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Variable duty cycle and frequency with a 555

C

captoro

Jan 1, 1970
0
Hello,

I'm on a quest here.
I am trying to find a circuit with a 555 timer that can both independently control the frequency and duty cycle(1% to 99%).
Most circuit I find is either or, A few was actually what I thought i needed but when completing the circuit, I found that when varying the frequency.. the duty cycle was also changing !! or vice versa.
I know with a LM393, (and I have that circuit) it is possible. but it is not fast enough. I can see on the scope that the 555 pulse starts to deteriorates 2.5us while the lm393 starts about at 100us
thanks for the help

ken
 
S

Spehro Pefhany

Jan 1, 1970
0
Hello,

I'm on a quest here.
I am trying to find a circuit with a 555 timer that can both independently control the frequency and duty cycle(1% to 99%).
Most circuit I find is either or, A few was actually what I thought i needed but when completing the circuit, I found that when varying the frequency.. the duty cycle was also changing !! or vice versa.
I know with a LM393, (and I have that circuit) it is possible. but it is not fast enough. I can see on the scope that the 555 pulse starts to deteriorates 2.5us while the lm393 starts about at 100us
thanks for the help

ken

Since you seem to be operating at relatively high frequencies, you
could alter the duty cycle with a pot and diodes and use a variable
capacitor to change the frequency.

You could also do it with a microcontroller with appropriate
peripherals on-chip (ADC inputs and a suitable timing peripheral)
 
C

captoro

Jan 1, 1970
0
Hello,



I'm on a quest here.

I am trying to find a circuit with a 555 timer that can both independently control the frequency and duty cycle(1% to 99%).

Most circuit I find is either or, A few was actually what I thought i needed but when completing the circuit, I found that when varying the frequency.. the duty cycle was also changing !! or vice versa.

I know with a LM393, (and I have that circuit) it is possible. but it is not fast enough. I can see on the scope that the 555 pulse starts to deteriorates 2.5us while the lm393 starts about at 100us

thanks for the help



ken

HI,

With further testing today I found that with Pic chip i was able to get better rise and fall time. I am not looking for high frequency, just fast risetime. The Pic chip starts to deteriorate at 2.5us and the 555 chip at 50us... now i'm thinking maybe there is something else faster then that !!

Ken
 
With further testing today I found that with Pic chip i was able to get better rise and fall time. I am not looking for high frequency, just fast rise time. The Pic chip starts to deteriorate at 2.5us and the 555 chip at 50us... now i'm thinking maybe there is something else faster then that !!

Which PIC? PIC32MX can toggle I/O at 80MHz (12ns cycle) with rise and falltime of 5ns.
 
J

Jamie

Jan 1, 1970
0
captoro said:
Hello,

I'm on a quest here.
I am trying to find a circuit with a 555 timer that can both independently control the frequency and duty cycle(1% to 99%).
Most circuit I find is either or, A few was actually what I thought i needed but when completing the circuit, I found that when varying the frequency.. the duty cycle was also changing !! or vice versa.
I know with a LM393, (and I have that circuit) it is possible. but it is not fast enough. I can see on the scope that the 555 pulse starts to deteriorates 2.5us while the lm393 starts about at 100us
thanks for the help

ken

Single digit ns comparator example
http://www.ti.com/lit/ds/sbos321d/sbos321d.pdf

You can do both the triangle oscillator and comparator with
the dual version of that..

THat is just an example, there are many that can do the low ns
time.

Jamie
 
M

mike

Jan 1, 1970
0
Single digit ns comparator example
http://www.ti.com/lit/ds/sbos321d/sbos321d.pdf

You can do both the triangle oscillator and comparator with
the dual version of that..

THat is just an example, there are many that can do the low ns
time.

Jamie
When you personally applied this part to the task, how did you manage
the reliable 1% and 99% duty factors with low jitter?
And how did you compensate for the delay through the part?

I used to design pulse/function generators for a living, so be
as technical as necessary.
 
B

Bill Sloman

Jan 1, 1970
0
I'm on a quest here.

I am trying to find a circuit with a 555 timer that can both independently control the frequency and duty cycle(1% to 99%).

Most circuit I find is either or, A few was actually what I thought i needed but when completing the circuit, I found that when varying the frequency.. the duty cycle was also changing !! or vice versa.

I know with a LM393, (and I have that circuit) it is possible. but it is not fast enough. I can see on the scope that the 555 pulse starts to deteriorates 2.5us while the lm393 starts about at 100us

This is an ill-conceived quest. If you want independent control of frequency and duty cycle, use a pair of counters, one dividing a high frequency clock - to determine your repetition frequency - from (say) falling edge to falling edge - and the other to determine where the intervening (say) rising edge appears.

