The 2 ways to make mark & space equal on a 555 astable circu

[Adam Funk]

<http://www.electronics-tutorials.ws/waveforms/555_oscillator.html>

From this link & other places, I see there are (at least) 2 ways to
make the 555 astable circuit produce a square wave with a 50% duty
cycle:

* putting 2 diodes into the circuit & using the same resistance
from Vcc to discharge as from discharge to trigger & threshold, as
shown in the "Improved 555 Oscillator Duty Cycle"

* ignoring the discharge pin as shown in "50% Duty Cycle Astable
Oscillator"

Is there ever any advantage to using the first version (with more
components)?

Thanks.

 

[Jasen Betts]

On 2015-06-25, Adam Funk <a24061@ducksburg.com> wrote:

http://www.electronics-tutorials.ws/waveforms/555_oscillator.html

From this link & other places, I see there are (at least) 2 ways to
make the 555 astable circuit produce a square wave with a 50% duty
cycle:

* putting 2 diodes into the circuit & using the same resistance
from Vcc to discharge as from discharge to trigger & threshold, as
shown in the "Improved 555 Oscillator Duty Cycle"

* ignoring the discharge pin as shown in "50% Duty Cycle Astable
Oscillator"

Is there ever any advantage to using the first version (with more
components)?

Second version only works correctly with CMOS 555s it comes comes
close-ish with regular 555s but comes out a bit low. If the supply
voltage is fixed this can be corrected by tweaking with an additional
resistor.

--
umop apisdn

 

[Michael Black]

On Thu, 25 Jun 2015, Adam Funk wrote:

http://www.electronics-tutorials.ws/waveforms/555_oscillator.html

From this link & other places, I see there are (at least) 2 ways to
make the 555 astable circuit produce a square wave with a 50% duty
cycle:

* putting 2 diodes into the circuit & using the same resistance
from Vcc to discharge as from discharge to trigger & threshold, as
shown in the "Improved 555 Oscillator Duty Cycle"

* ignoring the discharge pin as shown in "50% Duty Cycle Astable
Oscillator"

Is there ever any advantage to using the first version (with more
components)?

The way I remember it, the diode scheme came from Signetics, so that
appeared first.

The one where the capacitor is charged and discharged via pin 3 and a
single resistor, that was in "Engineer's Notebook" or "Designer's
Casebook" (or maybe I have those jumbled) in "Electronics" magazine, just
a circuit and a small description, sometime in the early seventies.

I've always used that circuit with the resistor from pin 3 since I saw
that bit in "Electronics", it's just so much simpler unless you need
something more complicated.

On the other hand, some have pointed out that the original 555 isn't
perfect in this regard, the scheme works better with the CMOS 555. So that might
factor in if you had some very specific need for exact 50% duty cycle.
The original circuit in "Electronics" was for the original 555, though if
I remember properly, they also had a pullup resistor on pin 3 (but I've
never bothered with that).

I would point out that if someone needs an exact 50% duty cycle, it's just
as easy to put the signal through a divider to get that 50%, and digital
is often simpler than analog.

Michael

 

[Jim Thompson]

On Thu, 25 Jun 2015 11:40:03 +0100, Adam Funk <a24061@ducksburg.com>
wrote:

http://www.electronics-tutorials.ws/waveforms/555_oscillator.html

From this link & other places, I see there are (at least) 2 ways to
make the 555 astable circuit produce a square wave with a 50% duty
cycle:

* putting 2 diodes into the circuit & using the same resistance
from Vcc to discharge as from discharge to trigger & threshold, as
shown in the "Improved 555 Oscillator Duty Cycle"

* ignoring the discharge pin as shown in "50% Duty Cycle Astable
Oscillator"

Is there ever any advantage to using the first version (with more
components)?

Thanks.

There's an even easier way (at least for the CMOS version). The
charge/discharge resistor is driven from the output pin.

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Tim Wescott]

On Thu, 25 Jun 2015 11:40:03 +0100, Adam Funk wrote:

http://www.electronics-tutorials.ws/waveforms/555_oscillator.html

From this link & other places, I see there are (at least) 2 ways to make
the 555 astable circuit produce a square wave with a 50% duty cycle:

* putting 2 diodes into the circuit & using the same resistance
from Vcc to discharge as from discharge to trigger & threshold, as
shown in the "Improved 555 Oscillator Duty Cycle"

* ignoring the discharge pin as shown in "50% Duty Cycle Astable
Oscillator"

Is there ever any advantage to using the first version (with more
components)?

