Hi everyone...i have this project of water level detector. Im planning to add a feature which is...the LED level indicator will change color when cold/hot water is in the water tank. I want the LED to light ups in blue for cold water and light ups red for hot water.

I have been searching the circuit for the temperature dependence LED but still not found any.

Can anyone give ideas on how to achieve the intended feature? any circuit reference available?

Any supportive comments are welcome. Thanks

 

I have never seen such thing as temperature dependant LED, as I see it, the fast way to achieve this is use a low pin count MCU and a temp. sensor sucha as LM35 or the digital DS12XX, write the apropriate code for this and voila!!! If you take such endeavor, many people here would be willing to help, but please be super specific with you requirements

 

You will need to use two LEDs, one red and one blue, or a red/blue bicolor LED.

 

Like Felo said a pic makes everything just a matter of programming.

But for people like me w/ zero knowledge of programming a analog solution may be more appropriate.

If it where me, i would use a op amp as comparator and have the output drive the gates of a pnp/npn mosfet.

This is a ghetto way of doing it,but works ......

Perhaps someone else will suggest a better way that don't involve coding.

-luvv-

 

First, pick your sensor. Then pick your range.

Then you need to design an analog circuit that does what you want with voltage swing.