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Offline Velly  
#1 Posted : Saturday, March 04, 2017 4:14:18 AM(UTC)

Rank: Newbie


Groups: Registered
Joined: 10/25/2016(UTC)
Posts: 2
Location: LA

I'm trying to measure the voltage at a fuel gauge and determine that when the voltage is 3V (representing 1/4 tank) I need a 12V light to go on representing low fuel. Looking at the LM393 on the attached diagram, V+ would be the 12V input from the car battery. I'm unsure how to bring in the input from the fuel guage so when the voltage at the fuel guage drops to the 3V the output of IC 1A goes high. On the attached diagram would I need to connect the fuel gauge voltage at the + input of IC 1A (not requiring R1 and R2 as shown) and then adjust RV to 3V? So in theory when the + input of IC 1A drops to 3V, it matches the input of 3V controlled by RV at the - input of IC 1A which makes the output go high? As far as the 12V light, can I just connect it directly to the output or would I need to consider a transistor & relay configuration? Since LM393 has 4 comparators and I will be using 1 of them, do any of the other comparators need to be tied to voltage as well to prevent "floating" ? thanks!
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