Here is a simple circuit “Fridge Alert System” can be used in fridge, indicating whether the temperature is more than pre-defined temperature. The arrangement of the circuit fridge alert system showed here alert when temperature increased then 5⁰C.

Thermistor TH₁ is used as temperature sensor, change their resistance whenever changes in surrounding temperature. IC₁ CL7611 combined with thermistor to complete all the process of temperature. IC₂ is used here to indicate the status of battery. Glowing LED₁ indicate temperature is more than 5⁰C.

PARTS LIST

Resistors (all ¼-watt, ± 5% Carbon)

R₁, R₂ = 4.7 MΩ

R₃ = 2.2 MΩ

R₄ = 56 KΩ

R₅ = 12 KΩ

R₆ = 10 KΩ

R₇ = 270 Ω

R₈ = 390 Ω

Semiconductors

IC₁ = CL7611

IC₂ = 8211

T₁ = 2TX300

LED₁ = RED

LED₂ = Green

Miscellaneous

SW₁ = Push-to-on switch

TH₁ = GL16 thermistor