Is a 555 a reliable low frequency oscillator?

[Joe]

I am trying to build a timer circuit to turn on a relay for 60 seconds
every 1, 2, or 4 hours. I was planning on using a 555 astable running at
approximately 1 pulse every 3.5 seconds connecting that output to the cd
4020 clock input , and then using a dip switch to take the outputs from the
cd 4020 at the 1024, 2048, or 4096 output for my 1hr, 2hr, or 4hrs (plus or
minus a few minutes). This signal would trigger a oneshot to turn the relay
on for 60 seconds. My plan was to also reset the 4020 at this same time
using the signal from the oneshot.

I am wondering if the 555 is a good choice at such a low frequency (0.28
Hz). It can supposedly supply a frequency as low as 0.1Hz according to my
TTL cookbook.

TIA,
Joe

 

[John Popelish]

Joe wrote:

I am trying to build a timer circuit to turn on a relay for 60 seconds
every 1, 2, or 4 hours. I was planning on using a 555 astable running at
approximately 1 pulse every 3.5 seconds connecting that output to the cd
4020 clock input , and then using a dip switch to take the outputs from the
cd 4020 at the 1024, 2048, or 4096 output for my 1hr, 2hr, or 4hrs (plus or
minus a few minutes). This signal would trigger a oneshot to turn the relay
on for 60 seconds. My plan was to also reset the 4020 at this same time
using the signal from the oneshot.

I am wondering if the 555 is a good choice at such a low frequency (0.28
Hz). It can supposedly supply a frequency as low as 0.1Hz according to my
TTL cookbook.

TIA,
Joe

The 555 is probably plenty stable for this task, assuming you keep all
power supply spikes away from its reference (bypass pin 5 to pin 1 and
also tie your timing capacitor very close to pin 1). The reference is
what is compared to the capacitor voltage to determine time-out, and
these two need to be clean with respect to pin 1 if they are going to
be accurately compared.

I suggest you use a mylar or polypropylene timing capacitor, instead
of an electrolytic, and use the cmos version of the 555 (E.g.. LMC555)
to keep the comparator bias currents much lower than the capacitor
charging current. Its output is CMOS, which is a better match to the
CMOs counter.

The 555 has a slight glitch problem, that might double clock your
counter, occasionally, but you can cure this by putting a 10k resistor
between the 555 output and the clock input.

--
John Popelish

 

[Rich Grise]

"Joe" <nuisancewildlife@nospamearthlink.net> wrote in message news:<GVATa.18487$Mc.1409952@newsread1.prod.itd.earthlink.net>...

I am trying to build a timer circuit to turn on a relay for 60 seconds
every 1, 2, or 4 hours. I was planning on using a 555 astable running at
approximately 1 pulse every 3.5 seconds connecting that output to the cd
4020 clock input , and then using a dip switch to take the outputs from the
cd 4020 at the 1024, 2048, or 4096 output for my 1hr, 2hr, or 4hrs (plus or
minus a few minutes). This signal would trigger a oneshot to turn the relay
on for 60 seconds. My plan was to also reset the 4020 at this same time
using the signal from the oneshot.

I am wondering if the 555 is a good choice at such a low frequency (0.28
Hz). It can supposedly supply a frequency as low as 0.1Hz according to my
TTL cookbook.

TIA,
Joe

According to National Semi's LMC555 data sheet (you'll have to search
it out - I don't have the URL handy, I've downloaded the PDF.), you
can get a 100 sec delay with 10M and 10 uF. In astable mode, the
chart goes to .1 Hz at 10M and 1 uF.

So use the CMOS one, and use good, low-leakage caps.

Good Luck!
Rich

 

[Joe]

"Rich Grise" <richardgrise@yahoo.com> wrote in message
news:3df9fd6c.0307231531.62616583@posting.google.com...

"Joe" <nuisancewildlife@nospamearthlink.net> wrote in message
news:<GVATa.18487$Mc.1409952@newsread1.prod.itd.earthlink.net>...
I am trying to build a timer circuit to turn on a relay for 60 seconds
every 1, 2, or 4 hours. I was planning on using a 555 astable running at
approximately 1 pulse every 3.5 seconds connecting that output to the cd
4020 clock input , and then using a dip switch to take the outputs from
the
cd 4020 at the 1024, 2048, or 4096 output for my 1hr, 2hr, or 4hrs (plus
or
minus a few minutes). This signal would trigger a oneshot to turn the
relay
on for 60 seconds. My plan was to also reset the 4020 at this same time
using the signal from the oneshot.

I am wondering if the 555 is a good choice at such a low frequency (0.28
Hz). It can supposedly supply a frequency as low as 0.1Hz according to
my
TTL cookbook.

