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


Last Updated: November 21, 2017 05:46 AM
Circuits Designed by Dave Johnson, P.E. :

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 David Johnson P.E.-June, 2000

Bidirectional Solid State Relay - The circuit below can switch up to 4 amps of current with a peak voltage up to 20v.  It is fully isolated using two inexpensive red LEDs.  One LED forms a red light source, which illuminates a second red LED.  The circuit takes advantage of the 1.5v. . . Circuit by Dave Johnson P.E.-May, 2009

Computer Controlled Power Relay - Often there is a need to turn on and off a 120vac device using a low power +5v logic signal from a computer.  The circuit below shows how this could be done.  The circuit uses a power relay with a 120vac coil and 10 amp contacts.  A small solid state relay turns on and off the relay.  The solid state relay provides 5KV isolation from the computer . . . Hobby Circuit designed by David Johnson P.E.-July, 2011

Dusk To Dawn Latching Relay -  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. . . . Circuit by David Johnson P.E.-July, 2017

Finger Tap Piezo Relay - 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 9v battery . . . Hobby Circuit designed by David Johnson P.E.-December, 2010

High Temperature Thermocouple activates Relay - Voltage from a high temperature thermocouple activates a relay when the sensor detects a temperature above 1000 degrees F . . . Hobby Circuit designed by David A. Johnson P.E.-July, 2006

High-speed 75MHz 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. . . Circuit by Dave Johnson P.E.-June, 2000

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:

Circuit drives latching relays -  02/01/96 EDN Design Ideas:  Figure 1 shows a low-parts-count circuit that can drive one- or two-coil latching relays.  Latching relays are useful in sensitive analog designs.  The 74ACT174 hex flip-flop has ample capability to drive the Aromat TQ2E series of latching relays.  Both windings for the TQ2E-L2-5V two-coil relay are on the same magnetic element, so the windings' fields add.  You __ Circuit Design by Roy McCammon, 3M Austin, TX

Circuit Removes Relay-Contact Bounce -  27-Nov-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, however, can prove troublesome to downstream circuitry.  One approach to contact bounce combines a relay with a hot-swap controller __ Circuit Design by John Guy, Maxim Integrated Products, Sunnyvale, CA

Circuits Drive Single-Coil Latching Relays -  13-Nov-08 EDN Design Ideas:  Five driver circuits operate single-coil latching relays __ Circuit Design by Alfredo H Saab and Tina Alikahi, Maxim Integrated Products, Sunnyvale, CA

Circuits 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

Clap Relay -  Clap sensitive on-off Relay.3V Battery operated, small portable unit,  __ Contact Flavio Dellepiane, fladello @ tin.it

CMOS Latches Relays -  11/18/10 EDN Design Ideas:  A driver circuit take pulses and sets relays.  [Design ideas - by JC Maillet, Gabriola island, BC Canada __ Circuit Design by JC Maillet, Gabriola Island, BC Canada

CMOS Toggle Flip Flop using Push Button -  The circuit below uses a CMOS dual D flip flop (CD4013) to toggle a relay or other load with a momentary push button.  Several push buttons can be wired in parallel to control the relay from multiple locations.  A high level from the push button is coupled to the set line through a small (0.1uF) capacitor.  The high level from the Q output __ Designed by Bill Bowden

Computer Controlled Power Relay -  Often there is a need to turn on and off a 120vac device using a low power +5v logic signal from a computer.  The circuit below shows how this could be done.  The circuit uses a power relay with a 120vac coil and 10 amp contacts.  A small solid state relay turns on and off the relay.  The solid state relay provides 5KV isolation from the computer . . . Hobby Circuit designed by David Johnson P.E.-July, 2011

Controlling Relays with Logic Voltages -  The schematic below illustrates 4 methods of controlling a relay with a digital logic signal.  Figure (A) can probably be used in most cases where the relay coil requires 100 mA or less and the input current is 2 milliamps or more.  The resistor value (R) is determined from the input voltage and the available current.  For example, a 5 volt input signal supplying 2 milliamps would require (5-.7) /.002 = 2150 ohms, or a 2.2K standard value.   __ Designed by Bill Bowden

