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CLOCK CIRCUITS

Circuits designed by David Johnson, P.E.

Last Updated on: Thursday, April 07, 2016 01:02 PM

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2 Transistor Oscillators  -  This page has two unusual two-transistor oscillators.  I set the component values for a low frequency application.  Both circuits draw only about 1 micro Amp of current . . . [Circuit by David Johnson P.E.,  12/14/02]


3 Minute LED Closet Light  -  The circuit below is powered by three 1.5v alkaline AA cells.  With a finger tap to the pushbutton trigger switch, a cluster of 6 wide angle white LEDs is turned on. The lights remain on for about 3 minutes, then will turn off.  The circuitís standby current . . . [Hobby Circuit designed by David Johnson P.E.,  11/14/10]


36-Hour Watchdog Timer  -  A watchdog timer is often used in computer systems to detect when a computer is hung up and is no longer running properly. If it does become locked up and is not able to supply a reset pulse to the circuit within a defined time frame the timer times out a . . . [Circuit by David Johnson P.E.,  04/11/10]

3-Minute Closet Light #2  -  The circuit below is powered by three 1.5v alkaline AA cells.  With a finger tap to the pushbutton trigger switch, a cluster of 6 wide angle white LEDs is turned on. The lights remain on for about 3 minutes, then will turn off.  The circuitís standby current is only a few microamps.  A set of fresh batteries should last at least 200 light applications.  The circuit uses a Schmitt trigger inverter and two transistors.  When the pushbutton switch S1 is pressed, the 10uF capacitor C1 is discharged . . . [Circuit by David Johnson P.E.,  11/14/10]


555 Timer Forms Simple PWM Motor Controller  -  Using a CMOS version of the 555 timer, this circuit can be used to control the speed of a motor by adjusting the duty cycle of the pulses sent to the motor . . . [Circuit by Dave Johnson P.E.,  02/01/07]


60hz Clock Generator is Line Powered  -  This circuit is connected to the 120vac power line and transfers 60Hz clock pulses to a logic circuit. The optoisolator used provides 5000 volts of isolation between the power line and the logic side of the circuit . . . [Hobby Circuit designed by David Johnson P.E.,  02/23/99]


Accurate One Shot Pulse Generator  -  This timer circuit draws only 3ua of current, and can be powered by DC supplies ranging from 3v to 15v.  The circuit produces accurate pulses whose time can easily be adjusted, based on the R1 x C1 time constant.  The time should not change, . . . [Circuit by David Johnson P.E.,  09/02/10]


Automatic Timeout included with this On/Off Flip/flop Circuit  -  This circuit is ideal when a device needs to be turned on and off with a single pushbutton switch, but also needs to turn itself off after some period of time. With the components shown, the output will stay on for only about 20 seconds . . . [Hobby Circuit designed by Dave Johnson P.E.,  05/01/12]


Call-for-Service Beeper  -  This device functions like a lobby desk service request bell.  A short beep is sounded whenever the large pushbutton on top of the device is pressed.  Once pressed, the device will not make another beep until at least 2 minutes of time has elapsed . . . [Hobby Circuit designed by Dave Johnson P.E.,  09/25/05]


Camera Shutter Time Measurement  -  A while back I received an email from someone who needed a simple way to measure the speed of a photographic camera.  I thought about this and suggested the method below.  It relies on an oscilloscope and a cheap photodiode to measure the speed . . . [Hobby Circuit designed by Dave Johnson P.E.,  08/14/11]


Chicken Coop Door Opener with Timer  -  I received an email from a guy in Australia who was trying to build a chicken coop system.  He was planning on using a conventional garage door mechanism to open and close the 6 doors to the coop.  The commercial door opener opened and closed the doors with a single pushbutton.  He wanted to install a standard 220vac powered timer so he could open the doors in the morning and close them at night . . . [Circuit by Dave Johnson P.E.,  03/24/13]


