Breadboard Astable Multivibrator

147

02:16:20

Help!!
I made this on breadboard but its not working.
I am using a battery for 9v input and BC547 transistors.
Please guide me.
Finally Got it. Its working perfectly. 

published 11 years ago

thebugger

11 years ago

Use a little more powerfull transistors like 2t6551 and smaller caps. You may need to recalculate your time constant. Increase the LED resistors to 300ohms and the base resistors to 20K-50k (depending on your time constant). Also remove the 100 ohm resistor in series with the power supply and you are good to go.

DJalaj

11 years ago

Ty for the help but i am still unclear about time constant. I know that t=log2rc but i dont know which values should be taken for this circuit

hurz

11 years ago

Checkout a little tutorial from @rbrtkurtz "Astable Multivibrator Comparison"

rbrtkurtz

11 years ago

Indeed. ;) Here's what I did. I threw out that 100R resistor. Then I swapped out the 150R current limiting resistors for the LEDs for some 330s. Plugged it in, and it worked. Oh, The transistors I used were 2N2222s, but just about any small signal transistor should work fine, I've used all sorts of them. So I guess my question is are you sure you wired it up properly? Try getting rid of that 100R, then increase the resistors for the LEDs so you don't pop them.

rbrtkurtz

11 years ago

Also, here are some other resistor/capacitor combinations to try that will blink at the same frequency. 4K7 & 470µF, 10K & 220µF, 22K & 100µF, 33K & 68µF, 47K & 47µF, 68K & 33µF, 100k & 22µF. Now, they don't really like being at either extreme (small caps and huge resistors, our huge resistors and small caps), so I suggest trying to find a middle ground. For this frequency (about .3Hz) I would go with like 47µF to 100µF caps, and the corresponding resistors. So maybe try using the 22K & 100µF combination.

alternativenergie

11 years ago

Thous 547 should be good for sustaining the LEDs but you must be careful at how you connect them in this circuit (base, emitter, collector ; see them at all datasheet.com) and you also should eliminate the 100 one resistor connected to the battery. Good luck!

DJalaj

11 years ago

Thanks @rbrtkurtz and @alternativenergie

Arjunc

11 years ago

Please use 470 ohm and 47 kilo ohm respectively.it will surely work

add comment in editor

EveryCircuit is an easy to use, highly interactive circuit simulator and schematic capture tool. Real-time circuit simulation, interactivity, and dynamic visualization make it a must have application for professionals and academia. EveryCircuit user community has collaboratively created the largest searchable library of circuit designs. EveryCircuit app runs online in popular browsers and on mobile phones and tablets, enabling you to capture design ideas and learn electronics on the go.