Site visitors are already familiar with the author under the nickname NEW PEW. These are the articles “Non-contact voltage indicator” and “How to make an infrared proximity sensor.”
In this article, he will introduce us to another of his work. The peculiarity of this circuit is that no IC (integrated circuit) is used for variable switching on of LEDs.
How this circuit works will be described in the last step.
Tools and materials: -2 LEDs; -2 transistors BC547; -470 Ohm resistors – 2 pcs; -2 10 kOhm resistors; -2 100 uF capacitors; -Soldering accessories; -Third hand;
-Nippers;
-Battery 9V; -Battery terminals;
Step one: resistors
First we need 470 ohm resistors. Bend one leg of both resistors 90 degrees. Then solder the bent legs together.
No matter how the resistor is placed, it works the same in both directions.
Next we need 2 resistor 10 kOhm. Cut off a piece of leg on one side of both resistors. Then solder the resistors to the resistors from the previous step (see photo).
These resistors do not need to be 10K ohms. Anything between 10K and 50K can be used. The resistor value will affect the switching speed between LEDs.
Step two: transistors
Now let's move on to transistors. First we work with the first transistor.
Bend the collector and emitter leads of the BC547 90 degrees. Solder the collector to the 470 ohm resistor and the base to the 10k resistor.
The last image is the pinout of the BC547 transistor.
Now the second transistor .
Bend the collector and emitter leads of the BC547 90 degrees. Solder the collector to the 470 ohm resistor and the base to the 10 k ohm resistor.
Step three: LEDs
Bend the legs of the LEDs so that they are at a 90 degree angle to the LED and to each other. Solder the anode (+) of the first LED to the emitter of the first transistor. Solder the anode of the second LED to the emitter of the second transistor.
Connect the cathodes (-) of both LEDs together and solder them.
Step Four: Capacitors
For this project, 100 uF capacitors are used. Any value between 10 μF and 100 μF can be used.
These capacitors have polarity.
Install the first capacitor, the “+” leg between transistor 1 and the 470 ohm resistor. Install the second leg of the capacitor “-” between “transistor 2 and the 10 kOhm resistor.
Install the second capacitor leg” + “between the” transistor 2 and the 470 Ohm resistor. Place the second leg of the capacitor “-” between transistor 1 and 10 kOhm resistor.
Step five: power supply
The master uses a 9V battery as a power source. The plus of the battery connects between the pairs of resistors, the minus connects between the LEDs.
Everything is ready.
Now how it all works.
The base of both transistors is connected to + via a resistor. Either of the two transistors is activated first (this is because neither transistor is similar to the other and is triggered simultaneously). Suppose transistor 1 turns on first. When the transistor turns on, the collector pin is grounded and the LED lights up. Also, the capacitor begins to charge through the ground, provided by the 1st transistor and a 10kΩ resistor connected to the base of the 2nd transistor. The 1st capacitor is charged and no current flows to the base of the 2nd transistor. At some point, the 1st capacitor will be charged. And when this happens, current no longer flows through it, but begins to flow to the base of the 2nd transistor. The 2nd transistor is activated and the second LED lights up. At the same time, the second capacitor starts charging, and the first transistor closes. And so on until the battery runs out.
You can watch the assembly and operation of the device in the video below.