TIA,
Joe

According to National Semi's LMC555 data sheet (you'll have to search
it out - I don't have the URL handy, I've downloaded the PDF.), you
can get a 100 sec delay with 10M and 10 uF. In astable mode, the
chart goes to .1 Hz at 10M and 1 uF.

So use the CMOS one, and use good, low-leakage caps.

Good Luck!
Rich

Thanks for the help, I am very grateful. I also appreciate learning about
the microcontrollers. Thank you for the links. Maybe as my abilities
improve, I will make the transition to them.

Anyway, off to the breadboard!

Joe

 

[manuka]

Forget 555s - longer intervals pretty swampy ( due to electrolytic
cap. leakages etc )& their standby power is too high anyway- even for
the CMOS 7555 versions. Instead suggest the UK sourced PICAXE-08 =>
www.picaxe.com . The "08" is PIC12F629 based anyway, but has such high
level commands ( SLEEP, NAP, GOTO, WAIT etc ) that setting up hours
long repetitive delays is a breeze. Their SLEEP command exploits a low
power mode drawing just microAmps. Free editor & bubble gum cheap
chips ( start at a GBP1 pound !)Check also => www.picaxe.orcon.net.nz

 

[Joe]

"manuka" <manuka@orcon.net.nz> wrote in message
news:dd8572bb.0308021415.5cd6b954@posting.google.com...

Forget 555s - longer intervals pretty swampy ( due to electrolytic
cap. leakages etc )& their standby power is too high anyway- even for
the CMOS 7555 versions. Instead suggest the UK sourced PICAXE-08 =
www.picaxe.com . The "08" is PIC12F629 based anyway, but has such high
level commands ( SLEEP, NAP, GOTO, WAIT etc ) that setting up hours
long repetitive delays is a breeze. Their SLEEP command exploits a low
power mode drawing just microAmps. Free editor & bubble gum cheap
chips ( start at a GBP1 pound !)Check also => www.picaxe.orcon.net.nz

Thank you for the suggestions. I am just now getting back into this after
20+ years. I am still getting used to all this new technology. I have
successfully implemented the project referenced in the original subject line
using a 555, and also accomplished the same thing using a cd4060. The
original intent was to generate a frequency and turn a relay on for 60 sec
(not a long interval one shot) every 1,2 and 4 hrs. The project worked
nicely both ways. When I need to make the technological leap to
microcontrollers (maybe with my next project), I will. Someone else posted
some good links.

Thank you for your reply,
Joe

 

[Bill Bowden]

"Joe" <nuisancewildlife@nospamearthlink.net> wrote in message news:<VL_Wa.3462$kP6.737@newsread2.news.atl.earthlink.net>...

"manuka" <manuka@orcon.net.nz> wrote in message
news:dd8572bb.0308021415.5cd6b954@posting.google.com...
Forget 555s - longer intervals pretty swampy ( due to electrolytic
cap. leakages etc )& their standby power is too high anyway- even for
the CMOS 7555 versions. Instead suggest the UK sourced PICAXE-08 =
www.picaxe.com . The "08" is PIC12F629 based anyway, but has such high
level commands ( SLEEP, NAP, GOTO, WAIT etc ) that setting up hours
long repetitive delays is a breeze. Their SLEEP command exploits a low
power mode drawing just microAmps. Free editor & bubble gum cheap
chips ( start at a GBP1 pound !)Check also => www.picaxe.orcon.net.nz

Thank you for the suggestions. I am just now getting back into this after
20+ years. I am still getting used to all this new technology. I have
successfully implemented the project referenced in the original subject line
using a 555, and also accomplished the same thing using a cd4060. The
original intent was to generate a frequency and turn a relay on for 60 sec
(not a long interval one shot) every 1,2 and 4 hrs. The project worked
nicely both ways. When I need to make the technological leap to
microcontrollers (maybe with my next project), I will. Someone else posted
some good links.

Thank you for your reply,
Joe

I found a good tutorial on the PIC microcontrollers at:

http://www.mstracey.btinternet.co.uk/pictutorial/picmain.htm

It's mostly assemply language (35 instructions) which you can
write using IDE software from www.microchip.com. The IDE will
generate the hex code to load into the PIC. And there is a free
programmer schematic at http://www.nomad.ee/PIC/ (plus DOS software
PIC84V05.zip) which will load the hex file into the PIC from the
PC printer port. It's all free stuff except the micro.
The PIC16F628 is popular and has one 8 bit I/O port and another
4 bit I/O port and can be bought on e-bay for $2.68 each.

-Bill