Help required with 555 timer project

Discussion in 'The Projects Forum' started by Steve333, Aug 24, 2013.

  1. Steve333

    Thread Starter New Member

    Aug 24, 2013

    I'm new to electronics and am struggling to understand a circuit I've just made. I'm probably being really thick, so apologies if this seems really obvious or dumb.

    I've attached a circuit diagram of the 555 timer circuit, which I've assembled. It works as it should, however I don't understand which path the electrons are taking, as there seems to be so many possible different paths.

    My guess is that when I touch the fly leads together the electrons go across the fly leads, onto row H on the breadboard and then into the 'trigger' PIN on the 555 timer. They then come out of the output PIN on the 555 timer and onto the LED? But wouldn't that mean the LED would be the wrong way round? Or do they go through the LED, then onto the capacitor, and then once the fly leads are disconnected, then go back through the LED in the correct direction? If that's the case, however, wouldn't it mean the electrons would be going back to the 555 timer via the output pin? Would that be a problem?

    As I say, I've got it working and have fitted different value resistors and capacitors to change the timed interval, I just need help understanding the different routes the electrons take so I can visualise the current flow better. I'm particularly interested in the capacitors role, as I was under the impression current doesn't actually flow through it, as the electrons can't pass between the two plates.

    If anyone could give me any help it would be much appreciated.





  2. Wendy


    Mar 24, 2008
    The 555 Projects

    555 Monostable

    I am afraid you will have to learn how to read schematic if you want to trace the electrons flow. Protoboards are great, as you can see I use (and document them), but I would not even begin to try to really understand a schematic unless it is drawn out, it just makes things obvious.

    The 555 Monostable article that I wrote has a theory of operation, including electron flow.

    Do you think in conventional or standard electron flow? Standard convention says plus flows to negative, whereas the AAC book, where the article is located, uses standard convention (negative to positive). It is not too important, other than keeping track.
  3. wayneh


    Sep 9, 2010
    First, congratulations on getting it working nicely, and thanks for supplying pictures that detail what you're doing.

    The source of your confusion may lie in how you're asking the question. The main current flowing - that lights the LED - is NOT passing through the leads you touch. The current in the LED is under the control of an "active" component (as opposed to a passive component, such as a resistor or capacitor). That active component is inside the 555, and it determines the state of the trigger and then opens or closes the output in response. The main current only flows from the power supply to ground, through the LED and the "valve".

    The leads you touch are a different circuit, and a much, much smaller current flows in that loop. The smart, active components inside the 555 can watch that loop, though, and react accordingly.

    Many ICs have a similar property where a tiny current flow at the inputs is converted to a larger current flow at the outputs, using active components inside the IC to control power from the power supply.
  4. Bernard

    AAC Fanatic!

    Aug 7, 2008
    An easy ? way to visualise electron flow is to remember the old 6H6 theromeonic vacuum diode. A heater boils off electrons from the cathode, if a + voltage is placed on the anode [ plate] electrons are then attracted to the anode creating an electron flow. In an external ckt electrons flow from - to +, in a battery the flow is from + to _.