From the MAKE Flickr photo pool
Flickr member Kc7fys built this fine little voltage meter to indicate battery level using a bi-color LED and an LM358 op-amp chip –
I could measure the resistance values and just use regular resistors to make it smaller. It tells me when my radio power supply (battery pack) is 12V or above, 11-12V, or below 11V with three colors in the LED.
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