Thanks.

As pointed out, the second way requires a CMOS "555".

The diode method lets you set any arbitrary duty cycle, not just 50%.

--
www.wescottdesign.com

 

[Jim Thompson]

On Thu, 25 Jun 2015 12:16:49 -0500, Tim Wescott <tim@seemywebsite.com>
wrote:

On Thu, 25 Jun 2015 11:40:03 +0100, Adam Funk wrote:

http://www.electronics-tutorials.ws/waveforms/555_oscillator.html

From this link & other places, I see there are (at least) 2 ways to make
the 555 astable circuit produce a square wave with a 50% duty cycle:

* putting 2 diodes into the circuit & using the same resistance
from Vcc to discharge as from discharge to trigger & threshold, as
shown in the "Improved 555 Oscillator Duty Cycle"

* ignoring the discharge pin as shown in "50% Duty Cycle Astable
Oscillator"

Is there ever any advantage to using the first version (with more
components)?

Thanks.

As pointed out, the second way requires a CMOS "555".

The diode method lets you set any arbitrary duty cycle, not just 50%.

For frequency _and_ duty-cycle control see Freq_Duty_555.pdf on the
S.E.D/Schematics Page of my website.

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[whit3rd]

On Thursday, June 25, 2015 at 6:04:01 AM UTC-7, Michael Black wrote:

I would point out that if someone needs an exact 50% duty cycle, it's just
as easy to put the signal through a divider to get that 50%, and digital
is often simpler than analog.

The CD4541, or ICM7242, has the oscillator and divider(s) all wired into one chip.

 

[M Philbrook]

In article <3d2t5cxn8h.ln2@news.ducksburg.com>, a24061@ducksburg.com
says...

http://www.electronics-tutorials.ws/waveforms/555_oscillator.html

From this link & other places, I see there are (at least) 2 ways to
make the 555 astable circuit produce a square wave with a 50% duty
cycle:

* putting 2 diodes into the circuit & using the same resistance
from Vcc to discharge as from discharge to trigger & threshold, as
shown in the "Improved 555 Oscillator Duty Cycle"

* ignoring the discharge pin as shown in "50% Duty Cycle Astable
Oscillator"

Is there ever any advantage to using the first version (with more
components)?

Thanks.

sure.
tie the trigger and threshold together with a R to common and a Cap
from output to this same node.
This will give you a square wave that is close enough.

Jamie

 

[Jasen Betts]

On 2015-06-25, M Philbrook <jamie_ka1lpa@charter.net> wrote:

sure.
tie the trigger and threshold together with a R to common and a Cap
from output to this same node.
This will give you a square wave that is close enough.

sure, if you don't care about the frequency.
else swap C and R

--
umop apisdn

 

[Michael Black]

On Thu, 25 Jun 2015, whit3rd wrote:

On Thursday, June 25, 2015 at 6:04:01 AM UTC-7, Michael Black wrote:

I would point out that if someone needs an exact 50% duty cycle, it's just
as easy to put the signal through a divider to get that 50%, and digital
is often simpler than analog.

The CD4541, or ICM7242, has the oscillator and divider(s) all wired into one chip.

And Exar or someone used to have a timer that was probably a 555 followed
by about a 7 stage ripple counter, for really long time delays.

Michael

 

[John Fields]

On 26 Jun 2015 21:56:48 GMT, Jasen Betts <jasen@xnet.co.nz> wrote:

On 2015-06-25, M Philbrook <jamie_ka1lpa@charter.net> wrote:

sure.
tie the trigger and threshold together with a R to common and a Cap
from output to this same node.
This will give you a square wave that is close enough.

sure, if you don't care about the frequency.
else swap C and R

---
Umm...

With the RC wired the way M Philbrook described, the output will
always be a square wave regardless of frequency, and frequency can
be changed by changing the values of either R, or C, or both.

