Police Lights

Change capacitors to 10micro F from 100 and change simulation speed to 1s/s

Go to 1uF for even faster flash, change your 1kOhms to 450Ohms too, better power response with the LED

The 1K resistors are about right for 2V 20mA LEDs at 20V. They can handle more, but you usually want to shoot for the typical ratings, rather than max ratings. As for the blinking, set simulation speed to 1s/s. The 100 microfarad (uF) caps will have that thing blinking pretty slow. I'd say anything from 1uF to 10uF is what you usually see in an astable multivibrator LED blinker. Using caps below .47uF will begin making the blinking too fast to see with the naked eye, and anything above about 47uF starts to become painfully slow. Those ranges aren't set in stone anywhere, I just use them as a general rule-of-thumb. For a police light effect, try the 10uFs, and go from there. The smaller the cap, the faster it flashes. Also, 20V is kind of a lot to drive just two LEDs. Something between 9V and 3V is more common. Of course, if you use less voltage, you'll want smaller resistances at those 1Ks.

Why doesn't your vibrator work? Did you try changing the batteries?

Thanks everyone (apart from the perv.) It's working nicely now!

Oh my sweet maple donuts! Why?! Everybody attempts this circuit, but NOBODY gets it right. Where is everyone getting the idea for all these cooky component values? Cracker Jack box? Seriously- who told this kid to use 400milliOhm resistors? That's... that's just silly. @fawlty- even on one of the harshest spikes this is producing, your LEDs still won't draw even 1mA! We're looking for 20mA- Ohm's Law my friend, put it to use! That little theorem is ever present and unfailingly in effect and when things seem too complicated or just aren't working out right, a little math will reveal the answer! 47 or even 100uF caps won't necessarily be too slow- correctly balance the rest of the circuit and you can easily achieve optimal frequencies. Play with the math, experiment and you'll get it. Here a hint: components were given the common values we see for a REASON- try using normal everyday values and things might start working in your favor! Oh and, I've had my share of some cruisers' flashing lights at my six so I can

...safely say they don't use ultra violet. Ok- thank you and good night...

*snaps fingers* guuuuuuurl you just got told !

lol those things weren't there the first time I looked at this. 400 milliohm lol. 47 or 51 ohm will be about right, using common components. You really need to research how astable multivibrators work. There's more to it, but basically, the caps are going to set the overall frequency, and the resistors at the bases of the transistors will control the amount of time the current is at peak. With big resistors (like 100K), you'll have a sharp spike. With small resistors (like 10k), you'll have more of a square wave, which will keep the LED at peak current longer. As a rule of thumb, I start at 47. 47K ohms for the resistors, and 47uF for the caps. If I want a higher frequency, I use smaller caps. If I want the LEDs at peak for less time, I use bigger resistors. And vice versa. There's more to it than that, and your input voltage will change things, too. But that's a basic way to look at it.

Also, I have some 435nm blue LEDs, I don't think he's into UV yet. ;)

Yep... a vibrator in hardcore policeman style !!! So we have a hot product here horny leds ladies stays in mile long queue to get one and blinks those nasty ..... ehem! ok my advice is throw away caps those are boring and static and we want dynamic like dynamic are our wrecks in garages with oversized engines and rear wheel drive so we make our wreck perform slide-dance on some shop parking like some prima ballerina on wheels. Throw trannies they're old grandpaa's. Longer on market than tubes were. Chose bioorganic neural bounded third level cauterization performed smokable radio-banana active chemo-skin ......and we shall have.....peace SIC!

Hey! Give me a break. I know nothing about electronics... it's trial and error. I'm trying to learn. Got to start somewhere!

Ok... thanks for the helpful comments. I adjusted the circuit as suggested :-)

it is uzualy

Nultivibrator