Astable multivibrator

A couple of things... You've got the concept down. However, first of all, those current limiting resistors fir the LEDs are a little stout for 2V 20mA LEDs with a 5V supply voltage. I'll let you apply Ohm's Law to figure out what values would be best. R = V / I. Next, going with about 1/3 to 1/2 of the values you have set in the 47K resistors will forward-bias the transistors a little more, which will charge the caps quicker, and make the LEDs appear brighter. There's some exact science to it, and Wikipedia actually has a pretty good article on multivibrators, but the good thing about a sim is that you don't always have to do the math. You can fiddle around with values to see how components work together, and you can just fool around with then until it looks right. ;) Finally, some of your values are a little wonky. 22uF here, 21.9uF there, etc. It's not a huge deal, but it looks a little better when the values are nice, even, and standard. Also, the schematic could stand to have a few components moved around to clean up some lines and make things easy to follow. I'm just getting picky now though. :) Anyhow, it works, it does what it's supposed to do, there's just some minor issues. If you're interested in learning more, start with the Wikipedia article. http://en.m.wikipedia.org/wiki/Multivibrator

Thanks for the comments.Lowering the size of the resistors speeds up the charge and discharge rate of the capacitors and speeds up the flash rate.I suppose to get the rate back you could make the capacitors a little larger.

Very astute. Assuming that both sides are equal, the formula for determining frequency is a constant of .72 divided by RC. So 47000 ohms multiplied by .000022 farads equals 1.034. Divide that by our constant, and this thing should be flashing at .69Hz. So now we want to change our resistor values to bias the base of the transistors harder, but we want to keep the same frequency. Well our RC value was 1.034 for the frequency we want. We know that value, and we know we want 22K resistors. So we can do the division to see that we'll need 0.000047F (47µF) caps to keep the same frequency with our new 22K resistors. So go ahead, change the resistor values to 22K, and the caps to 47µF. Don't forget the current limiting resistors for the LEDs. They're 2V 20mA LEDs. You've got a 5V supply. So you'll want a voltage potential of 3V and a current of 20mA across the resistor. Using Ohm's Law, R = V / I, R = 3V / .02A, R = 150. It's all just a little, simple math. It gets trickier if you want to make the two sides different, but it's easy when both sides are the same.

Better yet, set one side with a 22K resistor and 47µF cap. Then set the other with a 47K resistor and 22uF cap. They'll be working at the same frequency, and you'll be able to see what's different about the two, in real time.

Cool