LED Flasher

LED Flasher:  Schematic, Simulation and Layout

This project focuses on simulating a low-voltage digital replacement for the classic LM3909 LED flasher circuit. The original LM3909 was a widely used IC designed for low-power flashing applications, such as LED indicators and emergency lights. However, since the LM3909 is obsolete, this project seeks to replicate its functionality using modern low-voltage, low-power Schmitt trigger devices.

By utilizing Schmitt triggers, the circuit can achieve similar timing and stability characteristics as the LM3909 while maintaining low power consumption. The design ensures efficient operation at low voltages, making it suitable for battery-powered applications. Additionally, using digital logic instead of analog components allows for greater flexibility in modifying the circuit parameters, such as flash rate and duty cycle.

One of the challenges solved is to find the correct model.  The model used was done in 2018 by a moderator on the TI Forum in a response to a request by a user for this model.  This model works far better than the official TI PSPICE  model that is just plain faulty.

This project is ideal for hobbyists, students, and engineers looking to recreate the LM3909 circuit using modern digital components. The simulation will help verify the circuit’s behavior before building a physical prototype. Any insights gained from troubleshooting the SIM error will also benefit future projects involving circuit simulation in EasyEDA.

If you have encountered similar issues or have alternative solutions, please share your thoughts to improve the simulation experience.

Circuit options

The circuit is designed for two options, a 1.5 V cell or a 3.7 V LiPo cell.

The component values shown is for the 1.5 V cell.  On an Alcaline battery the circuit should work for 4 years.

The SIM can be used to find the best component values for the LiPo battery.  When using the LiPo battery the discharge protection circuit saves the battery so that it can be successfully recharged.

Any comments appreciated.

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