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LM3909 Simple Led Flasher

When we need to know where is the important thing in the emergency, some time we got any trouble, because we cannot to find that quickly. For example when we need a flash light at a dark night because the electric power is down, and many other cases. To overcome this problem, we can add an indicator that is contrast with the environment such as blinking light. Blinking light can be generated by using led sign flasher (as shown in figure). This main component (LM3909) can be used as oscillator (for another application) by changing the value of R and C (more detail information can be read at the data sheet).

Application is made simple by inclusion of internal timing resistors and an internal LED current limit resistor. As shown in the application circuits, the timing resistors supplied are optimized for nominal flashing rates and minimum power drain at 1,5V and 3V. Timing capacitors will generally be of the electrolytic type and a small 3V rated part will be suitable for any LED flasher using a supply up to 6V. However when picking flash rates, it should be remembered that some electrolytics have very broad capacitance tolerances for example -20% to + 100%.  

Figure 1. LM3909 led flasher.

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