IC1 acts as a arch detector and amplifier: its achievement voltage raises back temperature increases and vice-versa. This happens because the n.t.c. resistor R2 reduces its attrition amount as temperature increases and vice-versa, accordingly unbalancing the arch formed by R1, R2, R4, R5. IC2A and IC2B anatomy a window comparator and R8 is the acuteness control.
Before starting a altitude the ambit charge be counterbalanced by agency of R1 in adjustment to access that both LEDs are off. If R8 is set to aught attrition the ambit acuteness will be at best and one of the LEDs will brighten back a actual slight aberration in temperature will be detected. As R8 amount is added the ambit acuteness will decrease.
Portable Detector Comparator Temperature Part List
R1 = 22K Linear Potentiometer
R2 = 15K @ 20°C n.t.c. Thermistor
R3 = 10K
R4,R5,R7,R9 = 22K
R6 = 220K
R8 = 5K
R10 = 680R
C1 = 47µF
D1 = Red LED
D2 = Green LED
IC1 = TL061 Low current BIFET Op-Amp
IC2 = LM393 Dual Voltage Comparator IC
P1 = SPST Pushbutton
B1 = 9V
