Hmm what's wrong?

daviddoria

New Member

• Mar 26, 2003

• #1

Take a look at this:

http://www.bandtank.com/~calculusap/notworking.gif

the idea is just to continuously flash the light via astable multivibration (555 timer)

what it actually does is turn the light on once then turn off then do nothing....
hmmm

is the drawing wrong? or did i just do something wrong?

 

bogdanfirst

New Member

• Mar 26, 2003

• #2

as far as i know the resistance from +V(pin8) to pin 7 must be greater than 5K. try a greater value for it.

 

daviddoria

New Member

• Mar 26, 2003

• #3

ok now both resistors are 100k

what would cause it to stop after 1 flash??

 

Gene

New Member

• Mar 26, 2003

• #4

The wire coming from pin #7 is wrong - it should connect to 2 resistors instead of one.

 

kinjalgp

Active Member

• Mar 26, 2003

• #5

I think you have wired 555 in monostable mode or you are missing something. The circuit seems ok except that you have not connected a capacitor of 0.01uF between pin 5 and ground which prevents spurious triggering of 555 due to noise.

 

daviddoria

New Member

• Mar 26, 2003

• #6

hahaha i am retarded. i had R2 connected to 8 instead of 7.

sorry for bothering you with this sillyness

kinaljp, maybe i'm just lucky, but i've done several things like this without the cap on pin 5 and i've not seen a problem....

 

bogdanfirst

New Member

• Mar 26, 2003

• #7

the cap on pin 5 is for frequency compensation....
use it only on highter frequencies

 

P

pebe

Member

• Mar 26, 2003

• #8

bogdanfirst said:

the cap on pin 5 is for frequency compensation....
use it only on highter frequencies

Click to expand...

Pin 5 is made available so that you can externally modify (for a variety of reasons) the potential divider used by the two internal comparitors.

In almost all cases you don't need a capacitor there - you can leave it undecoupled.

 

bogdanfirst

New Member

• Mar 26, 2003

• #9

yes, i confused it with somehting else

 

daviddoria

New Member

• Mar 26, 2003

• #10

just for feedback: it seems to work with a 1k resistor. duno if its because of the tolerence that it is close enough to 5, or what the deal is. just letting you know.

 

bogdanfirst

New Member

• Mar 27, 2003

• #11

well that is what they say in the datasheet......