Kitchen Exhaust Fan Controller

Exhaust fan is an
important component in kitchens. Here is a simple circuit to control
kitchen fans by monitoring the ambient temperature. It is built around
the renowned precision integrated temperature sensor chip LM35 (IC1).
Rest of the circuit is a non-traditional electromagnetic relay driver
wired around the popular LED driver LM3914
(IC2). User can switch three presetted temperature levels using a
jumper/slide switch (JP1), which determines the heat level to activate
the relay and hence the electric exhaust fan wired through the relay
contacts. It works off 12V DC power supply.

Kitchen Fan Controller Circuit Schematic

Kitchen Fan Controller Circuit Schematic

Only one adjustment is required in this kitchen exhaust fan
controller circuit. After construction, set jumper point in its first
position, ie base terminal of T1 is connected to pin 13 of IC2 and
adjust the preset P1 carefully so that relay RL1 is energised when
ambient temperature level reaches near 29oC. However this is not very
critical as you can select any threshold level by connecting the jumper
points to other unused output pins of IC2 (here only 3 outputs are

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