• 1.5V LED FLASHER VERSION B
  To squeeze even more energy from a alkaline battery cell, this circuit adds two transistors to a circuit similar to the above design to boost the efficiency. A small 1.5 volt alkaline N cell should flash the LED for a full year. It too uses a "charge pump" technique to provide a LED the needed voltage.

• 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.

• 2 LINE TELEPHONE LINE STATUS INDICATOR
  Many home businesses use multiple phone lines. This circuit gives you a visual indication when a line is in operation. The two AA battery cells should provide enough power for about one year of operation. The circuit is line polarity insensitive.

• 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.

• 3v Low Battery Voltage Flasher
  Many battery powered devices use two AA alkaline cells.  Often you will not know when it is time to replace the batteries until the device powered by them actually stops operating.  The hobby circuit below can be connected to a 3v battery, to give you some warning when the battery is nearing its end of life.  It will flash a LED when the battery voltage drops to about 2.4 volts...

• 9v Battery Voltage Monitor
  Nine voltage batteries are used in a wide variety of electronic devices.  But, you often don’t know when it is time to change the battery until the device stops operating.  The hobby circuit below provides a visual indication when the battery needs to be replaced.  It uses a neat IC from Linear Technology, which contains a very low power voltage reference and a voltage comparator.  The circuit is designed to turn on a LED indicator light when the battery voltage drops below 7.2 volts.

• Audio Signal Detector Switch
  For some audio systems it is desirable to have an automatic switch circuit turn on other devices, such as an amplifier, if an audio signal is detected on one line.  The hobby circuit below will activate a transistor switch when it detects at least 50mv peak to peak of an audio signal.   The switch could be used to turn on a relay, routing the signal to where it is needed.  A single 3v lithium cell will power the electronic circuit for about 5 years.

• CHARGE COUPLED BI-DIRECTIONAL POWER MOSFET RELAY
  The circuit uses an inexpensive C-MOS inverter package and a few small capacitors to drive two power MOS transistors from a 12v to 15v supply. Since the coupling capacitor values used to drive the FETs are small, the leakage current from the power line into the control circuit is a tiny 4uA. Only about 1.5mA of DC is needed to turn on and off 400 watts of AC or DC power to a load.

Dave's Micro Power (Low Power) Circuits: 
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