs you would like to reduce the power needed to hold a relay closed.  The circuit below performs such a task.  it uses a single CD4093 quad NAND gate.  When the on logic input . . . Hobby Circuit designed by David Johnson P.E.-August, 2008

Relay driver, transistorised -  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

Relay logic: Start/Stop buttons -  This is a way of implementing a Start and Stop button system suitable for use with 4QD controllers. __ Designed by Richard Torrens

Relay Toggle Circuit Using a 555 Timer -  This 555 timer circuit below toggles a relay when a button is pressed.  Pins 2 and 6, the threshold and trigger inputs, are held at 1/2 the supply voltage by the two 10K resistors.  When the output is high, the capacitor charges through the 100K resistor, and discharges when the output is low.  When the button is pressed, the capacitor voltage is applied to pins 2 and 6 which causes the output to change to the opposite state __ Designed by Bill Bowden

Relay Toggle Circuit Using a 556 Timer -  This toggle circuit operates by using a couple 555 timers wired as inverters.  Pins 2 and 6 are the threshold and trigger inputs to the first timer and pin 5 is the output.  The output at pin 5 will always be the inverse of the input at pins 2 and 6.  Likewise, the output at pin 9 of the second timer will always be the inverse of the input at pins 8 and 12.  A 100K resistor connects the output of one inverter to the input of the other so the state of one will be the opposite of the other. __ Designed by Bill Bowden

Relay Toggle using a 555 Timer -  This is probably the best toggle circuit.   __ Designed by Bill Bowden

Relay Toggle using a MOSFET  & Push Button -  This circuit is similar to the one above, but uses a N channel mosfet such as iRF530, 540, 640, etc.  in place of the NPN transistor.  Smaller mosfets could be used, but I don't know the part numbers.  I tested the circuit with a iRF640, iRFZ44, iRFZ34 and REP50N06.   The circuit has the same three advantages, it requires only a few parts, always comes up with the relay deactivated, and doesn't need any switch debouncing. __ Designed by Bill Bowden

Relay: Automatic Turn-off -  The above circuits is similar to the "delayed turn-on" type but now configured as an automtic turn-off type.   The diagram shows how the circuit function can be reversed so that the relay turns on when power is applied __ Designed by Tony van Roon  VA3AVR

Relay: Dark Activated -  This circuit switches a relay at dark via a Light Dependent Resistor or LDR for short.  The applications are numerous.  in my application, it switches on a light with an older type movement sensor and is mounted on the top corner of my workshop with the LDR __ Designed by Tony van Roon  VA3AVR

Relay: Delayed Turn-on -  This circuit is a delayed turn-on relay driver and can produce time delays for up to several minutes with reasonable accuracy.  The 14001 (or 4001) CMOS gate here is configured as a simple digital inverter.  its output is fed to the base of a regular 2N3906 (PNP) transistor, Q1, at the junction.   __ Designed by Tony van Roon  VA3AVR

Relay: Long Duration -  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 astable multivibrator which frequency is divided down by IC 2, a 14020 (or 4020) CMOS 14-stage, .   __ Designed by Tony van Roon  VA3AVR

Relay: Long Duration--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

Relay: Self Latching -  This relay driver is Self-Latching which means that once it activates it will remain in that state until S1 is pressed and momentarily disrupts power to the latch __ Designed by Tony van Roon  VA3AVR

Relay: Transistor Boosted -  This relay driver boosts the input impedance with a regular 2N3904 transistor (or equivalent).  Very common driver.  it can drive a variety of relays, including a reed-relay, and is non-latching. 
Transistor Q1 is a simple common-emitter amplifier that increases the effective sensitivity of the 12 volt relay coil about a 100 times.   __ Designed by Tony van Roon  VA3AVR

Relay-12 Sec to 90 min -  Schematic and notes only, no circuit description provided.   __ Designed by Tony van Roon  VA3AVR

Relays & Renewable Energy -  This toggle circuit operates by using a couple 555 timers wired as inverters.  Pins 2 and 6 are the threshold and trigger inputs to the first timer and pin 5 is the output.  The output at pin 5 will always be the inverse of the input at pins 2 and 6.  Likewise, the output at pin 9 of the second timer will always be the inverse of the input at pins 8 and 12.  A 100K resistor connects the output of one inverter to the input of the other so the state of one will be the opposite of the other.   __ Designed by REUK-Renewable Energy UK website

Relays eliminate High-Voltage noise -  09/13/07 EDN Design Ideas:  A simple relay circuit cancels noise in the actuator stage of a scanning electron microscope __ Circuit Design by Jui-I Tsai, Woei-Wu Pai, Feng-Chang Hsu, Po-Jui Chen, Ching-Cheng Teng, and Tai-Shan Liao, National Applied Research Laboratories, Hsinchu, Taiwan

Relays use reverse hysteresis -  05/08/97 EDN Design Ideas:  The relay circuits in Figure 1 take advantage of the disengaging (off) portion of the hysteresis curve (Figure 2).  This standard hysteresis curve comprises two thresholds.  The highest coil-voltage threshold occurs when the relay is inactive and you power the coil.  The lowest threshold occurs when the relay is active and you power off the coil.  First, assume that the relay is in the disengaged position and that you power it with an increasing voltage. __ Circuit Design by Giovanni Romeo, Istituto Nazionale di Geofisica, Roma, Italy

Remote control turns battery on & off -  09/12/97 EDN Design Ideas:  The circuit in Figure 1 acts as a latching solid-state relay.  A short application of a magnetic field in the vicinity of S1 toggles the relay on and off.  The relay switches power from a 3V battery at load currents as high as 10 mA.  This remote switch is ideal for battery-powered applications.  in the off state, the circuit draws no current; in the on state, the circuit draws only 100 A.  All the parts are inexpensive and readily available.    __ Circuit Design by Allen Harstine,Integrated Measurement Systems Inc, Beaverton, OR

Remote Mains Relay Mk.2 -  The PC board used for the USB Sensing Power Switch can also be used to build a remote mains relay.  This can be used for switching mains power to lights or appliances using a remote switch (or relay) linked by low-voltage wiring.  it can also be used for controlling security lights from the relay contacts on a PiR sensor.__ SiliconChip

Remote Relay -  Switch mains voltages safely with this easy-to-build unit__ SiliconChip

Remote Relay Driver -  i received a call from a Discover Circuits visitor who wanted a simple way to turn on an outside lighting system using a low voltage control line.    I suggested the simple circuit below.    The circuit is powered by a 9v battery and uses a very efficient latching relay.    Two low voltage wires lead from the a toggle switch to the remote relay.    A toggle switch selects either the on or off condition of the relay.    The relay contacts are rated at 10 amps, so the small relay can handle a sizeable amount of power.. . . Circuit by Dave Johnson P.E.-April, 2014

Remove Relay-Contact Bounce -  11/27/03  EDN Design Ideas:  Advances in semiconductor technology have allowed ICs  to replace many mechanical relays, but relays still dominate in high-current circuits that must stand off high voltages of arbitrary polarity.  Contact bounce in those relays, ho __ Circuit Design by John Guy, Maxim Integrated Products, Sunnyvale, CA

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