I found a circuit online that creates a strobe effect between two LED's. I have redrawn the circuit diagram to simplify the layout, as below:
I have built this circuit on a breadboard and it works as expected. The issue I have is the implementation of the LEDs.
My two lights have two internal LED's (white and yellow) each with a shared negative/ground (i.e. 3 wires per light). I plan to run this strobe circuit through the one of the LED's (white) from each light; however, the current set-up works with a shared positive for the LED's and not a shared negative. As such, if I were to wire my lights into this circuit, I wouldn't be able to run the second LED (yellow) as the circuit would effectively 'short' across the negative poles.

Is there a way to reconfigure the above circuit such that the LED's have a shared negative connection rather than the shared positive as above?
The only possible option I could come up with was effectively swapping all the components around; however, this put the LED's on the emitter side of the transistors which increased the current flow through them and effectively eliminates the strobe effect. This can probably be rectified by changing the combination of capacitors and resistors, or possibly by switching to PNP transistors, but I'd prefer to avoid buying more components if possible.

Thanks for the assistance.

 

You would only have to purchase PNP transistors, all the components remain the same. Just remember to polarize your electrolytic caps correctly.

 

The easiest way would be to flip the circuit and use PNP transistors.

The circuit you have is a classic astable multivibrator circuit, normally draw as follows (captured from Wikipedia).



In your case, R1 and R2 are replaced with LEDs.

 

In your case, R1 and R2 are replaced with LEDs.

Would it be more accurate to say “place an LED in series with R1 and R2.”?

 

Is there a way to reconfigure the above circuit such that the LED's have a shared negative connection rather than the shared positive as above?

 

Thanks WBahn. That makes sense. I'll read up a little more on the astable multivibrator circuits and make sure I understand how they work.
Another quick question: If I wanted to adjust the tempo of the oscillations would I be able to incorporate a variable resistor into the circuit?

 

Would it be more accurate to say “place an LED in series with R1 and R2.”?

I would tend to think so, but I certainly see this circuit all the time with an LED simply replacing R1 and R4 (my mistake in saying R2). I have never actually played with this circuit, but it seems like R2 and R3 need to be chosen so as to place the transistors into saturation, so that would argue against adjusting their values so that the transistors limit the current. My gut feel is that the circuits that omit the limiting resistors are having much more LED current than they realize. Also, the forward drop of the LED is going to change the timing equations quite a bit.

Personally, I would probably just add the LEDs across the collector-emitter terminals of the transistors, but that would prevent the collector voltages from rising to Vcc when the transistor is off. This is going to completely change the equations that govern the frequency, but that might not be a bad thing -- it might even result in somewhat better power supply rejection.