Hmm what's wrong? - Electronic Circuits Projects Diagrams Free

daviddoria · 26th March 2003, 04:02 PM

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 · 26th March 2003, 04:06 PM

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 · 26th March 2003, 04:40 PM

ok now both resistors are 100k

what would cause it to stop after 1 flash??

Gene · 26th March 2003, 04:53 PM

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

**kinjalgp** · 26th March 2003, 04:53 PM

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 · 26th March 2003, 04:59 PM

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 · 26th March 2003, 05:09 PM

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

pebe · 26th March 2003, 06:03 PM

Quote:

Originally Posted by bogdanfirst

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

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 · 26th March 2003, 06:41 PM

yes, i confused it with somehting else

daviddoria · 27th March 2003, 01:31 AM

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 · 27th March 2003, 07:24 PM

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

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26th March 2003, 04:02 PM	(permalink)
daviddoria	Hmm what's wrong? 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? __________________ thanks, david

26th March 2003, 04:06 PM	(permalink)
bogdanfirst	as far as i know the resistance from +V(pin8) to pin 7 must be greater than 5K. try a greater value for it.

26th March 2003, 04:40 PM	(permalink)
daviddoria	ok now both resistors are 100k what would cause it to stop after 1 flash?? __________________ thanks, david

26th March 2003, 04:53 PM	(permalink)
Gene	The wire coming from pin #7 is wrong - it should connect to 2 resistors instead of one.

26th March 2003, 04:53 PM	(permalink)
kinjalgp	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. __________________ "There is no way to peace, peace is the way!"

26th March 2003, 04:59 PM	(permalink)
daviddoria	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.... __________________ thanks, david

26th March 2003, 05:09 PM	(permalink)
bogdanfirst	the cap on pin 5 is for frequency compensation.... use it only on highter frequencies

26th March 2003, 06:41 PM	(permalink)
bogdanfirst	yes, i confused it with somehting else

27th March 2003, 01:31 AM	(permalink)
daviddoria	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. __________________ thanks, david

27th March 2003, 07:24 PM	(permalink)
bogdanfirst	well that is what they say in the datasheet......