Circuit Project Electronic

Detects the amount of salt contained in liquid foods
Three-level LED indicator

This circuit was designed to detect the approximate percentage of salt contained in a liquid. After careful setting it can be useful to persons needing a quick, rough indication of the salt content in liquid foods for diet purposes etc.
IC1A op-amp is wired as a DC differential amplifier and its output voltage increases as the DC resistance measured across the probes decreases. In fact, fresh water has a relatively high DC resistance value that will decrease proportionally as an increasing amount of salt is added.
IC1B, IC1C and IC1D are wired as comparators and drive D5, D4 and D3 in turn, as the voltage at their inverting inputs increases. Therefore, no LED will be on when the salt content of the liquid under test is very low, yellow LED D5 will illuminate when the salt content is low, green LED D4 will illuminate if the salt content is normal and red LED D3 will illuminate if the salt content is high.

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Parts:

R1________________470R 1/4W Resistor
R2,R5______________10K 1/4W Resistors
R3,R6_____________220K 1/4W Resistors
R4__________________5K 1/2W Trimmer Cermet
R7________________680R 1/4W Resistor
R8__________________2K2 1/4W Resistor
R9,R10,R11,R12,R13__1K 1/4W Resistors

C1________________100µF 25V Electrolytic Capacitor

D1,D2,D3______3 or 5mm. Red LEDs
D4____________3 or 5mm. Green LED
D5____________3 or 5mm. Yellow LED

IC1_______________LM324 Low Power Quad Op-amp

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Thank you.