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.
  • #71
What does the writing on the 555 chip actually say? Could you read it please?
 
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  • #72
One last silly question: Is that electrolytic cap connected with (-) lead to ground?
 
  • #73
Still no dice guys...light stays on, and the timer is actually STILL getting hot. Could it simply be the breadboard? If so, I might make an attempt at soldering the circuit together instead.

Just reading back through the posts, I saw this one (above).
If you can get away from the breadboard approach, it would be good. You don't need printed circuit boards. I find breadboards generate more problems than anything else, usually because of poor connections.
This is a simple and extremely reliable ciircuit and it shouldn't be causing so much grief.

You turn the chip so its legs are facing upwards. (this construction method is called "dead bug construction" for this reason).
Any legs that are to be grounded are bent downwards and soldered to the PC board. Also any capacitors etc that need to be grounded are soldered in.
Power leads etc are attached to tag strips and not directly to the IC. (I use header pins cut to shape as tag strips).
This way, you can lay out a circuit as it is in a diagram and quickly see if something is wrong. It is very safe and the IC is in no danger of being pulled apart. And you can easily change a component value if you want to.


What does the writing on the 555 chip actually say? Could you read it please?

.
 
  • #74
vk6kro said:
What does the writing on the 555 chip actually say? Could you read it please?

LM393? :smile:
 
  • #75
LM393...Where did you get that?
 
  • #76
It's a joke. The 393 is also a common 8-pin PDIP part.
 
  • #77
What does the writing on the 555 chip actually say? Could you read it please?

http://www.radioshack.com/product/index.jsp?productId=2062596

Would you guys consider Radio Shack to be a distributor of quality merchandise of this sort?

One last silly question: Is that electrolytic cap connected with (-) lead to ground?

Yes.

This is a simple and extremely reliable circuit and it shouldn't be causing so much grief.

:cry:

At this point, all I there really is to blame is the breadboard, I completely agree.

During the past 3 or 4 days I have been posting here, has anyone been able to replicate my exact circuit?
 
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  • #78
Twinfun2:

I repeat: measure the resistance between all of the nodes in the circuit, with the 555 installed, but without power. There are only a handful of nodes, so this should only take a few minutes. With this information, we can hopefully positively identify your problem as a bad breadboard.

- Warren
 
  • #79
I found a very old 555CN chip and made up your circuit.
AND I got the same result as you did, but without any heating. The LED was on all the time. I checked with an oscilloscope and there was no other oscillation going on.

It will not oscillate with a 100 K resistor unless the supply is less than 4.5 volts.

To oscillate at 6 volts the 100 K resistor has to be about 10 K but no more.

So, you might like to try that. Use just 3 alkaline AA cells to get 4.5 volts or get a 10 K resistor.

A data sheet I found gives 100 K as the upper limit on this resistor.

I'm sure I have used 555s that were a lot less fussy than this one. Guess it depends on the maker. Mine was obviously ***P quality.

If the Radio Shack is convenient, you could try one of these:
http://www.radioshack.com/product/index.jsp?productId=2062595
It is the CMOS version of the 555 and should let you use any resistor you like.

I was also going to suggest you pick up a cheap digital multimeter, but not from there. Overpriced and poor features.
This is the sort of meter I was thinking of:
http://www.altronics.com.au/index.asp?area=item&id=Q1053A
that is about US$7.50

but Australia is a long way from Philadelphia.
 
  • #80
There's really nothing wrong with his meter. Nothing you're going to do at the board level is going to require more than 1% precision, so just a couple of significant figures is plenty. You can easily read a few sig figs off an analog meter. The only advantage of digital meters is that you can read them a little more quickly. They may appear to have greater precision, but their least significant figures are mostly noise anyway.

- Warren
 
  • #81
The non zero voltage readings in the following chart should have all been 5 volts. Because of the low resistance of the analog meter, much lower readings were obtained.
This was the test where the chip was removed from the socket.
1: 0v
2: 2v
3: 0v
4: 5v
5: 0v
6: 2v
7: 4.5v
8: 5v
 
  • #82
vk6kro:

The readings that were obtained have nothing to do with his meter.

