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Op Amp LM358 LED flasher oscillator

  1. Sep 30, 2016 #1
    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
    Ti IC chip 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?
  2. jcsd
  3. Sep 30, 2016 #2


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    Here is my copy of your pic.
    So where's the fifth resistor and check the connections to the +ve input.

    I think omitting the non-inv input via R to +ve supply may be needed because not using split power and centre ground. If you omit it here, when op goes low the inv input can never get lower than non-inv.
  4. Sep 30, 2016 #3
    That is what I saw, missing resistor.
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