John Fields

 

[Michael A. Terrell]

Michael Black wrote:

On Thu, 25 Jun 2015, whit3rd wrote:

On Thursday, June 25, 2015 at 6:04:01 AM UTC-7, Michael Black wrote:

I would point out that if someone needs an exact 50% duty cycle, it's just
as easy to put the signal through a divider to get that 50%, and digital
is often simpler than analog.

The CD4541, or ICM7242, has the oscillator and divider(s) all wired into one chip.

And Exar or someone used to have a timer that was probably a 555 followed
by about a 7 stage ripple counter, for really long time delays.

Michael

The CD4020?

 

[Jasen Betts]

On 2015-06-27, Michael A. Terrell <mike.terrell@earthlink.net> wrote:

Michael Black wrote:

On Thu, 25 Jun 2015, whit3rd wrote:

On Thursday, June 25, 2015 at 6:04:01 AM UTC-7, Michael Black wrote:

I would point out that if someone needs an exact 50% duty cycle, it's just
as easy to put the signal through a divider to get that 50%, and digital
is often simpler than analog.

The CD4541, or ICM7242, has the oscillator and divider(s) all wired into one chip.

And Exar or someone used to have a timer that was probably a 555 followed
by about a 7 stage ripple counter, for really long time delays.

Michael

The CD4020?

CD4020 is just a ripple coubnter, CD4060 is the one with the in-built
oscillator, it has a 14 stage divider but not all stages are tapped.

Among other applications it's used for the timer in cheap toasters.
(not that i've ever _repaired_ a cheap toaster)

--
umop apisdn

 

[Michael Black]

On Sat, 27 Jun 2015, Michael A. Terrell wrote:

Michael Black wrote:

On Thu, 25 Jun 2015, whit3rd wrote:

On Thursday, June 25, 2015 at 6:04:01 AM UTC-7, Michael Black wrote:

I would point out that if someone needs an exact 50% duty cycle, it's just
as easy to put the signal through a divider to get that 50%, and digital
is often simpler than analog.

The CD4541, or ICM7242, has the oscillator and divider(s) all wired into one chip.

And Exar or someone used to have a timer that was probably a 555 followed
by about a 7 stage ripple counter, for really long time delays.

Michael

The CD4020?

No, the xr2242 (I couldn't remember the exact number earlier, so I didn't
list it, now I had to check).

It's been a while since I looked at the datasheet, but if I recall, it was
a bit more than an oscillator and divider chain, there was some feedback
point so the divider output could stop the oscillator or something.

Michael

 

[Michael Black]

On Sat, 27 Jun 2015, Jasen Betts wrote:

On 2015-06-27, Michael A. Terrell <mike.terrell@earthlink.net> wrote:

Michael Black wrote:

On Thu, 25 Jun 2015, whit3rd wrote:

On Thursday, June 25, 2015 at 6:04:01 AM UTC-7, Michael Black wrote:

I would point out that if someone needs an exact 50% duty cycle, it's just
as easy to put the signal through a divider to get that 50%, and digital
is often simpler than analog.

The CD4541, or ICM7242, has the oscillator and divider(s) all wired into one chip.

And Exar or someone used to have a timer that was probably a 555 followed
by about a 7 stage ripple counter, for really long time delays.

Michael

The CD4020?

CD4020 is just a ripple coubnter, CD4060 is the one with the in-built
oscillator, it has a 14 stage divider but not all stages are tapped.

Among other applications it's used for the timer in cheap toasters.
(not that i've ever _repaired_ a cheap toaster)

Do they make expensive ones now?

I opened at least one, all I saw was an 8pin DIP, I assumed it was a
microcontroller of some sort, kind of overkill, but probably simpler than
the timer.

Michael

 

[Michael A. Terrell]

Michael Black wrote:

On Sat, 27 Jun 2015, Michael A. Terrell wrote:


Michael Black wrote:

On Thu, 25 Jun 2015, whit3rd wrote:

On Thursday, June 25, 2015 at 6:04:01 AM UTC-7, Michael Black wrote:

I would point out that if someone needs an exact 50% duty cycle, it's just
as easy to put the signal through a divider to get that 50%, and digital
is often simpler than analog.

The CD4541, or ICM7242, has the oscillator and divider(s) all wired into one chip.

And Exar or someone used to have a timer that was probably a 555 followed
by about a 7 stage ripple counter, for really long time delays.

