Pin 4 should be connected to the positive rail, not to ground. The way it is now keeps it in reset forever.
The timing capacitor is in backwards. The stripe should go to ground.
With the thing wired like it is, the red LED should be lit all the time. If it isn't, then either the LED is in backwards, it's bad, or the 555 is bad.
The LED current limiting resistors are too small if you're using a 9V supply. They should be:
Vcc - Vled R = ------------ Iled
Where R is the resistance in ohms, Vcc is the supply voltage in volts Vled is the LED forward voltage drop in volts Iled is the LED current in amperes.
Assuming about a 1.2V drop across the LEDs and a 9V supply, those
through the LED's so, if you're using 20mA LEDs, you may have burned one (or both, maybe) of them out. Test them by connecting them (one at a time) in series with a 1000 ohm ohm resistor and connecting that circuit across a 9V battery, like this: (view in Courier)
+---[+BATTERY-]---+ | | | | +--[1kR]--[LED>]--+
Make sure that you don't connect the circuit backwards, since if you do you could pop the LED.
Astable oscillators require Pins 4 and 8 to be high I don't see that in what you've built - looks like four is tied to ground.
Leds won't withstand much reverse voltage so you may have killed it
There's only a few schematics on that page - Which one? "simple 555 testing-circuit of Fig. 5?"
If it isn't working you didn't build it correctly or have a defective part(s)
When in doubt go back to the schematic and take your meter and measure each pin on the IC itself and see if you get what you expect to find (EG 4-high, 8 high, 1,zero, 5=2/3 the supply voltage, 2,6,7 rising when power is applied, then going lower and repeating, 3 toggling.
That proves out your circuit for correctness and the breadboard connections
Understand the theory of operation for the 555 and the astable oscillator and then check to see if it is doing what you expect - don't assume it is connected because it looks connected - measure with a multimeter
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I connected pin 4 to the positive rail, I dont know how I missed that.
Alright, I was under the impression that the stripe should connect to positive. What happens when you connect capacitors in backwards? From my experiments they appear to work the same. But I must be wrong again.
I'm pretty sure I've toasted all of my 555s, because with these modifications still no LEDs go on or off.
Finally, I've tested various resistance for my LEDs, and 100 is my favorite. I like my LEDs nice and bright :)
I'm going to yet again buy more 555 chips today and see if this thing works.
Assuming you have a breadboard, just wire pin 1 to ground, pin 8 to your +V supply, and then connect pins 2 and 6 together. This will give you an inverter, so when pins 2 and 6 are connected to ground, the pin 3 will be "high", ie about the same voltage as your +V supply. Connect pins 2 and 6 to the +V supply, and pin 3 will go "low", ie at 0 volts, or very close to it.
If that works, it's a strong indication that the 555 is still good. (I pretty much never have worried about pin 4, I've never had a problem with it just being unconnected, on the other hand if it gets grounded the 555 is in effect disabled.
Once you get used to the breadboard, little tricks will help.
I can never remember which lead is the anode on LEDs, so if I was wiring it so the 555 going low turns it on, I'd connect the resistor to the +V supply, the other lead to the LED, and then ground the other lead of the LED. One way, it will light, the other way it won't. Once that's figured out, then just lift the ground lead and connect it to the output of the 555.
A combination of simplifying and understanding helps to figure out what's gone wrong. Making sure the LED is wired right without the 555 is simplifying. So is that trick about using it as an inverter. You can even do things like put in a much smaller value capacitor (to avoid the issue of getting the polarity right on the electrolytic), so the 555 will be oscillating at an audio rate, and run the output of the 555 into an audio amplifier to see if there is a tone.
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Unless they\'re polarized electrolytic capacitors, nothing.
Otherwise, connecting them backwards will cause the oxide layer
separating the plates to dissolve into the electrolyte, shorting the
plates
I tried this out and neither of the LEDs goes on. All I can say with certainty is that whenever pin 1 is connected to ground, and pin 8 is connect to +, no LED will ever light up. Ever. This has been true for every single 555 I've used, and I've gone through 5 of them.
Assuming generously that 1 in every 1000 555 chips is defective, the odds of all 5 of my chips being defective are 1 in
1,000,000,000,000,000, and I refuse to accept myself as being that unlucky.
I have no idea what is going on here. My LEDs work, the capacitor works, and I try the simplest f***ing thing and it doesn't work.
Set it aside for at least a day and a night - "sleep on it", so to speak, and do something completely different for awhile, like go to a show or a game, or even just a Nature walk in the park - Then go back to it the next day, and double-check all of your connections again, and write down what each connection goes to.
In other words, take a decent break from the thing - it's hard to check your own work right on the spot, but if you give it a while, and forget about it as much as you can, you'll see it in a fresh perspective.
There is a picture of the components and wiring for a 555 that blinks one LED from a 9 volt battery here. It's about 2/3 down the page. The picture shows the top of the 555 with the pins pointing down. Note there is a little nook, or punchmark on the left edge of the 555. Pin 1 will be in the lower left where the dot is. Pin 8 will be directly across from pin 1. The pins are numbered counterclockwise when looking at the top of the chip.
not if that's a stripe alond the lendth with minus symbola all over it that marks the negative terminal.
if you're meaning a groove at one end of a coaxial capacitor (one lead each end) then yeah the groove end is positive
fairly reliable.
looking at your picture it looks like you have the 555 in with the pins like this: (I can't see it clearly, but given the other wiring that makes the most sesne)
4 3 2 1 | o| | SSSW7( | | 5 6 7 8
This is typically called "upside down" as the writing on the chip will be upside down. there's no rule against doing this but is is considered unconventional.
I'm assuming The positive supply is the top of the page, (by the red LED)
The electrolytic capacitor is backwards. pin 4 should be connected to the positive supply. the LEDs are backwards too.
Oh? Look to the internal schematic of the 555 they show a string of three 5K resistors to make the 1/3 and 2/3 dividers any DMM and most analog meters should be fine there.
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I made a bunch of mistakes and now my circuit looks much better and actually works. I set discharge resistance to be low, and added potentionmeters so that I could change its timing. Now I have a strobe timer. Cool.
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