Circuit Forms Divide By 1.5 Counter  -  Two inexpensive ICs divide a TTL clock signal by 1.5. By following the circuit with another flip/flop, you could also generate a divide by three function . . . [Circuit by Dave Johnson P.E.,  07/06/00]


Closet Light with Automatic 3-Minute Timeout  -  The circuit below is powered by three 1.5v alkaline AA cells.  With a finger tap to the pushbutton trigger switch, a cluster of 6 wide angle white LEDs is turned on. The lights remain on for about 3 minutes, then will turn off.  The circuitís standby current is only a few microamps.  A set of fresh batteries should last at least 200 light applications.  The circuit uses a Schmitt trigger inverter and two transistors.  When the pushbutton switch S1 is pressed, the 10uF capacitor C1 is discharged . . . [Circuit by David A. Johnson P.E.,  11/14/10]


Computer, Long Period, Watch Dog Timer  -  This circuit uses a simple 4060 IC oscillator/timer that is reset periodically by a computer. Should the computer fail to send a pulse, the output changes state. The time can easily be set from seconds to hours . . . [Hobby Circuit designed by Dave Johnson P.E.,  01/01/98]


Count Cars with Laser  -  This is an illustration how a laser could be used to count traffic and measure the speed of each car passing through the sensor area . . . [Hobby Circuit designed by David Johnson P.E.,  01/07/07]


Darkroom Camera Shutter Timer  -  This circuit was designed to control a film exposure shutter for a darkroom. It has 8 time steps ranging from 0.35 seconds to 4 seconds. It is activated by a foot switch and draws power from an external 12-volt DC supply . . . [Circuit by David Johnson P.E.,  06/11/00]


Digital Counter Using Pedometer  -  There are many occasions when you may want to count something electronically.  Perhaps it is car traffic on a street or items moving down an assembly line.  It might be the number of times a machine is activated or maybe you want to count the number of . . . [Hobby Circuit designed by David Johnson P.E.,  08/17/08]


Divide a TTL Clock Signal by 1.5  -  Two inexpensive ICs divide a TTL clock signal by 1.5. By following the circuit with another flip/flop, you could also generate a divide by three function . . . [Hobby Circuit designed by David Johnson P.E.,  07/06/00]


Divide By 1.5 Counter  -  Two inexpensive ICs divide a TTL clock signal by 1.5. By following the circuit with another flip/flop, you could also generate a divide by three function . . . [Circuit by David Johnson P.E.,  07/06/00]


Front Desk Service Beeper  -  This device functions like a lobby desk service request bell.  A short beep is sounded whenever the large pushbutton on top of the device is pressed.  Once pressed, the device will not make another beep until at least 2 minutes of time has elapsed . . . [Hobby Circuit designed by David A. Johnson P.E.,  09/25/05]


Garage Door Timer  -  The circuit below is designed to automatically close a garage door, if it was left open for a long period of time.  A reed relay and magnet combination sense when the door is fully open.  An ultra low power voltage comparator oscillator and two 74HC4040 ICs are used to generate the time delay . . . [Circuit by Dave Johnson P.E.,  05/15/11]


Laser Used As Vehicular Traffic Counter  -  This is an illustration how a laser could be used to count traffic and measure the speed of each car passing through the sensor area . . . [Circuit by Dave Johnson P.E.,  01/07/07]


Line Powered 60hz Clock Generator  -  This circuit is connected to the 120vac power line and transfers 60Hz clock pulses to a logic circuit. The optoisolator used provides 5000 volts of isolation between the power line and the logic side of the circuit . . . [Circuit by David A. Johnson P.E.,  02/23/99]


Long Period Computer Watch Dog Timer  -  This circuit uses a simple 4060 IC oscillator/timer that is reset periodically by a computer. Should the computer fail to send a pulse, the output changes state. The time can easily be set from seconds to hours . . . [Circuit by David Johnson P.E.,  01/01/98]


