temperature indicator can be designed using electronic circuit diagram
below. Temperature indicator consists of two special zener diode, D1 and
D2, connected in series to ensure accuracy of 5.96 V Zener voltage at
25 ° C. As long as the radiator temperature does not exceed 50 ° C,
thermal indicator will flash a green LED, one orange will be provided for temperatures of 50 … 75 ° C and a red LED, for temperatures above 75 ° C.
Zener voltage will increase by 20 mV for each temperature increase
of a degree Celsius temperature. Radiator temperature corresponding
voltage level is compared with two reference voltages, IC1 and IC2
using. When the temperature reaches 50 ° C, IC2’s output goes to logic
state “1” so that T3 leads and following ignition with diode D4. At 75 °
C, IC1’s output is in logic state “1” and, therefore, T2 and T3 will,
so that D3 and D4 lights are off.