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Circuits > Security and other sensors and detectors > Dew sensor
Dew sensor
Dew (condensed moisture) ad- versely affects the normal per- formance of
sensitive electronic devices. A low-cost circuit described here can be used to
switch off any gadget automatically in case of excessive humidity. At the heart
of the circuit is an inexpensive (resistor type) dew sensor element. Although
dew sensor elements are widely used in video cassette players and recorders,
these may not be easily available in local market. However, the same can be
procured from authorised service centres of reputed companies. The author used
the dew sensor for FUNAI VCP model No. V.I.P. 3000A (Part No: 6808-08-04,
reference no. 336) in his prototype. In practice, it is observed that all dew
sensors available for video application possess the same electrical
characteristics irrespective of their physical shape/size, and hence are
interchangeable and can be used in this project. The circuit is basically a
switching type circuit made with the help of a popular dual op-amp IC LM358N
which is configured here as a comparator. (Note that only one half of the IC is
used here.) Under normal conditions, resistance of the dew sensor is low (1
kilo-ohm or so) and thus the voltage at its non-inverting terminal (pin 3) is
low compared to that at its inverting input (pin 2) terminal. The corresponding
output of the comparator (at pin 1) is accordingly low and thus nothing happens
in the circuit. When humidity exceeds 80 per cent, the sensor resistance
increases rapidly. As a result, the non-inverting pin becomes more positive than
the inverting pin. This pushes up the output of IC1 to a high level. As a
consequence, the LED inside the opto-coupler is energised. At the same time LED1
provides a visual indication. The opto-coupler can be suitably interfaced to any
electronic device for switching purpose. Circuit comprising diode D2, resistors
R5 and R6 and capacitor C1 forms a low-voltage, low-current power supply unit.
This simple arrangement obviates the requirement for a bulky and expensive step-down
transformer.
Title: Dew sensor
Source: www.electronic-circuits-diagrams.com
Published on: 2005-02-09
Reads: 735
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Circuits > Security and other sensors and detectors > Dew sensor |
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