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Circuits designed by David Johnson, P.E.
Last Updated on: Monday, July 11, 2016 01:59 PM

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Temperature Circuits

  • Freezing Temperature Alarm
    This circuit turns on a beeper whenever the outside air temperature is less than zero degrees Centigrade.  The circuit draws only a few microamps from a 9 volt battery.  It uses a glass bead thermistor accurate to 1 degree C.
  • Freezer Over-Temperature Alarm
    This electronic hobby circuit below is designed to activate a beeper alarm, whenever the outside air temperature is below 0 degrees C (32F).  A 9v battery powers the hobby circuit.  The average 9ua current is so low that the battery should last for many years....

  • MICRO POWER OVER-TEMPERATURE ALARM
    The circuit is powered for years by a single 3 volt lithium battery. It sounds an alarm when the temperature exceeds a certain point. With some minor changes the circuit could also be configured for an under temperature (freeze) alarm. The circuit uses a cheap but accurate thermistor as the temperature sensor.

More  Temperature Circuits
 

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The circuits on this site are designed by David A Johnson - unless otherwise noted.  David A. Johnson & Associates.  All Rights reserved. 
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