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Latch Circuits
Latch Circuits:  #'s-K      L - 0        P - Z

 

Last Updated: December 31, 2017 06:50 AM

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

Low Voltage Latch CircuitA Discover Circuits visitor wanted a simple on/off latch circuit which can turn on and off power to a small motor.  The kicker was that he wanted to power the circuit and the motor from a single 1.2v NiMH
battery cell.  Texas Instruments comes to the rescue with their family of low voltage single gate ICs.  Specifically the SN74AUP1Q14 Schmitt trigger inverter will operate down to 0.8v and lower.  When used with a good NPN transistor, the circuit below works quite nicely. . . Circuit by David A. Johnson P.E.-March, 2013

Low Voltage Latching Relay DriverUsing 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 Dave Johnson P.E.-August, 2006

On/Off Latch CircuitOften you want to turn on and off power to a device with a single pushbutton switch.  The circuit below performs this logic function with just a few parts and can operate from DC supplies between +3v to about 15v.  It uses two inverters within a 74C14 or a CD4069 hex inverter package.  Each press of the button toggles between the two on/off logic states.. . . Circuit by Dave Johnson P.E.-January, 2010

On/Off Latch Circuit with 2 Second DelayA Discover Circuits visitor needed a latch circuit which could operate using a power supply voltage ranging from 3v to 24v.  He wanted to use a tiny pushbutton switch to turn on and off power to a load.  However, he wanted a 2 second delay between the switch activation and the state change of the output. . . Circuit by David A. Johnson P.E.-June, 2013

On/Off Switch with Latching RelayThe 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 Dave Johnson P.E.-December, 2009


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

Latch -  This circuit is a LATCH and remains ACTIVE when the push-button has been pressed for an INSTANT and released.  __ 555-Timer

Latch Switch -  In this circuit a non-locking push switch is used to activate a load.  The load remains switched on until power is removed from the circuit.   __ Designed by Andy Collison

Latches Solenoid at a Distance -  10/14/00 EDN-Design Ideas The circuit in Figure 1 controls low-cost, latching solenoid valves over long distances.  For example, it can control one valve 1 km away using two wires and a 12V supply.  The circuit provIdeas 700 mA at 12V for the 20 msec necessa __ Circuit Design by J Pelegri and D Ramirez, University of Valencia, Spain

Latching Continuity Tester -  A continuity tester is a must on every service bench for testing cables, pc-boards, switches, motors, plugs, jacks, relays, and many other kinds of components.  But there are times when a simple continuity test  (or your multi-meter) doesn't tell the whole story.  For example, vibration-induced problems in automobile wiring can be extremely difficult to detect because a short or open is not maintained long enough for a non-latching tester to respond __ Designed by Tony van Roon  VA3AVR

Latching Continuity Tester 1 -  This Latching Continuity Tester can help you locate those difficult-to-find intermittent short and opens that other testers always seem to miss.  It has been part of my workbench for many years and performs superb.  I have solved many intermittend problem with this highly flexible unit __ Contact: IQ Technologies

Latching continuity tester using 4093 -  This is a variation on the astable multivibrator.  Circuit was recently developed to test for N-MOSFETs  (the power kind e.g irf830) 

Latching light Detector is frugal with power & parts -  09/26/02 EDN-Design Ideas This idea demonstrates three uses for the humble LED.  The circuit in Figure 1a forms a simple light detector that latches and turns on an LED when the ambient light exceeds a preset limit determined by potentiometer P1.  LED D1 is both the indicator and the light detector.  All junction diodes exhibit some degree of photosensitivity __ Circuit Design by Anthony Smith, Scitech, Biddenham, Bedfordshire, UK

Latching power switch uses Momentary pushbutton -  EDN-Design Ideas 01/20/2014     This could be the cheapest way yet to convert a momentary switch into an on-off power controller __ Circuit Design by Anthony Smith

Latching power switch uses Momentary-action pushbutton -  28-Oct-04 EDN-Design Ideas Most inexpensive pushbutton switches, particularly pc-board-mounting and membrane types, have momentary action.  Latching types are often larger and relatively expensive, and they frequently are unavailable in the style you'd like to use.  You can thus have a problem if you need a small, inexpensive on/off switch for latching power to a load __ Circuit Design by Anthony Smith, Scitech, Biddenham, Bedfordshire, UK

Latching Regulator Prevents Deep Discharge -  03/16/95 EDN-Design Ideas To avoid a deep discharge that can shorten or destroy a rechargeable battery's life, you need to remove the load at the point of complete discharge.  Because a battery's terminal voltage recovers after load removal, you can't simply disconnect the load when the voltage dips below a threshold and reconnect it when the voltage returns above that threshold __ Circuit Design by Doug Vargha, Maxim Integrated Products, Sunnyvale, CA

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

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

Low Voltage Latch Circuit -  A Discover Circuits visitor wanted a simple on/off latch circuit which can turn on and off power to a small motor.  The kicker was that he wanted to power the circuit and the motor from a single 1.2v NiMH
battery cell.  Texas Instruments comes to the rescue with their family of low voltage single gate ICs.  Specifically the SN74AUP1Q14 Schmitt trigger inverter will operate down to 0.8v and lower.  When used with a good NPN transistor, the circuit below works quite nicely. . . Circuit by David A. Johnson P.E.-March, 2013

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 Dave Johnson P.E.-August, 2006

On/Off Latch Circuit -  Often you want to turn on and off power to a device with a single pushbutton switch.  The circuit below performs this logic function with just a few parts and can operate from DC supplies between +3v to about 15v.  It uses two inverters within a 74C14 or a CD4069 hex inverter package.  Each press of the button toggles between the two on/off logic states.. . . Circuit by Dave Johnson P.E.-January, 2010

On/Off Latch Circuit with 2 Second Delay -  A Discover Circuits visitor needed a latch circuit which could operate using a power supply voltage ranging from 3v to 24v.  He wanted to use a tiny pushbutton switch to turn on and off power to a load.  However, he wanted a 2 second delay between the switch activation and the state change of the output. . . Circuit by David A. Johnson P.E.-June, 2013

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 Dave Johnson P.E.-December, 2009

One-button lock provides high security -  03/04/99 EDN-Design Ideas   (contains several designs, scroll to find this one)   Figure 1 is the block diagram of an easily programmed, single-button combination lock.  You operate the lock by using a series of short and long pulses from a momentary switch that masquerades as a doorbell button.  The circuit uses inexpensive CMOS logic.  The retriggerable timer, T1, locks out entries made after the T1 code-entry window, thereby greatly enhancing security.  The circuit in Figure 2 operates as follows: The Schmitt-trigger quad NAND gate, IC1, debounces the code-entry switch and, with the aid of simple analog circuitry, produces separate outputs for activation times of less than and more than 0.3 sec.  These outputs connect to the select gate, IC5 __ Circuit Design by Maxwell Strange, Fulton,MD


Latch Circuits:  #'s-K      L - 0        P - Z


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