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problems with simple 555 timer

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kwirky

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Hey I'm new to the forums, thought maybe you people could help me:

Here's my circuit, produced by a program I downloaded:
**broken link removed**

resistor A is 5.6kohm and resistor B is 15kohm. the electrolytic capacitor is 100uF.

I'm driving it with a 5V 600mah power adapter. I've connected pin 3 to the + of an LED, then the - of the LED to grnd

now the 0.01uF capacitor I'm using is a 200V mica capacitor (103k). is this the wrong capacitor to use for the 0.01uF capacitor in that diagram? should I be using an electrolytic?

Also, the 555 timer doesn't have a notch to show which way is up. There is a printed IC number on the board though, do I orient it according to that?

what happens is my LED turns on, and stays on. indefinately. anyone able to help?
 
hi,
The 0.01uF capacitor is OK.

You say that there is no pin #1 ID, no notch, is there a small white dot or shallow circular indentation in the plastic case near pin #1, use a magnifier.

What freq are you expecting from pin #3 ?

Try a 10uF in place of the 100uF, the datasheet is showing with 20K [sum] and 100uF is outside spec???
 
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Frankly, I see nothing wrong with the program or values as presented. There must be some slight error in your hardware. I loaded your values into my 555 simulator and came up with similar results.

As a last resort, you can generally rely on the fact that pin 1 will be in the lower left corner when you are holding the chip so the labeling is read correctly.

Also, it is typical with 555's that the first cycle will tend to be a bit longer than normal. Be patient. A second and a half can be a long time when you are watching comething.
 
You need a 150R in series with the LED. It may be dragging the supply down as it will be trying to draw a very large current if there is no resistor.
 
Just noticed..... according to the color bands in your depiction, those are the wrong resistors in the timing circuit. Those look like a pair of 100K to these old eyes. I hope the actual resistors in circuit are correct.

Also, dch222 is correct. There should be a 220 or 330 resistor between pin 3 and the LED in order to reduce current to around 20 mA.
 
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hi allvol,

Also just spotted the resistors, the text boxes say 5K6, 15K0 ??
 
dch222 said:
You need a 150R in series with the LED. It may be dragging the supply down as it will be trying to draw a very large current if there is no resistor.
Good for you! With almost 5V supplied to the poor LED, the latter also won't last long!
 
maybe it has 100k resistors in the depiction, because the programmers were too lazy to make color changing resistors...
 
if you'll notice above each resistor value, the number 100, as in 100k

I think the help file for this application explains that is the 'range' or maximum resistance (10k, 100k, 1m, 10m). the color bands on the resistors indicate this range, rather than the actual value. why that is, I don't know. is it a bug or a feature?
 
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