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Relay Circuits, Page 3
Relay Circuits:  #'s - B        C - H        I - O        P - S        T - Z
Last Updated on:
Saturday, August 30, 2014 10:28 AM


Circuits Designed by Dave Johnson, P.E. :
  • 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 contacts closed or unlatch them open.  The 3v powered circuit uses a single 74HC14. This device contains six Schmitt trigger inverters in the one 14 pin package.  Two inverters form a flip/flop circuit.  Each time the pushbutton is pressed, the circuit changes state and stays in that state until the button is pressed again.  With each state change, a 25ms latching or unlatching pulse is produced and is routed to the correct relay coil.  The coil resistance is about 45 ohms so about 70ma of current is drawn from the 3v battery for each relay pulse.  The average power is so low that the circuit can operate for many years on one set of batteries.  I would suggest using two AA or AAA alkaline cells.

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

Inexpensive Relays Form Digital Potentiometer -  03/13/98 EDN-Design Ideas....Build a digitally controlable isolated potentiometer that can tolerate voltages up to 60-Volt dc.... [Design Idea by Robert Perrin, Z-World, Davis, CA]
Infrared Relay with Relay Output -  (electronic circuit added 4/05) [Peter Jakab, Electrical Engineer, Engineer of Informatics]
KD2BD Video Operated Relay -  turns on relay if there is video signal present in the input (added 5/02)
Key-reading circuit saves I/O pins -  6-Mar-03 Issue of EDN  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..... [Design Idea by Gustavo Santaolalla, Digital Precision Systems, Buenos Aires, Argentina]
Latching relay driver -  Schematic only, no circuit description
Latching Relays -  Find out about latching relays and their uses…. [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,....(circuit / schematic design added 6/06)

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Light Activated Relay (Bowden) -  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.... [Circuit Designed by Bill Bowden]
Light Controlled Relay Switch -  Circuit designed by Ron J.  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....(added 09/09/09)
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.…. [Tony van Roon's circuit]
Light/Dark Detector -  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…. [Aaron Cake's design]
Load Sensing Automatic Switch -  apply power to the entire audio system by turning on1-item, simple circuit (added 5/02)
Maximizing the Life Span of Your Relays 5988-6917EN -  Aligent Application Note 1399 (added 4/08)
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....(electronic schematic / circuit added 4/02)
Multiple Relay Drive -  Circuit Ideas for Designers Application Notes Advanced Linear Devices, Inc....[App Note]
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 contacts closed or unlatch them open.  The 3v powered circuit uses a single 74HC14. This device contains six Schmitt trigger inverters in the one 14 pin package.... [Designed by David A. Johnson]
One oscillator drives multiple solid-state relays -  16-Mar-06 Issue of EDN  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.... [Design Idea by Juan Ramón Vadillo Pastor, SOR Internacional SA, Saint Quirze Del Valles, Barcelona, Spain]

Relay Circuits:  #'s - B        C - H        I - O        P - S        T - Z

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