Transistor LED Flasher
A simple LED flasher that uses only two transistors, one capacitor and one resistor. This basic oscillator can have other simple applications. (6/10/2006)
If you are familiar with LED flashers using transistor, you may know the basic one uses two transistor, one capacitor and three resistors. There is other kind of oscillator called "flip-flop". As I'm starting to develop some basic circuits, I need a simple LED flasher that can be used in many other applications.
After some hours thinking how to create a new simple LED flasher with the minimum components, I decided to use a simple RC. Here is the schematic of my two-transistor LED flasher:
The RC circuit is connected to the base of the NPN transistor (3904) and it gives the signal to the PNP transistor (3906) to turn on the LED. When the PNP transistor is ON, it discharges the capacitor and it turn off itself, so the cycle repeats again.
Also, if you want to drive crazy someone or yourself, you can use a speaker to simulate a water drop.
The resistor and the capacitor define the frequency. The circuit with the lightbulb may not work if the bulb works with 6 volts or its resistance is low.
12/26/2007 - Update:
While cleaning "the attic" a few weeks ago, I found this old project. This one uses the same circuit. It was made in 1996 or 1997. A 3 Volts lithium "coin" battery provides power up to 4 hours.
The idea of this one was to get a flashing light without bulky or heavy parts. Regardless there are some LED flashers on the market, A LED with integrated circuit inside the acrylic, the cost is higher than this circuit in some cases.
At least you can get an idea how to make a "coin-type" battery holder.
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