Simple LED Flasher Circuit for AC Power
The first circuit depicted in Figure 1 showcases an uncomplicated LED flasher designed for AC power operation, featuring six channels. In this configuration, all six LEDs flash independently and in a completely unsynchronized manner, resulting in a visually chaotic display. This setup represents an incredibly energy-efficient lamp bulb, consuming a mere 0.2 watts or thereabouts. To witness its functionality, refer to the brief video available online. This project incorporates my NPN multivibrator circuit, details of which are outlined elsewhere in this issue.
Each of the six NPN multivibrator circuits, connected here in series, draws an identical loading current. By adjusting the values of the electrolytic capacitors, you can modify both the flashing frequency and the brightness of the LEDs. If you desire a slower flashing rate, you can achieve this by selecting a charge resistor R1 with a value higher than 100 kΩ or by incorporating an additional resistor in the power feed.
Enhancing Safety with Low Voltage Operation
One significant drawback of the circuit lies in the potential risk of fatal electric shock, given its direct connection to the AC power line. Touching any component of the circuit while it is live poses an extreme danger. To mitigate this risk, it is absolutely essential to encase the project in a well-insulated, touch-proof plastic housing equipped with proper cable restraints. Figure 2 presents an alternative version of the circuit specifically designed for operation at low voltages ranging from 12 to 24 V. In this setup, the NPN multivibrators are powered in parallel, deviating from the series connection in the previous version. This alteration allows for the construction of longer flasher chains while significantly reducing the associated risks.
Understanding the Astable Multivibrator Principle
The fundamental principle underlying the Astable multivibrator involves a subtle variation in the electrical characteristics of the transistors. This variation causes one transistor to switch on faster than the other when power is initially applied, initiating oscillations. Astable Multivibrators serve various purposes, notably in delay and timing circuits, as well as in the transmission and reception of radio signals. In contrast, Monostable multivibrators are predominantly utilized in analog systems to regulate the frequency of the signal at the output.