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Relay Circuits, Page 1
Relays:  #'s - B        C - H        I - O        P - S        T - Z
Last Updated on:
Thursday, October 30, 2014 09:22 AM


Circuits Designed by Dave Johnson, P.E. :
  • 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 produced by super bright red LEDs when illuminated with red light.  The voltage produced by one red is routed to two n-channel FETs, configured in a bi-directional switch circuit.  The two FETs selected have a low gate-source threshold voltage, which allows them to turn on hard from the 1.5v from the red LED.  The bi-directional configuration allows the circuit to switch both AC and DC power.  Using quality super bright red LEDs, the circuit will switch on fully with only 5ma of LED current.


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

1 min to 20 hrs Long Duration Relay -  Shows a 'long-range timer relay' switching circuit which spans 1 minute to 20 hours in three ranges using a three-step, two-deck mechanical rotary switch… [Tony van Roon's electronic schematic]
1 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]
12 Sec to 90 min Relay -  Schematic and notes only, no circuit description provided…. [Tony van Roon's circuit]
122 Volt AC Lamp Chaser using Solid State Relays -  This circuit is similar to  LED clock using12 neon indicator lamps instead of LEDs. It operates from2 high capacity ni-cad cells (2.5 volts) which keep it going for a couple weeks. High voltage (70 volts) for  neon lamps is obtained from a small....(added 4/02)
4 channel infrared remote relays -  …. [Site is under construction right now]
555 Timer MonoStable Circuit using Pushbutton -  The two circuits above illustrate using the 555 timer to close a relay for a predetermined amount of time by pressing a momentary N/O push button. The circuit on the left can be used for long time periods where the push button can be pressed and released before the end of the timing period. For shorter periods, a capacitor can be used to isolate the switch.... [Bill Bowden's website]
60 Watt RF Amplifier -  Soild state RF power amplifier using IRF840. Simple and easy to construct. IRF840 can handle a maximum power output of 125 Watts.
741 Based Light Sensor -  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]
8 Channel LPT relay board -  Channel Relay Board is a simple and convenient way to interface 8 relays for switching application in your project…..
9 Second Digital Readout Countdown 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,… [Bill Bowden]
9 Second 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,… [Bill Bowden]
AC Line Current Detector -  This circuit will detect AC line currents of about 250 mA or more without making any electrical connections to the line. Current is detected by passing one of the AC lines through an inductive pickup (L1) made with a 1 inch diameter U-bolt wound with 100% turns of #30, #35 magnet wire. The pickup could be made from other iron type rings or.... [Bill Bowden]
Alternating on/Off Control -  This circuit uses three easily available 555 timer ICs. All three work as astable multivibrators. The first 555 has an on period and off period equal to 1 sec.  This IC controls  on/ off periods of  or 2 555s which are used to flash two bulbs through  relay contacts.... [Tony van Roon's circuit]
Analog switch lowers relay power consumption -  20-Dec-01 Issue of EDN  Designers often use relays as electrically controlled switches. Unlike transistors, their switch contacts are electrically isolated from the control input. However, the power dissipation in a relay coil may render the device unattractive in battery-powered applications. You can lower this dissipation by adding an analog switch that allows the relay to operate at a lower voltage (Figure 1].... [Design Idea by Steve Caldwell, Maxim Integrated Products, Chandler, AZ]
Assorted relay Control circuits -  several circuits here, spend some time and view each of them
Basic Solid State Relays -  These Relays would be ideal for applications where many relays are needed and the load current requirements are low. Due to their small size a large number of relays could be mounted on a single printed circuit board.  The relays are based on a 4N33 Optoisolator package.  This device has a Darlington.... [from Rob Paisley's Model Train web site]
Basic Stamp I & PC Relay Controller -  This project shows you how to build a relay controller using the Basic Stamp I interfaced to the PC serial port.  The Visual Basic 5 software developed for the interface lets you interact with the Basic Stamp to turn ON/OFF up to (2) relays attached to the Basic Stamp I/O pins.  As shown below in the screen capture of PC-Relay, it's easy to select the desired com port using the drop-down menu....(electronic circuit added 4/05)
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 produced by super bright red LEDs when illuminated with red light.  The voltage produced by one red is routed to two n-channel FETs, configured in a bi-directional switch circuit.  The two FETs selected have a low gate-source threshold voltage, which allows them to turn on hard from the 1.5v from the red LED.  The bi-directional configuration allows the circuit to switch both AC and DC power.  Using quality super bright red LEDs, the circuit will switch on fully with only 5ma of LED current. [Designed by David A. Johnson]

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


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