• 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.

• 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....

• 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....

• 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....

• 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. 

• 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....

• 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….

Bistable Multivibrator Circuits

Master Category List - Dave's Circuits