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1.5v Touch Activated Switch - A single 1.5v silver oxide button cell powers this complete touch activated switch circuit for 5 years.  It features both a normally open and a normally closed set of solid-state switch thermals.  It also has an adjustable sensitivity, which can be set for a touch capacitance change as small as 1 picofarad.
12F675 as a Flip Flop - Code to make a 12F675 operate as a D-type or JK-type flip flop.  Since I implemented a D type flip flop using  PIC Logic Elements I thought I might go  or way and implement an entire D type flip flop in a single PIC.  This uses  edge triggered and port change status interrupts and was an opportunity to have a play with interrupts on  PIC.
3v Capacitance Proximity Switch - This circuit was designed to provide a touch activated switch function without an external power supply.  It draws so little power that a single 3v battery will operate the circuit for many years.  It is discussed in more detail in the section on Capacitance Proximity Switch Technology. (Note: link is off-site)
555 Bistable Circuit - Basic circuits and information about this timer/oscillator.  Scroll to find Bistable Circuit
An SCR Flipflop  for Alternating Flashing Light Bulbs
AN-1150: COP8 FLASH ISP HANDBOOK-Intro to ISP - National Semiconductor Application Note
AN-1281:Bumped Die Flip Chip Packages - National Semiconductor Application Note
CMOS Toggle Flip Flop using Laser Pointer - 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 is inverted by the upper transistor and supplies a low reset level to the reset line for about 400 mS, after which time the reset line returns to a high state and resets the flip flop.
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..
DAC & flip flops form constant current source - 04/23/09 EDN- Design Ideas,  Using two flip flops, you can program a serial-input DAC to produce a constant 4 mA..
Descrete Set/Reset Flip Flop - Here are two examples of bistable flip flops which can be toggled between states with a single push button. When the button is pressed, the capacitor connected to the base of the conducting transistor will charge to a slightly higher voltage. When the button is released, the same capacitor will discharge back to the previous voltage causing the transistor to turn off. The rising voltage at the collector of the transistor that is turning off causes the opposite transistor to turn on and the circuit remains in a stable state until..
D-Flip/Flop One Shot Circuit - Yes you can use cheap D flip/flop logic circuits as nice one-shot pulse generators. This schematic shows how the popular CD4013 and the CD74HC74 can be used to generate pulses ranging from nanoseconds to seconds.
D-Flip/Flop Oscillators - Yes you can turn flip/flop ICs into low current oscillators. This schematic shows you how.
Discrete BiStable Flip Flop
Discrete Set/Reset Flip Flop - This is an example of a set/reset flip flop using discrete components. When power is applied, only one of the transistors will conduct causing the other to remain off. The conducting transistor can be turned off by grounding it's base through the push button which causes the collector voltage to rise and turn on the opposite transistor.
Dual flip flop forms simple delayed pulse generator - EDN-Design Ideas: A delayed pulse generator provides precision timing adjustments..
Electronic circuit replaces mechanical push push switch - EDN-Design Ideas: Toggle-action circuit uses a low-cost momentary-contact switch..
Flashing LED Advertising Badge #1 - I have seen numerous flashing light badges at trade shows and conventions. They are often handed out as gifts to promote some business. The devices often use inefficient circuits, which cause the battery power source to be quickly depleted. My circuit is simple but efficient enough to provide months of continuous LED flashing. It also has a tiny push-button switch to turn on and off the light flashing, extending battery power.
Flashing LED Advertising Badge #2 - This circuit is similar to flashing LED advertising badge #1.  .  It uses a CD4013 dual D Flip/Flop IC.  The 74HCT74 IC in #81 does not always work.  As in #81, a single lithium battery will provide months of continuous LED flashing.  It also has a tiny push-button switch to turn on and off the light flashing.
Flip Flop Circuit - In this project we examine one of the most valuable circuits to be invented, the flip flop. Originally it was designed with VALVES, along with its simpler version (without the two capacitors, called a bi-stable Multivibrator), it was realised it.
