I am working with a LM555CN and I am trying to have it run in astable mode and make a LED blink. In essence I am trying to follow along with this video.

Now, there is a part in the chip instructions where it tells you how to set it up in order to have it run with a 50% duty cycle.

enter image description here

Here is the part where I am not understanding correctly and I would like someone to explain this to me.

enter image description here

The way I read this (which is wrong apparently) is that these 2 resistors are connected in series (effectively creating a voltage divider, right? Not right?) where the end of the second resistor goes to pin 7 and the half-way point goes to pin 6 (and 2).

In the image attached below, the bottom pair is how I implemented it. The top pair is how it's implemented in the video.

I perceive my implementation as what I see in the schematic, yet it does not work as expected. The LED does not blink and stays on (or it blinks very fast, not sure).

If I make the connections as shown in the video (top pair), it works as expected.

This is where I cannot really wrap my head around how things work with the way they are connected in the video.

The way I see it, the resistors are connected in series again, but this time the half-way point feeds to pin 7 and the end of the 2nd resistor feeds to pin 6, which is not what I see in the schematic.

enter image description here

  • 2
    \$\begingroup\$ The groups of 6 holes are connected together horizontally as you are looking at them, so in the lower photo pins 6 and 7 are connected together and the resistor is shorted out. \$\endgroup\$
    – Finbarr
    Mar 15, 2021 at 20:31
  • \$\begingroup\$ @Finbarr hm, so after the 1st resistor, the current completely bypasses the 2nd resistor (and pin 7) since it can pass through the red wire jumper? \$\endgroup\$ Mar 15, 2021 at 20:36
  • \$\begingroup\$ It bypasses the resistor because its ends are connected together. \$\endgroup\$
    – Finbarr
    Mar 15, 2021 at 20:38
  • \$\begingroup\$ Oh! I think I get it. So, it's like I have created something like this? \$\endgroup\$ Mar 15, 2021 at 20:44
  • \$\begingroup\$ @Finbarr Feel free to write an answer if you want the points. I now understand my error, thanks \$\endgroup\$ Mar 15, 2021 at 20:56


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