I have tried many times testing some Op Amp LED flashing circuits on a breadboard from the internet. So far, none of them works. The photo above is one of my attempt using a LM358. I have double checked my wiring and swap the 100k with 10k and 56k resistors. what is the problem here? why it's so hard to get a led flasher working with an Op Amp? Also I notice some of the circuit diagrams in the internet don't have the left 100k resistor between v+ and non-inverting input. why is that?
The LM358 might swing its output to within 2V of the supply rail on a good day. That means on a 4V supply it might be able to muster 2V on the output. It barely reaches half Vcc in other words. Try lowering the 100 k resistor from the non-inverting input to ground to maybe 33k and see what happens. In effect you are lowering the target voltage which the capacitor has to charge up to to make it switch polarity on the output.
Wording above slightly changed due to an error pointed out by Michael Karcher.