If you used a 200MHz clock generator (which you can buy, off the shelf - Farnell has eleven in stock, several of them for about $A10 each in small quantities) and a pair of 20-bit counters in programmable logic device you'd be able to get down to 200Hz.

You'd have to limit your maximum frequency to 2MHz to be able to have a 1%/99% range on duty cycle would limit your maximum frequency to 20MHz, but the edge speeds would be fine.

If you went for ECLinPS counters, you could use the MC100EP195 delay generator to get finer positioning of the intermediate edge.

http://www.onsemi.com/pub_link/Collateral/MC10EP195-D.PDF

That provides up to 10nsec of delay, allowing you to drop back to a 100MHz oscillator programmable in roughly 10psec increments. The delay is depressingly temperature dependent (see figure 4) but if you were serious you couldset up and auto-calibration procedure where you set up a fast repetition rate waveform and measure it's DC contents as a function of the mark-to-space ratio set up by the delays in the MC100EP195. You'd need a 12-bit A/D converter or better, and a decent low pass filter in front of it but there's nothing complicated involved, and you can re-calibrate in few tens of milliseconds if you do it right.
 
S

Spehro Pefhany

Jan 1, 1970
0
The edges out of a pic should be nanoseconds, not microseconds. Is your scope
OK?

If one were to load it directly with a reasonably hefty MOSFET gate,
it could easily degrade to microseconds. Maybe 100-200nC would do it.

A driver circuit (a couple BJTs or a chip) would take care of it, were
that to be the case.


Best regards,
Spehro Pefhany
 
Hello,

I'm on a quest here.
I am trying to find a circuit with a 555 timer that can both independently control the frequency and duty cycle(1% to 99%).

I refer you to the "IC Timer Cookbook", copyright 1977 Walter G. Jung,
Howard W. Sam's Publishing, cat# 21416, ISBN 0-672-21416-4 - Section
5.9.1, page 128. Another hint - it's done with diodes (resistors
charge/discharge the timing caps through different paths). Hint 3 -
quoting from page 130 "A very interesting version of this circuit
results when the timing resistances, Rta and Rtb, are made the center-
to-end resistances of a single potentiometer. With the arm of the
potentiometer centered, Rta=Rtb, so the duty cycle will be 50%
producing square waves. As the arm is varied to either side of
center, Rta increases as Rtb decreases (or vice-versa), but the total
resistance remains the same. As a result, the duty cycle can be
varied while the frequency remains the same."
 
J

Jamie

Jan 1, 1970
0
mike said:
When you personally applied this part to the task, how did you manage
the reliable 1% and 99% duty factors with low jitter?
And how did you compensate for the delay through the part?

I used to design pulse/function generators for a living, so be
as technical as necessary.

I don't give a shit what you used to do. Just like you don't
give a shit what I do or have done..

Do you really think that since this person has started using the
555's or LM393 that he is really worried about fucking jitter? If that
was the case, he should of shot any one for suggesting to use those, but
since this isn't the case, he obviously does not care about that and
more than likely the equipment he is using wouldn't be able to detect
it.

You come off like you're some damn god or something, I can say that
you are marginal compared to a few I know, they would make you look
like you're just starting Electronics 101 with a fringing radio shack
do it yourself kit.

So, making pulse generators must of been a failed adventure for you, I
can see where that could be a possibility, or was it your attitude of
open mouth and insert foot, which is more likely.

P.S.

I've been here for some time now monitoring when I can and I can
tell you, you aren't anything special. And you'd be a fool to think
otherwise.

And btw, I do know how to reduce jitter down to a minimum to the point
where is almost nonexistent, but I'll leave that up to you, since you
are the one that made PULSE! generates for a living, you must of been
starving.


Jamie
 
M

mike

Jan 1, 1970
0
I don't give a shit what you used to do. Just like you don't
give a shit what I do or have done..

Do you really think that since this person has started using the
555's or LM393 that he is really worried about fucking jitter? If that
was the case, he should of shot any one for suggesting to use those, but
since this isn't the case, he obviously does not care about that and
more than likely the equipment he is using wouldn't be able to detect
it.

You come off like you're some damn god or something, I can say that you
are marginal compared to a few I know, they would make you look
like you're just starting Electronics 101 with a fringing radio shack
do it yourself kit.

So, making pulse generators must of been a failed adventure for you, I
can see where that could be a possibility, or was it your attitude of
open mouth and insert foot, which is more likely.

P.S.

I've been here for some time now monitoring when I can and I can tell
you, you aren't anything special. And you'd be a fool to think otherwise.