Michael

The CD4020?

No, the xr2242 (I couldn't remember the exact number earlier, so I didn't
list it, now I had to check).

It's been a while since I looked at the datasheet, but if I recall, it was
a bit more than an oscillator and divider chain, there was some feedback
point so the divider output could stop the oscillator or something.

Michael

I haven't used the 4020 since the '80s, but I remembered that it was
a multi stage ripple counter.

 

[Michael Black]

On Sat, 27 Jun 2015, Michael A. Terrell wrote:

Michael Black wrote:

On Sat, 27 Jun 2015, Michael A. Terrell wrote:


Michael Black wrote:

On Thu, 25 Jun 2015, whit3rd wrote:

On Thursday, June 25, 2015 at 6:04:01 AM UTC-7, Michael Black wrote:

I would point out that if someone needs an exact 50% duty cycle, it's just
as easy to put the signal through a divider to get that 50%, and digital
is often simpler than analog.

The CD4541, or ICM7242, has the oscillator and divider(s) all wired into one chip.

And Exar or someone used to have a timer that was probably a 555 followed
by about a 7 stage ripple counter, for really long time delays.

Michael

The CD4020?

No, the xr2242 (I couldn't remember the exact number earlier, so I didn't
list it, now I had to check).

It's been a while since I looked at the datasheet, but if I recall, it was
a bit more than an oscillator and divider chain, there was some feedback
point so the divider output could stop the oscillator or something.

Michael


I haven't used the 4020 since the '80s, but I remembered that it was
a multi stage ripple counter.

Yes it is. But some of those long ripple counters didn't have all the
outputs available, though I can't remember if that was the 4020 or the
4060. And as someone pointed out, it is the 4060 that had the built in
oscillator.

I think I missed something there. I bet the ICM7242 that somebody
mentioned is just the XR timer I was thinking of but from a different
manufacturer and hence a variant on the number.

The XR had some feedback, so if that output changed states, you could stop
the oscillator, or something like that. So it was a more integrated
concept than just an oscillator with a divider chain.

Michael

 

[Phil Allison]

John Fields wrote:

Maynard Philbrook

tie the trigger and threshold together with a R to common and a Cap
from output to this same node.
This will give you a square wave that is close enough.


With the RC wired the way M Philbrook described, the output will
always be a square wave regardless of frequency, and frequency can
be changed by changing the values of either R, or C, or both.

** Maynard's wrong connection does not work.

All it creates is high frequency squegging or nothing.



.... Phil

 

[John Fields]

On Sat, 27 Jun 2015 22:56:59 -0700 (PDT), Phil Allison
<pallison49@gmail.com> wrote:

John Fields wrote:

Maynard Philbrook

tie the trigger and threshold together with a R to common and a Cap
from output to this same node.
This will give you a square wave that is close enough.


With the RC wired the way M Philbrook described, the output will
always be a square wave regardless of frequency, and frequency can
be changed by changing the values of either R, or C, or both.


** Maynard's wrong connection does not work.

All it creates is high frequency squegging or nothing.



... Phil

---
You're right; can't imagine what I was thinking...

Thanks for the reality check.

John Fields

 

[M Philbrook]

In article <35avoa183rm86enfsak3e80s7mvaj939k6@4ax.com>,
jfields@austininstruments.com says...

On Sat, 27 Jun 2015 22:56:59 -0700 (PDT), Phil Allison
pallison49@gmail.com> wrote:

John Fields wrote:

Maynard Philbrook

tie the trigger and threshold together with a R to common and a Cap
from output to this same node.
This will give you a square wave that is close enough.


With the RC wired the way M Philbrook described, the output will
always be a square wave regardless of frequency, and frequency can
be changed by changing the values of either R, or C, or both.


** Maynard's wrong connection does not work.

All it creates is high frequency squegging or nothing.



... Phil

---
You're right; can't imagine what I was thinking...

Thanks for the reality check.

John Fields

Oh excuse me for not looking closer, the connects are correct, I
just had the two components switched around.

Either way, they both produce 50% duty cycle. One rounded corners at
high freq max to the chip operatin and the other square at RC freq..

I do make misakes at times. At least I can admit to it.

Jamie