stompbox reg supply plus batt indicator

[Paul Perry (Frostwave)]

An idea for a regulated stompbox supply - mentioned here before - is a 9v battery feeding a 5v regulator which then goes to a 7662 voltage doubler.
using a low dropout regulator like the LM2931 means your battery is good down to 6V.
It occured to me that putting a led & resistor across the regulator - from the input to the output - would give an light that varied in brightness accordign to the voltage drop across the reg, so it would be an indicator of battery strength.
But then I looked at an alternative.. if you had a voltage divider across the battery, say 5.1K from the battery +, then 9.1K to ground - you would get a voltage that decreases as the battery discharges, while the +5 stays constant.
Now if you run another led from the +5 regulator output to teh junction of the divider, you get the led coming on ONLY when the battery voltage has sunk past a certain point.

I suppose you could do it the other way around as well (double the battery voltage & use a 9v reg) which might be superior (I like the idea of the regulator being AFTER the doubler! because, it lowers the output impedance & removes any ripple) but, the +5 is what I had to hand.

[Sir H C]

Some LDOs have a low voltage flag that comes out.  That could give you a low voltage LED.

[Paul Perry (Frostwave)]

Some LDOs have a low voltage flag that comes out.  That could give you a low voltage LED.

Thanks, I didn't know that!
I do know it is getting progressively harder to find new regulators that are DIP..... people only want to build chips for cellphones & cameras..