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Circuits designed by David Johnson, P.E.
Last Updated on: Thursday, April 07, 2016 02:04 PM

Master Category List - Dave's Circuits

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Current Loop Circuits

4 to 20ma Current Loop Senses Temperature  -  I designed a circuit similar to this one years ago to accurately measure the air temperature inside a building 1000s of feet from a control room.  The circuit uses a very robust current loop method.  It uses a highly accurate semiconductor temperature sensor . . . [Hobby Circuit designed by Dave Johnson P.E.,  07/04/00]


4-20ma Current Loop Tester  -  This circuit injects an adjustable current through a wire loop.  Using a digital current meter, the current can be adjusted from near zero to over 24 milliamps . . . [Circuit by David Johnson P.E.,  05/01/12]


Monitors Pump Motor  -  This circuit solves this problem in a novel way.  It clips on the outside of the pump motorís power cable and provides a transistor switch closure whenever the circuit detects current flowing to the motor.  The circuit draws so little current that a small lithium cell will power the circuit for years . . . [Circuit Solution by David Johnson P.E.,  11/18/04]

Precision Low Capacitance Meter  -  This circuit was originally designed to measure the volume of fluid inside a medical syringe.  As designed, it produces a zero to 5 volt output, corresponding to a capacitance change of about 10 picofarads . . . [Hobby Circuit designed by David A. Johnson P.E.,  12/12/04]


Pump Motor Monitor  -  This circuit can turn on a light or sound a beeper, whenever an AC line powered pump motor turns on.  It is designed to detect the motor current using a small inductor placed on the outside of the motorís power cable.  No direct wire contact is needed . . . [Circuit by David A. Johnson P.E.,  11/18/04]


Temperature Sensor With 4 to 20ma Current Loop  -  I designed a circuit similar to this one years ago to accurately measure the air temperature inside a building 1000s of feet from a control room.  The circuit uses a very robust current loop method.  It uses a highly accurate semiconductor temperature sensor . . . [Circuit by David Johnson P.E.,  07/04/00]


Tester 4-20ma Current Loop  -  This circuit injects an adjustable current through a wire loop.  Using a digital current meter, the current can be adjusted from near zero to over 24 milliamps . . . [Hobby Circuit designed by Dave Johnson P.E.,  05/01/12]


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