NE555 Monostable Problem

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Suraj143

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I need roughly 1Sec delay.

T=1.1*R*C
T=1.1*100K*470uF
T=52Sec

The problem is after triggered the output lamp never gets off
sometimes it gets off taking very long time.

How to avoid this & make a smooth run?
 
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Suraj143 said:
I need roughly 1Sec delay.

T=1.1*R*C
T=1.1*100K*470uF
T=52Sec

The problem is after triggered the output lamp never gets off
sometimes it gets off taking very long time.

How to avoid this & make a smooth run?
Click to expand...

Hi Suraj,

The timing components will give a 52Sec ON time, but you say you want a 1 Sec delay.??

Whats the rating of the lamp.?
 
The switch must be momentary. The output will never reset if pin 2 stays low.
The datasheet of the NE555 from Philips shows how to capacitor-couple a continuous switch closure to work.
The datasheet also shows that a 555 needs a supply bypass capacitor close to the IC.
 
sorry for confusing guys I need a 1 minute delay not 1 sec.

Lamp is 20mA.
 
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20 mA, I Presume your using an LED?
That is OK.

And a 120K resistor and a 470uF cap is 62 Seconds.
However, Electrolytic Caps usually have High Leakage, and that can result in it Not operating as expected.

Electrolytic caps also have Very Poor Tollerances.
So Electrolytic caps are typically + or - 20% of rated value. Sometimes even WORSE.

A Tantalum cap would be Better for tollerance and leakage.
So I would recomment a 1.2 Meg Resistor and a 47uf Tantalum.
 
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A very good reply that's what I expected.

but I read some articles,they say due to leakage current in electrolytic caps use a bigger value cap & a smaller value resister.

I'll find some tantalum but those are very hard to find.Even some shopkeepers never heard those
 
but I read some articles,they say due to leakage current in electrolytic caps use a bigger value cap & a smaller value resister.

TRUE, But 100K is NOT a Small Value.
And your trying for a rather Lone Time for a 555.

LOOK HERE:
https://www.goldmine-elec-products.com/prodinfo.asp?number=G16384

Alternately I have a 22 uF Tantalum that could be used with a Higher value Resistor, But shipping it to you is probably expensive.
 
Guys here I cannot find any Tantalum caps.We have only chinese caps.

I used 47uF with 1.2Mohms but the output never turn off.

I changed the cap to 33uF with 1.2M ohms then the LED turned off after 60 seconds.But according to formula it should turn off @ 42 seconds.

Is there anyway to make a monostable 1minute delay with commonly available parts?

I just noticed above 33uF capacitor the output never turned off.
 
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Your Caps have Too Much Leakage.

Possibly try a 10 uF cap and a 5.6 Meg Resistor. (for 61 Seconds)

Where is "South Mald Isld"?

Failing Success with this, Possibly I could Mail you a 10 uf Tantalum cap and the 5M6 resistor.
 
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Tantalum capacitors are "commonly available parts" everywhere except where you are.

High quality electrolytic capacitors do not leak current badly like your cheap ones.
 
If you want a consistent 60sec period it would be better to avoid electrolytic caps altogether. That would probably mean using e.g. a CD4060, or using the 555 to drive a counting IC (e.g. CD4024).
 
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