Why is my 555 Timer not blinking?

In summary: Okay, I was assuming Vo=Vs when the output is high -- that has been my (limited) experience. I was unaware that this is not necessarily the case for all 555 timer variants.
  • #106
Probably, R... Shack have a bad batch and they are selling them to you already bad. There was nothing wrong with your circuit.

Could you get a couple from somewhere else or (better option) get the CMOS ones? They cost the same at Radio Shack and you can have resistors up to megohms in resistance.

With CMOS ones, you can have a simpler circuit. You leave pin 7 unconnected and take a resistor to pins 6 and 2 from the output pin, pin 3. Gives a 1:1 square wave so that is fine for a flashing LED.

Maybe get a 10uF tantalum capacitor. Electrolytics can be a bit leaky when used as timer components.
 
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  • #107
Well, most semiconductor companies keep their product output at a failure rate of less than 10 parts per million, so it would be literally incredible for an entire batch of parts from Radio Shack to be bad.

I strongly suspect something is just wrong with the breadboard, and the nets need to be ohmed out (tested for continuity) and the currents through the important pins need to be measured. With that info, we could positively identify the problem as a bad breadboard.

- Warren
 
  • #108
I would have to agree about the reliability of semiconductors. I have never proven a new IC to be faulty although I did get some diodes that were marked the wrong way around.

However, chips that get hot when the power supply alone is connected are faulty. Do you buy more chips from the same place just to prove the point?

We have already suggested wiring up the circuit with soldered joints and not using the breadboard. That is what I would do and I'm sure it would be working in 10 minutes.
 

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