I made this voltage indicator for my homemade psu(10 v). But the problem is all light goes off under 8 volt. How to make that at least one light is on at 2-3 volt.

 

All your leds are in series, so will need approx 10 volts minimum to make them all light, better to use a TL431 zener on one led set to say 2.5/ 3V, with the preset set at 4K from the top, the voltage strike will be Approx 3V, you can omit D2.

 

Have you considered using an LM3914 instead? It's designed for this sort of project.

 

It would be really easy to do this with a micro-controller. Simply parallel a voltage divider over the two terminals. The two resistors would have the same values, say 2 x 10k resistors. Then, plug the middle wire (now max 5v) of the divider directly into any analogue pin. Read the pin from the controller, then set an appropriate digital output pin to HIGH depending on the value. Ofcourse, you'd need a resistor wired in series with each led. Antony...

 

Have you considered using an LM3914 instead? It's designed for this sort of project.

I heared about that one. But will it work under 0 volt to 10 volt range properly?

 

It would be really easy to do this with a micro-controller. Simply parallel a voltage divider over the two terminals. The two resistors would have the same values, say 2 x 10k resistors. Then, plug the middle wire (now max 5v) of the divider directly into any analogue pin. Read the pin from the controller, then set an appropriate digital output pin to HIGH depending on the value. Ofcourse, you'd need a resistor wired in series with each led. Antony...

I know but this is costly and time consuming and require much effort.
And also I am a novice in electronics to implement microcontroller.

 

I know but this is costly and time consuming and require much effort.
And also I am a novice in electronics to implement microcontroller.

I disagree! I think it would cost around £3 and it would take me around 10 minutes to do! In my opinion, the way you're trying to do it now is more advanced!

 

But will it work under 0 volt to 10 volt range properly?

It needs a supply voltage in the range 3V to 25V but will happily measure input voltages in the 0V to 10V range, with suitable choice of 2 range-setting resistors. Here's a link to the datasheet.