Low Power Oscillators  -  This page has two unusual two-transistor oscillators.  I set the component values for a low frequency application.  Both circuits draw only about 1 microamp of current.Ö [Circuit designed by David A. Johnson P.E., 9/16/07] . . . [Circuit by David A. Johnson P.E.,  12/14/02]


Motorized Duck Decoy Timer  -  I received a nice email from a duck hunter.  He uses some motorized decoys to lure ducks into his line of fire.  However, the battery powered decoys only have an on/off switch so once turned on; the decoy flaps its wings or paddles around continuously.  The hunter wanted a more realistic motion, which would power the motor for say 10 seconds, then stop for another 10 seconds before starting up again. The simple circuit below should work well for his application . . . [Hobby Circuit designed by David Johnson P.E.,  09/04/11]


On/Off Flip/Flop Circuit With Automatic Timeout  -  This circuit is ideal when a device needs to be turned on and off with a single pushbutton switch, but also needs to turn itself off after some period of time. With the components shown, the output will stay on for only about 20 seconds . . . [Circuit by David A. Johnson P.E.,  05/01/12]


On/off Pushbutton Switch with 30 Minute Timeout  -  I received an email from a Discover Circuits visitor.  He wanted to control power to a LED camping light he was building.  He wanted to turn the light on and off with a small pushbutton switch.  He also wanted a timer so the light would not stay on longer than 30 minutes at a time.  It seems that his kids often turned lights on when going to bed and then forgot to turn them off . . . [Circuit by David Johnson P.E.,  01/08/12]


Poor Man's Timer  -  Often during testing of certain equipment and components, you would like to keep track of the elapsed time in hours, minutes and seconds. There are some nice commercial digital timers and counters available for just this sort of application.  However, . . . [Hobby Circuit designed by Dave Johnson P.E.,  08/24/08]


Pushbutton Activates Service Request Beeper  -  A single press of a pushbutton switch turns on a beeper for one second but canít be activated again for 60 seconds. . . . [Circuit by David A. Johnson P.E.,  09/25/05]


PWM Motor Controller uses a 555 Timer  -  Using a CMOS version of the 555 timer, this circuit can be used to control the speed of a motor by adjusting the duty cycle of the pulses sent to the motor . . . [Hobby Circuit designed by David Johnson P.E.,  02/01/07]


Service Request Beeper  -  A single press of a pushbutton switch turns on a beeper for one second but canít be activated again for 60 seconds. . . . [Hobby Circuit designed by David A. Johnson P.E.,  09/25/05]


Three-Minute Closet Light  -  I have a coat closet by my front door.  The thing is very dark at night and really needs some kind of illumination inside.  I could hire an electrician to install a light in the closet ceiling and then wire it to a toggle switch outside the door but that would cost me quite a bit of money . . . [Circuit by Dave Johnson P.E.,  12/25/11]


Timer for Darkroom Camera Shutter  -  This circuit was designed to control a film exposure shutter for a darkroom. It has 8 time steps ranging from 0.35 seconds to 4 seconds. It is activated by a foot switch and draws power from an external 12-volt DC supply . . . [Hobby Circuit designed by David Johnson P.E.,  06/11/00]


Two Transistor Oscillators  -  This page has two unusual two-transistor oscillators.  I set the component values for a low frequency application.  Both circuits draw only about 1 microamp of current.Ö [Circuit designed by David A. Johnson P.E., 9/16/07] . . . [Circuit by David A. Johnson P.E.,  12/14/02]


Two-Transistor Low Power Oscillators  -  This page has two unusual two-transistor oscillators.  I set the component values for a low frequency application.  Both circuits draw only about 1 micro Amp of current . . . [Hobby Circuit designed by Dave Johnson P.E.,  12/14/02]


Watchdog Timer set for 36 Hrs  -  A watchdog timer is often used in computer systems to detect when a computer is hung up and is no longer running properly. If it does become locked up and is not able to supply a reset pulse to the circuit within a defined time frame the timer times out a . . . [Hobby Circuit designed by David Johnson P.E.,  04/11/10]

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