# Trying to make a notifying system using a thermistor

Joined Dec 29, 2023
3
I am making a temperature sensor, which illuminates three LEDs (green, yellow, and red). The green LED is intended to be illuminated initially, followed by the yellow and red LEDs. In constructing this circuit, I employed a bargraph voltmeter. However, I have a problem with the mathematical aspects as the LEDs activate at a low temperature (I want the red LED to turn on when the temperature is 60 degrees, but it activates at 10).

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#### crutschow

Joined Mar 14, 2008
34,842
What is the resistance of the thermistor at 60 degrees (Celsius)?
At what temperature do you want the other LEDs to light and what is the thermistor resistance at those temperatures.

Joined Dec 29, 2023
3
What is the resistance of the thermistor at 60 degrees (Celsius)?
24.43k ohms

#### MrChips

Joined Oct 2, 2009
31,082

Black is not my favorite colour for background. White is prefered.

You are using an analog comparator that compares one input with another.
One input threshold level is set by voltage dividers.
How is the temperature input voltage determined? Don't you need a voltage divider there also?

Is this homework?

Joined Dec 29, 2023
3
No, more like a personal project. The input voltage is from a generator and I may need to convert ac to dc but I will focus on that problem later. Why do I need a voltage divider?

#### MrChips

Joined Oct 2, 2009
31,082
As wired, R1 transmits a current. The analog comparator IC needs voltage input.
Try putting a pull down resistor to create a voltage divider.