false signals triggering 555 timer

[aha]

anybody knows something about this?
i got a good 7812 power supply with big capacitors and some small mkm ,
and pin 2 connected to + with a 10k resistor wich improved a lot,but not all
of the error triggers.

thanks.abe

--











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[Mark J.]

In news:40364def$0$2436$4a441750@news.euronet.nl (aha):

anybody knows something about this?
i got a good 7812 power supply with big capacitors and some small mkm ,
and pin 2 connected to + with a 10k resistor wich improved a lot,but
not all of the error triggers.

thanks.abe

Place a 100nF (0.1uF) low-ESR cap right next to the 555's power pins. This
should fix it. If not, is it the CMOS 555?

 

[loedown]

Hi All,
I seem to remember something about a 100nF between earth and pin
5, but it has been a long time since I played with a 555

Paul

 

[Bob Parker]

Yeah, you should do that and bypass the supply pins with a
disc/monolithic 100nF as the previous person said. 555s are notorious
for false triggering. I've had embarrassing first-hand experience in
an old Yellow Light car alarm which was based on them...

Bob


"loedown" <zero242@bigpond.net.au> wrote:

Hi All,
I seem to remember something about a 100nF between earth and pin
5, but it has been a long time since I played with a 555

Paul

 

[w_tom]

Each recommendation is addressing same problem - noise
entering mostly via ground pin / ground connections. For
example, that 7812 power supply with large output capacitor
still is not sufficient bypass filtering for 555 if large
capacitor is more than 20 cm (wire) from 555.

Remember, wire is not a conductor. Wire is another
electronic component which is why the 'how' of grounding
becomes so important and why a bypass capacitor (preferred is
ceramic or tantalum - material not size of this capacitor is
more important) from VCC to ground right at 555 pins may be
necessary.

Some of this is discussed in application notes for 555 from
either TI or National Semiconductor web sites (and others).

IC also requires typically 0.01 uf capacitor on pin (pin
name forgotten) so that noise on the internal (3 resistor)
divider is clean - no noise.

aha wrote:

anybody knows something about this?
i got a good 7812 power supply with big capacitors and some small
mkm , and pin 2 connected to + with a 10k resistor wich improved
a lot,but not all of the error triggers.

 

[aha]

"Mark J." <127.0.0.1> schreef in bericht
newsqKdnTbaQrDo8avdRVn-vA@buckeye-express.com...

In news:40364def$0$2436$4a441750@news.euronet.nl (aha):
anybody knows something about this?
i got a good 7812 power supply with big capacitors and some small mkm ,
and pin 2 connected to + with a 10k resistor wich improved a lot,but
not all of the error triggers.

thanks.abe


Place a 100nF (0.1uF) low-ESR cap right next to the 555's power pins.
This
should fix it. If not, is it the CMOS 555?

nope,ne555

 

[Mark J.]

In news:40370dd7$0$63127$a344fe98@news.wanadoo.nl (aha):

"Mark J." <127.0.0.1> schreef in bericht
newsqKdnTbaQrDo8avdRVn-vA@buckeye-express.com...
In news:40364def$0$2436$4a441750@news.euronet.nl (aha):
anybody knows something about this?
i got a good 7812 power supply with big capacitors and some small mkm
, and pin 2 connected to + with a 10k resistor wich improved a lot,but
not all of the error triggers.

thanks.abe


Place a 100nF (0.1uF) low-ESR cap right next to the 555's power pins.
This should fix it. If not, is it the CMOS 555?


nope,ne555

Try running it from a 9V battery.