And btw, I do know how to reduce jitter down to a minimum to the point
where is almost nonexistent, but I'll leave that up to you, since you
are the one that made PULSE! generates for a living, you must of been
starving.


Jamie
Sorry you're upset. I thought I'd just asked two questions so that
I might learn something that might improve my designs. Just wanted
you to know that you needn't dumb it down for me.

If you'd care to teach me/us about reducing jitter to almost nonexistent,
I'd appreciate having the techniques in my toolbox.
I like to learn new things.
 
J

Jamie

Jan 1, 1970
0
mike said:
Sorry you're upset. I thought I'd just asked two questions so that
I might learn something that might improve my designs. Just wanted
you to know that you needn't dumb it down for me.

If you'd care to teach me/us about reducing jitter to almost nonexistent,
I'd appreciate having the techniques in my toolbox.
I like to learn new things.
I don't care to teach any one anything to be frank..

I answered the question at the same level as the request.. It was
quite understandable at what level the expected reply would have been.

Jamie
 
M

mike

Jan 1, 1970
0
I don't care to teach any one anything to be frank..

I answered the question at the same level as the request.. It was
quite understandable at what level the expected reply would have been.

Jamie
My first job, I had the good fortune to be assigned to one of the
few competent mentors I've ever met.

One of the most important and enduring lessons he taught...by example...
was that it's always more efficient to teach a concept...more than
once...often more than twice, in my case...
than it is to tell someone that they're stupid for not knowing.

When presented with a proposal, FIRST THINK. Then
ask a few pointed questions to probe areas where their understanding
exceeds yours. The worst that can happen is that you learn something.
You can usually tell from the tone of their answer whether they have
anything to
contribute or are even receptive to learning.

Unless they're your boss, you have the option to "opt-out". ;-)

If your first reaction is a rebuttal, you're headed in the wrong
direction.

If your first reaction is personal denigration, you're
in a newsgroup.

YMMV
 
J

Jamie

Jan 1, 1970
0
mike said:
My first job, I had the good fortune to be assigned to one of the
few competent mentors I've ever met.

One of the most important and enduring lessons he taught...by example...
was that it's always more efficient to teach a concept...more than
once...often more than twice, in my case...
than it is to tell someone that they're stupid for not knowing.

When presented with a proposal, FIRST THINK. Then
ask a few pointed questions to probe areas where their understanding
exceeds yours. The worst that can happen is that you learn something.
You can usually tell from the tone of their answer whether they have
anything to
contribute or are even receptive to learning.

Unless they're your boss, you have the option to "opt-out". ;-)

If your first reaction is a rebuttal, you're headed in the wrong
direction.

If your first reaction is personal denigration, you're
in a newsgroup.

YMMV
At age 13 was my first tutored exposure to electronics, I was always
interested in it before that but struggled with reading, as in
understanding the academic world with the reference materials I had.

My first tutor was retired but still did electronic engineering
design and prototype work out of his home. He started as a navy
electronics tech and after he served, he then worked as an engineer at
Lafayette,
Raytheon, RCA and some government work shops, through out his years
before he retired.

He gave me lots and lots of technical manuals and had me help him at
the prototype work and showed me designed engineering in the process.

I got my very first Simpson 260 from him and I still have it, as a
memory keepsake. He also gave me all kinds of tools to work with, scope,
generator etc. All this after a couple of years visiting mostly in the
summer months, because he was just down the road from me and I was
in school of course.

From there, that open the doors for me to get schooled, jobbed and
adult training over the years in electronics and other related fields.

How I remember building tube circuits and I don't think I ever want to
do that gain. Between the thermal burns and HV burns, I've had my share.

If Only I had the youth and ambition of then with the components of
today, I'd be dangerous.

These days, I only design/prototype when asked for something and not
fill up my house with un-finished experiments!

Jamie
 
R

Ralph Barone

Jan 1, 1970
0
Jim Thompson said:
[snip]
My first job, I had the good fortune to be assigned to one of the
few competent mentors I've ever met.

One of the most important and enduring lessons he taught...by example...
was that it's always more efficient to teach a concept...more than
once...often more than twice, in my case...
than it is to tell someone that they're stupid for not knowing.

When presented with a proposal, FIRST THINK. Then
ask a few pointed questions to probe areas where their understanding
exceeds yours. The worst that can happen is that you learn something.
You can usually tell from the tone of their answer whether they have
anything to
contribute or are even receptive to learning.

Speaking of mentoring, this was posted recently to my LinkedIn profile
by a person I can't even remember working with....

[snip]
"I have had the pleasure of working on and off with Jim since 1989 at
Honeywell and also as a contractor. