A simple astable multivibrator, LED flasher

To test if transistored circuits with 2N3904 transistor can operate on 2.5V power supply I build a simple astable multivibrator. The components are of the shelf. I found some schematic. As on all my experiments, the value of condensators is readed from them, but value of resistors is measured.

I note some formulas describing the multivibrator.

The las thing I did is connecting som old analog meter to multivibrator and made some video of it.


//EDIT: 2008-10-12
On the schematic there are BC547, on the breadboard I hac 2N3904.
I havent time to buld an NAND gate, but what I did is chenge capacitors from 10µF to 5µF and build a second one multivibrator nexto to first. Its the same schematic, only capacitors have value 20µF.

2.5V Power Supply

Build a 2.5V power supply was the first step in experimenting. Because without a powers upply, no transistor will do anything useful.

As I remember, there has to be some LT317T chip somewhere in my boxes. I dig int them and found only one, but it's enough. Then I search the internet, just to find how it can be used. Some of the pages I found:

• LM317T Variable Voltage Regulator
• Using The LM317T To Regulate Voltage

I look for components I have and draw shematic. The value of resistor is measured, the values of condensator is read from them. The schema is on the right.

With schematic I began putting components on the breadboard.
The result is on the next picture. There is not much to see. Resistors are mounted vertically to save space and the 220µF condensator is so big. The LED diode is shining, because the power suply is under the power. The resistor on the host right part has no function. It's there only to allow me measure output voltage. The last picture shows the output voltage, It's 2.45V.