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Humidity sensor

Handy for in the bathroom

Humidity sensor
This circuit was devised by the author to automatically turn on an extraction fan in the bathroom when the humidity becomes too high. The detector circuit consists mainly of a dual CMOS timer, a resistive humidity sensor and a solid-state relay.
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Gerber file

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Component list
R1,R2,R3 = 220kOhm
R4 = 1kOhm
P1 = 100kOhm trimpot, horizontal
C1,C2,C4,C5 = 100nF
C3,C7 = 1000µF 16V radial
C6 = 3.3nF
B1 = B40C1500 bridge rectifier
IC1 = 78L05
IC2 = NE556
IC3 = S101S06V (Sharp) solid-state relay
Tr1 = AC power transformer, PCB mount, sec. 2 x 6V, 350mW (Block type AVB 0,35/2/6)
K1, K2 = 2-way PCB terminal block, lead pitch 7.5mm
K3 = 2-pin pinheader for sensor connection
Sensor: Hygrosens type SHS A2 (Octopart.com)
PCB # 120463-1

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