The LED driver uses a CMOS 555 timer since it operated with low voltages and can work for about 190 hours when using a single NiMH battery cell rated at 2000 mAh. The 555 timer drives the transistor ...

Using a CMOS 555 timer and a single NPN transistor, you can drive as many as seven LEDs using a minimal amount of voltage and power from a single NiMH (nickel-metal-hydride) AA cell. The circuit works ...