Can anyone suggest or point me in the right direction for a low-battery indicator circuit for use with guitar and stomp boxes? (9v pref.) Somehting like a warning LED coming on when the battery falls below a certain voltage, or even better, making an existing indicator LED in the circuit start to flash on/off - that would be great!
"The best way to do it...is to do it." - Amelia Ehrhard
Here's what I do, not as quick as gaving a circuit built into each box, but quicker than opening it up to test the battery directly.
I check my batteries with a a bit of a cheat, which is a probe comprising a stereo jack plug with two wires to just the ground and ring connections. These wires then go to a multimeter to read voltage.
It works because when in normal use, these two connections are shorted by plugging in a normal mono jack, which is how power is connected by joining the internal battery negative to ground. When the probe is inserted instead, it reads the battery voltage, via the devices circuitry. This ressults in the reading being a bit low, by maybe 1/2 volt, but I check it with a fresh battery, and afterwards I can quickly see whether it has decayed.
The other thing I find with my stomp boxes is that the normal indicator LEDS start to fade away visibly before the sound is affected too much.