Flip Flop Flashers Buzzers Etc - Several circuits here.  The familiar astable flip-flop circuit is a handy configuration for making flashers or generating squarewaves. Here is a typical alternating LED flasher with the LEDs in the emitters instead of collectors as is normally done. The bias resistors are directly connected..
Follow the Debouncing Flip Flops - EDN-Design Ideas
FPGA Circuit Emulates 74x74 Flip Flop - EDN-Design Ideas
FPGA implements X.50 Division 3 recommendation - EDN-Design Ideas: The scheme in Figure 1a uses five delay cells and an XOR gate to configure the data stream for the X.50 Division 3 recommendation of ITU-T. The X.50 recommendation defines the fundamental parameters of a multiplexing scheme for inter working data 
Gated Oscillator Emulates a Flip Flop - EDN-Design Ideas
High Current MOSFET  Flip Flop with Debounced Pushbutton - This circuit was adapted from the "Toggle Switch Debounced Pushbutton" by John Lundgren. It is particularly useful in controlling a load from several locations where the load may be switched on from one location and switched off from another. Any number of momentary (N/O) switches or push buttons may be connected in parallel.
Honeybee Counter - I designed a circuit similar to this one a long time ago to help a beekeeper count the number of bees going into or out of a hive. The low power circuit uses a slotted opto-sensor to detect the passing bees. The circuit advances an electronic counting module whenever a honeybee passes through the sensor. The device only counts the number of bees going through the sensor. A different circuit would be needed to count the number of bees only going out or only coming into the hive.
Miniature Pushbutton On/Off Switch - In many battery powered devices, you would like to turn the circuit on and off by pressing a small pushbutton switch.  One press turns the device on and second press turns it back off.  The flip/flop circuit below uses a minimum number of parts to perform this function.  It operates from DC supply voltage which can range from 2v to 6v.  It draws very little current and takes up little space.  Yet, it can control up to one amp of current.  The circuit uses a single flip/flop device made by Texas Instruments. 
Monostable Flip Flops One Shot
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.
Pushbutton Oneshot & Latch - This circuit uses a single IC to convert a noisy pushbutton switch signal into a clean pulse or a sustained push on-push off signal. It can operate from 3v to 18v.
SCR Flipflop  for Alternating Flashing Light Bulbs
Set/Reset Flip Flop
Soft On/Off Switch - This project describes how to build a "soft touch" switch. By "soft touch" we mean that you have to push once to set device ON and push again to set device OFF. This kind of switch works by latching a relay to ON state with push of a button and with another push latch is released. It is working like flip-flop states. In that way you can control power to a device using one push button
Sound Controlled Flip Flop - Described here is a very inexpensive solution to many phono-controlled applications like remote switching on, for instance, or activating a camera, tape recorder, burglar alarms, toys, etc. The circuit given here employs a condenser microphone as the pick-up. A two-stage amplifier built around a quad op-amp IC LM324 offers a good gain to enable sound pick-up upto four metres.
Spare flip flop stretches WR strobe for DSP - EDN-Design Ideas
Spare gates form edge triggered flip flop - EDN-Design Ideas
Telephone Line Based Audio Muting & Light on Circuit
Telephone Line Based Audio Muting & Light-On Circuit
Time to Dust Indicator - I thought about this circuit when I heard that a lot cleaning personal in hotels were either dusting rooms more often than necessary or not enough. I have not yet built and tested this circuit completely but in concept it should work. The circuit draws very low current from a +3v battery and could be housed in a package similar to a small ashtray. The assembly might be placed in a suitable out of the way area to collect dust. It would alert a maid when it was time to dust the room. The circuit detects dust with an infrared LED that is pulsed so its light shines onto a smooth flat plate. Any dust settling onto the surface is detected by a phototransistor, mounted at a 90-degree angle from the LED. When the dust reaches a particular level, sufficient light is reflected into the phototransistor to change the logic state of the circuit to an alarm condition. The alarm output could be connected to a beeper, a flashing LED or to one of the LED flashing circuits in this hobby circuit section.
Verilog Program Models metastable flip flop - EDN-Design Ideas
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