NPN Ring Oscillator

There is 4 destinctives to this circuit. 1. The time base is 5 seconds, this is 5 times slower than real time (1 second) 2. The RC time constant choice is set by the 20k resistor and the 100uf capacitor. 3. The circuit voltage is 5Vdc. 4. the max LED current set by the 100 Ohm resistor is approximately 28.3mA. Removing the diodes revealed that the 20k resistor was choking the base current to 203uA, this reduces the LED current to approximately 20mA, which is all well and good, but the transistor is being held down and is not free to oscillate. The is a few things that could be done to make the circuit more sensitive and more likely to oscillate, What ever you do, get rid of those diodes. Then either 1. Reduce the biasing resistors to15k, this will allow the biasing voltage/ current match the LED current limiting resistors, it will also change the selected RC time constant . Or alternatively 2. Increase the LED current limiting resistor to about 140 Ohms this will set the LED current to approximately 20 mA and leave the RC time constant alone. Here is the circuit laid out in the more conventional layout to aid in the analysis of what is happening. http://everycircuit.com/circuit/6658116113661952

Here is the circuit with the diodes removed and the LED current limiting resistors adjusted to140 Ohm. The start time could still be made shorter by playing with the resistors a bit more. I also prefer the 1second time base. http://everycircuit.com/circuit/5270037041774592

@BillyT : Thank you. I added the diodes because I have made a similar circuit and I used electrolytic capacitors. Your circuit is actually quite neat!

@mdchaara : the resistor values I used reflect the default transistor gain used by EC (100). If this was set to the actual gain of the transistors used, the resistor values used would probably line up without having to use the diodes. Note: the main difference between electrolytic capacitors and other capacitors is that electrolytics tend to leak, not only electricity but also electrolyte.

@BillyT Thanks for the update. I'll keep this one as it is, and I have created a new one, the "BillyT" edition :) link is below: http://everycircuit.com/circuit/5263803534278656

Original circuit without diodes, using transistors with a gain of 145. http://everycircuit.com/circuit/4974770220433408