Hi everyone, I am new here. Just wonder if anyone know how to design a DC voltage indicator using dual colour or ideally even triple colour LED, so it is function as follow:

Vout<11V red
{11V<Vout<12.5V orange}
Vout>12.5V Green

And anyway to make the reference adjustable.

Thanks.

 

Hello,

You will need two comparators.
One that switches the red off above 12.5 Volts and
one that switches the green off below 11 Volts.

Greetings,
Bertus

 

Erm............ I thought using comparators need a reference voltage. But in this case, it is to indicate the battery voltage level and there won't be an other power supply. How could the circuit designed to "know" the reference voltage?

 

Hello,

A comparator needs a reference.
This can be a zenerdiode for instance.
The other input will be the measure input.
Depending on the inputs the comparator will switch on or off.

Take a look at this page of the AAC eBook.
http://www.allaboutcircuits.com/vol_3/chpt_8/3.html

Greetings,
Bertus

 

Use an LM3914 bar-graph LED driver IC. It has 10 comparators (use only 3 if you want) and an adjustable regulated reference voltage.