Countdown timer with Relay -  Timing and oscillator circuit diagrams / circuit schematics__ Carl's Electronics

Dancing LEDs -  LED sequencer: follows the rhythm of music or speech; 9V Battery-operated portable unit __ Contact Flavio Dellepiane, fladello @ tin.it

Dark Activated Relay -  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

Dark/Light 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

Delayed Turn-On Relay -  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

Digital Impulse Relay -  in the first place, a relay is like a switch to a coil assembly.  This switch is activated when electricity is applied to the coil.  With a common relay, the electricity must be continuously applied to the coil to __ Designed by Magirescu Iulian

Drive latching relays -  02/01/96 EDN Design Ideas:  Figure 1 shows a low-parts-count circuit that can drive one- or two-coil latching relays.  Latching relays are useful in sensitive analog designs.  The 74ACT174 hex flip-flop has ample capability to drive the Aromat TQ2E series of latching relays.  Both windings for the TQ2E-L2-5V two-coil relay are on the same magnetic element, so the windings' fields add.  You __ Circuit Design by Roy McCammon, 3M Austin, TX

Drive Single-Coil Latching Relays -  11/13/08  EDN Design Ideas:  Five driver circuits operate single-coil latching relays __ Circuit Design by Alfredo H Saab and Tina Alikahi, Maxim Integrated Products, Sunnyvale, CA

Drive two relays via one wire -  This is a very simple circuit which will drive either of two relays via one wire.  Apply supply voltage to the control wire and one relay operates.  Apply zero volts to the wire and the other relay operates.   __ Designed by Richard Torrens

Dual Relay Driver Board -  We have used two Goodsky RWH-SH-112D 12V relays, coil resistance 400 ohm.  it is rated to switch 250VAC at 12A.  However, because of the PCB track thickness and width we do not recommend using the
relay to switch more than 5A.  if you.   __ Contact IQ Technologies

Dual-Coil Relay Driver Uses Only Two MOSFETs -  22-Oct-09 EDN Design Ideas:  Differentially drive relays to minimize power consumption __ Circuit Design by Mehmet Efe Ozbek, PhD, Atilim University, Ankara, Turkey

Dusk To Dawn Latching Relay -  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. . . . Circuit by David Johnson P.E.-July, 2017

Electronic Breaker -  This circuit uses the on-resistance of the MOSFET as the current sensor.  Reset it by removing the input power or the load.  The circuit draws no current unless tripped.   __ Designed by Andrew R. Morris

Electronic Relay Latching -  i've spent a lot of time thinking about how I want to wire my conversion.  The electrical system will consist of a combination of 12 volt DC, 24 volt DC, and 110 volt AC.  it's important that the system provide the greatest functionality, but have a simple interface.  it must be easy to install and relatively inexpensive to build.  The system can't be overly complicated and must be easy to maintain.   __ Designed by 2001-2010 Craig Shepard

Electronic Thermostat Relay -  Here is a simple thermostat circuit that can be used to control a relay and supply power to a small space heater through the relay contacts.  The relay contacts should be rated above the current requirements for the heater.  Temperature changes are detected by a (1.7KAT70F) thermistor placed in series with a 5K potentiometer which produces about __ Designed by Bill Bowden

Electronic Toggle Switch No.1 -  Switching Circuits:  This simple circuit will energize and de-energize a relay at the push of a button.  Pushing the button once - will energize the relay.  And pushing it a second time - will de-energize the relay.  The accompanying Circuit Description offers a good introduction to the workings of the CMOS 4013. __ Designed by Ron J.

Electronic Toggle Switch No.2 -  Switching Circuits:  This is similar to the first circuit - but it is based on the CMOS 4017.  Pushing the button once - will energize the relay.  And pushing it a second time - will de-energize the relay.  The accompanying Circuit Description offers a good introduction to the workings of the 4017.  __ Designed by Ron J.

