555 Timer problem

[electroniceddy]

Hi guys,

im in no way a pro, but a hobbyist, and i have been trying to create a 555 timer wihtout the use of a microchip (ie just with transistors) i have built the following circuit 4 times



and have added some stuff to the front in order to make an a-stable 555 timer, however on every occassion all im getting is a continuous output of on.. 4 different times, (first 2 on breadboard, the second two on circuit board)

is this actually a correct schematic for the 555 timer.?

im using

2n2222 Npn transistors
2n3904 Pnp transistors
and
1n4002 diodes

cheers

[virtualparticles]

OMG, this is very ambitious. Keep in mind that some of the transistors are used in strange ways because it is easier to fab a transistor than a resistor. If I were you, I would load this into LTSpice and analyze it there. The 3904 is one of the transistor choices and any old diode is fine. The 3904 might not have the needed properties for this though. You should be able to troubleshoot it that way.

[mikerj]

Trying to recreate an IC with discrete components using the original schematic is somewhere between difficult and impossible.  There is already a well proven discrete 555 design available as a kit and the datasheet pdf includes the schematic.

[Wimberleytech]

May be an issue with your flip flop.  Try changing the 5k connected to the diode, to 15k as shown in the schematic linked above by mikerj.

Also, put a resistor in series with the output LED.

[Achu]

I think you could build each sections like comparators, flip flop using transistors and connect them together at last.
This modular approach will have more chance of success I believe.




















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