HEART FLASHER


This circuit is commonly called a RING-OF-THREE as it has three timing (or delay) sections to produce an oscillator.
It uses three transistors to alternately flash three sets of coloured LEDs and will operate from 3v to 9v. Two sets of LEDs are illuminated at any time and the third set is OFF.

 Principle of Operation
The circuit consists of three identical amplifier stages consisting of a transistor. Each stage is connected via a capacitor called an electrolytic. This is a capacitor with a high capacitance.
Connected to the electrolytic is a 10k resistor.
The reason why the circuit oscillates or "flashes" is due to a state called instability. The circuit is unstable.
It is very difficult to describe this circuit because it is UNSTABLE and there is no starting-point.
Let's start with the first transistor at the point where the circuit is first turned ON.
The circuit needs this turn-on pulse to start the "oscillation."
Suppose the first transistor is not turned ON. The second transistor will be turned ON via the 22u on its base being charged via the 560R and through the red LEDs. This will turn on the yellow LEDs and the third transistor will be turned OFF because the 22u on its base is uncharged.
 

The Circuit

The photo identifies all the components and how to fit them to the printed circuit board.
Use a constant-heat soldering iron (320 degrees C) and fine solder (0.8mm).
Fit one component and splay the legs slightly so it doesn't fall out of the holes. Turn the board over and hold the soldering iron on one side of the lead and the solder on the other side. The solder will melt and flow across to the iron. This will take less than one second.
Snip the leads close to the solder-joint. Solder one component at a time. Use the photo above to identify each component and how it is fitted to the board. All the components must be fitted around the correct way, and there is only one way to fit them. However the 4 resistors can be fitted around either way as they are classified as a "non-polar component."

The photo above shows all the components fitted to the board. You can see the flat on the side of the LED and the placement of the two electrolytics. The two 10k resistors are in the centre and the two 470 ohm resistors are at the edges of the board.
Connect a 3v to 9v supply to the 2-terminal connector with the positive on the left and the negative on the right. The circuit will not be damaged if the supply is reversed, but it will not work.
 

You can buy this kit for about $2.00 post-free

21-7-2013