Help With My 555 Astable Circuit

  • Thread starter sl1solo76
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In summary: I was NEVER expecting anything to be wrong. I was just hoping for some insight as to why i keep having this problem.In summary, the problem is that you are not following the instructions correctly and are not using the right parts.
  • #1
sl1solo76
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ive basically put in one try a day at this, and interchange about 3 IC's possibly thinking that's the problem, but when push comes to shove, i can't make a basic 555 astable circuit powering a LED. Recently all I've been able to get out of it is a glorified circuit to just make the LED light up, no fancy blinking involved.

I've taken all the circuit diagrams off the net (top google results), and have even tried a few off youtube, but no success... It may sound pathetic but some insight into what I am doing wrong would be greatly appreciated. Heres a picture of my most recent disaster on a breadboard-

http://img509.imageshack.us/img509/6361/1000038copysq3.jpg

*sigh*
 
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  • #2
Run a 1 K resistor between pin 7 and 8. There is nothing to charge the cap up the way you currently have it wired. Also, it wouldn't hurt to have a .1 uF cap between pin 1 and 8 for power supply decoupling. Pin 5 should probably have a .1 uF to ground.
-
Edit:
I just noticed a black wire that terminates somewhere under your 4.7k resistor. What is this doing here? Where does it go? I'm not sure it belongs there.
 
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  • #3
thats the sending wire to the 10k pot between pin 7 and the positive rail.. i put a 1k in where you had said and a 1uf from 5 to the ground, but the same thing happened, just that steady defeating green glow of the LED.
 
  • #4
I'm not sure where you have the pot wired to. Is it to pin 6 or 7? It should be wired to pin Not sure what you have the 10k pot set at, but typically when a 555 is wired astable and you want a duty cycle close to 50%, a resistor is put between pin 7 and the positive supply rail. The size of this resistor should be quite a lot smaller than the main resistor that goes between pin 7 and 6. (Like 10 times less) However, you need to be careful that you don't get the resistor so small that too much current flows through it into pin 7. Pin 7 is grounded via a transistor inside when the output of the 555 is low. So naturally, to small of a resistance will cause excessive current to flow into pin 7. I wired a 555 a couple of nights ago very similarly to the way you have it wired. I wanted about 300 hertz out of mine, but that is irrelevant. It should work the same. Can you verify what the voltages are doing on some of the pins? Do you have a digital voltmeter?
 
  • #5
yeah i do, ill work on it and post what I am getting
 
  • #6
alright so I've got the same 4.7k between 6 and 7 and a 1k running from 7 to the ground rail. The voltage for each pin reads-

1-0v
2-6.56v
3-6.58v
4-6.59
5-6.56
6-6.59
7-6.61
8-6.61

Battery (power source)-6.61vdc

now what would cause that? sure doesn't look normal to me...
 
  • #7
You are correct, it does not look right. I'd pull out the IC and measure again.
 
  • #8
1-0
2-7.21
3-0
4-7.25
5-0.01
6-0
7-7.25
8-7.27

Battery voltage- 7.27v
 
  • #9
You obviously have a problem with the breadboard, have something wired wrong or made a mistake in your measurements. Pin 2 and pin 6 should have the exact same voltage since they are tied together with a wire and they definitely are different.
 
  • #10
yep, the breadboard is wacky. I triple-checked it and really can't understand how exactly that is happening.. might want to go find a new one tomorrow..

EDIT: with the quadruple-checking i discovered that the wire connecting them wasnt all the way in on the 7 side.
 
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  • #11
Why can't you just slide the IC down to a new part of the board and rewire? At least temporarily. Give you some confidence wouldn't it? Seems like you're tired of having this thing kick your arse.
 
  • #12
well it wasnt the board in that case, the wire just wasn't all the way down.

and yes, a middle-school bully cannot begin to compete with the devastating effect this is having on my self-esteem.
 
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  • #13
Aha! there it is! the blinking light that has given me my self-respect back!
i never thought id be that excited over a blinking light... Thanks a ton man..
 
  • #14
Glad to have helped. I remember back on my first job doing electronic troubleshooting I made a comment to my trainer on the second day of work: "Things are sometimes not what they seem." He replied: "Things are NEVER as they seem." I will always remember that comment. In this case would you have expected to have a faulty wire/socket? You were most likely expecting that is was a mis-wire or faulty IC.
 

Related to Help With My 555 Astable Circuit

1. How does the 555 astable circuit work?

The 555 astable circuit is a type of multivibrator that produces a continuous square wave output. It works by using two resistors and one capacitor to create a feedback loop that controls the charging and discharging of the capacitor, resulting in a continuous oscillation of the output signal.

2. What components do I need for a 555 astable circuit?

To build a 555 astable circuit, you will need a 555 timer IC, two resistors, one capacitor, and a power supply. The values of the resistors and capacitor will determine the frequency and duty cycle of the output signal.

3. How do I calculate the frequency and duty cycle of the 555 astable circuit?

The frequency and duty cycle of the 555 astable circuit can be calculated using the following formulas:

Frequency (Hz) = 1.44 / ((R1 + 2R2) * C)

Duty Cycle (%) = (R1 + R2) / (R1 + 2R2) * 100

4. Can I adjust the frequency and duty cycle of the 555 astable circuit?

Yes, the frequency and duty cycle of the 555 astable circuit can be adjusted by changing the values of the resistors and capacitor. Increasing the values of the resistors will decrease the frequency and duty cycle, while increasing the value of the capacitor will increase the frequency and duty cycle.

5. How can I troubleshoot my 555 astable circuit if it is not working properly?

If your 555 astable circuit is not working properly, first check all of the connections and ensure that the components are correctly placed. You can also use a multimeter to check the values of the resistors and capacitor. If the values are not within the expected range, replace the components. If the circuit still does not work, there may be an issue with the 555 timer IC itself and it may need to be replaced.

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