How to use **741 comparator

[GAZ-52]

Um, good day, pals! Well, I am from Ukraine, so excuse me for my English Hope that you'll understand me.
To cut a long story short - I've faced wit the problem. I've decided to make the "night light", using the charger from the mobile phone (it produces 8,5 Volts DC). I have on old manometer from the truck, and when I rotate the knob of variable resistor, the manometer's needle moves relatively to the dial. The task is to light up the red LED when the voltage at the variable resistor is about 7-6,9 Volts and to turn the LED off when the voltage is 6,9 - 5,7 Volts.
So, I have a UD708 comparator (it's a full soviet analog of **741-series)... And I dunno how to connect it to compare the two signals - the one from the resistor and the second, which is constant (6,9 Volts).
Hope to hear from you soon! I've attached the common circut of my "night light", and it'll be great if you're so kind to draw the circut of comporator connection in my case.
Thanks in advance.
**broken link removed**

 

[pplus]

And how it must work?

 

[GAZ-52]

When the voltage at the variable resistor is between 7-6,9 Volts and it's resistance is high (1170 - 830 Ohms)- the LED has to be on. When I turn the knob and the resistance decreases (829 - 222 Ohms), the voltage is between 6,9 - 5,7 Volts - it's time to turn the LED off. Is it possible to use the comparator in my case?

 

[BradtheRad]

Here is a typical way to operate an op amp in comparator mode.



Since you want the transition to occur at 6.9V, you need to provide a reference. A zener diode can do this.

The potentiometer was dialed to vary the volt level between 5 and 9 V.
The led turns on above 6.9 V.

The 741 output will always be at least 2V above ground level. You can run it on a single supply, but then the led may light dimly when it is supposed to be off. The optional diode will solve this.

 

[GAZ-52]

Yeah, I made it using LM393N comparator.
The scheme:

The green outline stands for the lighting part and the blue outline - for the needle moving and 'red light' part.
It works!

Some photos: