Why is my 555 Timer not blinking?

[Redbelly98]

Looked there, and saw:

Ranges...Resistance: 2k, 20k, 2M (Center Scale 20 ohm)

Sensitivity...DC Voltage: 20,000 Ohm/Volt​

Don't see anything else that relates to meter impedance. But I also admit I don't understand the remarks "Center Scale 20 ohm", or what the Sensitivity spec means. Do one of those somehow indicate 20k impedance on the 25V scale?

(Unless you're saying that the list of ranges for resistance measurement relate to meter impedance somehow?)

 

[chroot]

Yeah, it's pretty confusing, and I'm not sure I understand it. The highest possible resistance is 2M, though, and that clearly must be in the largest scale, 1000V. The smaller scales must have lower resistances, so... it can't be any more than 20k on whatever scale he's using.

- Warren

 

[Redbelly98]

Hmmm, I thought those numbers (2k, 20k, 2M) were just the max scale readings for doing resistance measurements. Not convinced they have anything to do with meter impedance.

 

[negitron]

Multiply the sensitivity in Ohms/volt by the full scale value of the range in question to get the impedance for that range in Ohms. For example: if the meter has a 1-volt range, the impedance will be 20 k; for a 5-volt range, the impedance will be 100 k.

 

[ShadowPho1]

Does it heat up if you only connect + and ground?

 

[vk6kro]

You can calculate the resistance of the meter if you assume the readings are accurate and the capacitor is not faulty.
It comes out as 73.529 K
So, 73.529 / (73.529 + 110 ) times 5 volts = 2 volts.

Given that this meter is 20000 ohms per volt and it was probably on the 5 volt scale, it should have had a resistance of 100 K as Negitron pointed out.
This may mean that the capacitor is leaky or that the meter is inaccurate enough to give this discrepancy.

Twinfun: have a look back about a page to item 79 in this thread.

 

[Twinfun2]

Does it heat up if you only connect + and ground?

That question was asked way back in the thread. Yes it does.

I most likely will wind up skipping 555 timer chip, because this is causing me way too much grief. I'm trying to learn about basic electronics for all main pieces of hardware before I start learning how to use my Picaxe starter kit (just to be safe), which really won't require a 555 timer any time soon. Is there any other IC's that would come in handy that do things that the Picaxe can't already do?

Again, thanks for all the help.

P.S. I'll still try and get those extra ratings when I get back home.

 

[negitron]

The thing is--and I do understand this has been a source of frustration for you--there's something fundamentally wrong here. This is not a difficult circuit and troubleshooting should not be this complicated. I'm not intending to pick on you here nor make fun of you (lord knows I've had my hsare of head-pounding frustration only to realize the solution was blindingly obvious) but until you can get this really basic circuit working, you probably don't want to get too far into anything more complex. Perhaps you should take a step back, however, and put this on the back burner for a day or two and then tackle it again with a fresh head. You can do this! Just take your time.

 

[vk6kro]

If the chips get hot with just the supply voltage on them, then the chips are probably faulty. You can't fix faulty chips.

Good news about the Picaxe kit. Amazing chips and a great programming language. Which one did you get?

 

[Bob S]

Here we are at 100 posts for the NE555. That's over 12 posts per pin on an 8-pin DIP. Wow.

 

[vk6kro]

That's right. There is a lot of interest in these chips.
Look at the views on the main page too. Currently 1061 views.
We covered some good fault-finding techniques, so hopefully it was educational, at least.

 

[ShadowPho1]

That question was asked way back in the thread. Yes it does.

Then something is horribly wrong with the chip, power supply or the breadboard. :)
Do you have a different 555 chip you can use?
How far do you live from Chicago? (I can test one and send you one if needed lol)

 

[vk6kro]

Driving to philly, I'll be back in 2 hours perhaps. (post #32 in this thread)

Guess this means Philadelphia. About 666 miles from Chicago.

It would be good if you could get the breadboard sent to you so you could tell us all what the problem was.

 

[Twinfun2]

If the chips get hot with just the supply voltage on them, then the chips are probably faulty. You can't fix faulty chips.

Good news about the Picaxe kit. Amazing chips and a great programming language. Which one did you get?

28X1

Ok, well as it seems by you guys that this thread is of high concern, I guess I'll keep on trying.

What I think I did was when I plugged in my new 555 timer into the approved circuit a few posts back, I had the same problem, in which I am sure has burned my new 555 timer. I am here left with 3 burned 555 timers. What I am thinking of doing now is trying to build a monostable circuit instead of an astable circuit; the monostable circuit I tried worked fine in driving a PnP Transistor to make a police siren. I will have to go to Radio Shack to get another timer, or maybe even try to turn in the 555 timer I just burned, saying that it came defective.

I'll try my best to get this to work!

 

[Redbelly98]

Since you have had a working monostable circuit, it sounds like a good idea to go back and build it again. After you get it working, I'll suggest:

Put your LED+resistor on the output of the monostable circuit, and make sure that works.

See if the LED monostable circuit works with just 3V Vs. If not, try 4.5V. Using a lower Vs will at least not heat things up as much, and might save on frying more chips in the future.

Then, leaving the chip in place, change the monostable circuit into the astable one.

Also, you might try buying 2 or 3 555's, instead of just 1. Don't know how much they cost or what your budget is like, so that's really up to you.

 

[vk6kro]

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.

 

[chroot]

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

 

[vk6kro]

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.