This is a simple flashing led circuit with 2 leds and 2 NPN transistors. It illustrates the behavior of transistors and capacitors and if you use an oscilloscope it will be very easy to determine what ...

in figure 3 for a variable flash rate, replace the 220k pot with a 220k in series with a 22k resistor. And that is a simple 555 led flasher circuit.

In Figure 1, National Semiconductor's LM3710, a supervisory circuit, is configured to reduce the power consumption of a traditional LED indicator by 99%. When V IN is above 4.4 V, green LED1 ...

Today you can buy flashing LEDs; a simple two-lead component ... for all the world like any other LED, though embedded in the plastic dome is an integrated circuit to do all that flashing work.