Help with basic 555 timer circuit

[pranmala]

Hello, I am having trouble getting a very simple 555 timer circuit to
work. I have studied hard the documentation for the various pins and am

trying this simple circuit, but the o/p PIN3 stays high for just a
fraction of second when I take trigger input 2 low. The values of R or
C in the RC combination seem to have no bearing on the the pulse width.


The circuit I am working on is the first part of the '2 stage Time
delay circuit'.
I am giving the link to the image of the cicuit that I am using (with
due credit to rpaisley)


http://home.cogeco.ca/~rpaisley4/LM555.html#24


Instead of PIN3 of the first chip feeding the second chip, I have an
LED (with 1K resistor in serial going to -ve ). I have assembled the
circuit on a bread board. Thinking the chip is faulty, I had replaced
it twice. I also tried switching the capacitor from 100microfarad to
..001 microfarad. The resistors from 220K to 1 K. The time constant of
1.1 RC seem to have no bearing on my circuit.


Any help will be greatly appreciated.
Thanks !
pranmala

 

[Bill Bowden]

Hello, I am having trouble getting a very simple 555 timer circuit to
work. I have studied hard the documentation for the various pins and am

trying this simple circuit, but the o/p PIN3 stays high for just a
fraction of second when I take trigger input 2 low. The values of R or
C in the RC combination seem to have no bearing on the the pulse width.


The circuit I am working on is the first part of the '2 stage Time
delay circuit'.
I am giving the link to the image of the cicuit that I am using (with
due credit to rpaisley)


http://home.cogeco.ca/~rpaisley4/LM555.html#24


Instead of PIN3 of the first chip feeding the second chip, I have an
LED (with 1K resistor in serial going to -ve ). I have assembled the
circuit on a bread board. Thinking the chip is faulty, I had replaced
it twice. I also tried switching the capacitor from 100microfarad to
.001 microfarad. The resistors from 220K to 1 K. The time constant of
1.1 RC seem to have no bearing on my circuit.


Any help will be greatly appreciated.
Thanks !
pranmala

Sounds like you have the wrong R and C values. Changing the C value
from 100uF to .001uF will make the output time very short. Look closely
at the parts your using, and be sure they are the right value. 100uF
cap and 220K resistor should give you an output time of around 24
seconds.The 220K resistor will have color markings of red,red, and
yellow. The 100uF capacitor will have polarity markings of + and -.

-Bill

 

[[email protected]]

If this is your first 555 circuit, I recommend using the 555 Timer Lite
program to simulate the results of different component values.

http://www.schematica.com/555_Timer_design/555.htm

On to your problem. First of all, I'm not quite clear on what you are
doing with the circuit. It sounds like you are trying to use just the
left half of the schematic to blink and LED. Am I correct in this
assumption? If your purpose is to simply blink an LED, why not start
from a schematic designed to do such? There are many available online.

This page shows photos of a breadboard with a simple 555 timer circuit:

http://www.geocities.com/SiliconValley/2072/proj2.htm

Perhaps that will get you on your way.

Good luck,
Tavys

 

[Wayne Lundberg]

Great response!!!!