Electronic Toggle Switch No.3 -  Switching Circuits:  This circuit can be used as two entirely separate toggle switches - with each push button successively energizing and de-energizing its own relay.  Or the two switches can be interlinked with diodes - to produce a number of different switching patterns.  For example - they can be used to reverse the direction of DC motors.  __ Designed by Ron J.

Finger Tap Piezo Relay -  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 9v battery . . . Hobby Circuit designed by David Johnson P.E.-December, 2010

Forcible latch module -  This is set-reset latch: it is a 'personality module for 4QD-TEC transistorised relay system.  However it is an R-S latch with a difference in that it can be set by a High or a Low signal (as appropriate) on either input.  The latch can be forced eithr way, and stays that way until next changed.   __ Designed by Richard Torrens

Generating a Delayed Pulse with a Dual 555 Timer -  The circuit below illustrates generating a single positive pulse which is delayed relative to the trigger input time.  The circuit is similar to the one above but employs two stages so that both the pulse width and delay can be controlled.  When the button is depressed, the output of the first ( __ Designed by Bill Bowden

High efficiency, legal limit, solid state linear HF Amplifiers -  Not a project yet, but very theoretical thoughts about very practical amplifiers!  __ Designed by Manfred Mornhinweg

High Temperature Thermocouple activates Relay -  Voltage from a high temperature thermocouple activates a relay when the sensor detects a temperature above 1000 degrees F . . . Hobby Circuit designed by David A. Johnson P.E.-July, 2006

High-speed 75MHz 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. . . Circuit by Dave Johnson P.E.-June, 2000

Hybrid vacuum tube/solid-state audio power Amplifier -  08/11/14  EDN Design Ideas:  An audio power amp design that combines vacuum tube input circuitry with solid-state output and feedback components. __ Circuit Design by Craig D. Merz

Impulse Changeover Switch -  So what on earth is an 'impulse changeover switch'? Easy - a switch which changes state each time it gets an impulse.  You may think it's just a fancy name for a bistable - OK I admit it.  However in the welding industry we used to use an 'impulse changeover relay' to control the direction of a d.  c.  motor used to oscillate a welding head between mechanical end stops.  There was a roller-lever operated microswitch and two adjustable position blocks.  Each time the microswitch hit a block, the relay changed over.  How crude can you get?  __ Designed by Richard Torrens

Inexpensive Relays Form Digital Potentiometer -  03/13/98 EDN Design Ideas:  NOTE:  File contains many circuits, please scroll to find this one.  Build a digitally controlable isolated potentiometer that can tolerate voltages up to 60-Volt dc __ Circuit Design by Robert Perrin, Z-World, Davis, CA

Infrared Relay with Relay Output -  infrared remote controls are using a 32-56 kHz modulated square wave for communication.  These circuits are used to transmit a 1-4 kHz digital signal (OOK modulation) through infra light (this is the maximum attainable speed, 1000-4000 bits per sec).  The transmitter oscillator runs with adjustable frequency in the 32-56kHz range, and is being turned ON/OFF with the modulating signal, a TTL voltage on the MOD input.  On the receiver side a photodiode takes up the signal.  The integrated circuit inside the chip is sensitive only around a specified frequency in the 32-56 kHz range.  The output is the demodulated digital input (but usually inverted) , just what we used to drive the transmitter.  When the carrier is present, this output is usually low.  When no carrier is detected, the output is usually high.   __ Designed by Peter Jakab

KD2BD Video Operated Relay -  turns on relay if there is video signal present in the input__ 

Key-Reading Saves I/O Pins -  6-Mar-03 EDN Design Ideas:  Amplifiers perform precision divide-by-2 circuit - Some microcontroller applications usually use too many i/O pins to read keys or onboard switches; in many cases, few pins remain available for other uses.  Some alternative ways to read keys yieldfree pins.  First, consider some ways to effect key reading.  Table 1 presents a comparison of four methods with references to circuit configurations (figures 1, 2, 3, and 4] __ Circuit Design by Gustavo Santaolalla, Digital Precision Systems, Buenos Aires, Argentina

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


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