The voltages on pins 2 and 6, etc. should not be 5V, and it's ridiculous of you to assert that they should have been. C1 had not been properly discharged, so it had some residual voltage on it -- nothing is driving that node.

There's nothing wrong with an analog meter -- certainly, nothing that's going to make his small 555 circuit fail to work. You're leading him down a frankly idiotic path.

I am a little concerned, though, about the voltages on pins 4 and 8 (RESET and VCC) being 5V, rather than 6V. If you're using 4 AA batteries and the voltage is sagging all the way down to 5V, you must be pulling a lot of current through them... what's the voltage of the battery pack when it's not connected to the circuit? What's the voltage when it is connected to the circuit? Are they substantially different?

- Warren
 
  • #83
The readings were taken under power from 4 AA rechargeable cells.
This means that the capacitor was fully charged and that the voltage should have been about 4.8 volts (4 times 1.2 is 4.8 volts).

So, since there was no current flowing in the resistor chain (after a 1 second charging time), the supply voltage should have been across the capacitor.
So there should have been 5 volts there.

The only thing wrong with his analog meter is that it is a low impedance device trying to measure high impedances. Better digital meters have a 10 Megohm resistance even on the low voltage ranges, but even cheap ones have 1 megohm input resistance. The error in this case was up to 60%, quite enough to lead him to the wrong conclusions.

I actually prefer an analog meter, but I wouldn't use one in this case.
 
  • #84
chroot said:
... what's the voltage of the battery pack when it's not connected to the circuit? What's the voltage when it is connected to the circuit? Are they substantially different?

Good idea to check these. Either the analog meter is somewhat off, or the unloaded battery voltages are that low, or the batteries are being drained when connected and that is pulling their voltage down.

I'll just add, try measuring the connected-battery-voltage both with and without the chip in the circuit. EDIT: but don't leave the chip in AND battery connected very long, due to the overheating chip issue.
 
  • #85
vk6kro said:
So there should have been 5 volts there.

Well, I looked through the analog meter's manual, and am very surprised to see that its input resistance, when set to the 25V scale, is only 20kohm. As you said, that's definitely low enough to cause problems here. Please accept my apologies -- I just never expected any meter to be that poor.

It does achieve 2Mohm resistance, but only on the 1000V scale...

- Warren
 
  • #86
~10-20k is a typical low-scale input impedance for basic analog meters--even the venerated Simpson 260 only had a 20k input-Z. Better ones incorporate a FET to raise the effective impedance to the low tens of MOhms.
 
  • #87
Yeah, I made the (apparently really bad) assumption that all modern meters use the same kind of sensing circuitry (FET input stage, for example), and that the only difference is the display... and I was wrong!

- Warren
 
  • #88
chroot said:
Twinfun2:

I repeat: measure the resistance between all of the nodes in the circuit, with the 555 installed, but without power. There are only a handful of nodes, so this should only take a few minutes. With this information, we can hopefully positively identify your problem as a bad breadboard.

- Warren

Roger, I will do this when I get the chance, but I am away from home again (Been a busy few weeks).

Sorry for such a late update.
 
  • #89
chroot said:
Well, I looked through the analog meter's manual, and am very surprised to see that its input resistance, when set to the 25V scale, is only 20kohm.

Wow.

Weird, I looked through the manual and could not find that info. Are you looking at something other than:
http://rsk.imageg.net/graphics/uc/rsk/Support/ProductManuals/2200223_PM_EN.pdf
?
 
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  • #90
Very last page, bottom of right column: "Specifications."

- Warren
 
  • #91
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?)
 
  • #92
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
 
  • #93
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.
 
  • #94
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.
 
  • #95
Does it heat up if you only connect + and ground?
 
  • #96
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.
 
  • #97
ShadowPho1 said:
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.
 
  • #98
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.
 
  • #99
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?
 
  • #100
Here we are at 100 posts for the NE555. That's over 12 posts per pin on an 8-pin DIP. Wow.
 
  • #101
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.
 
  • #102
Twinfun2 said:
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)
 
  • #103
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.
 
  • #104
vk6kro said:
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! :wink:
 
  • #105
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.
 

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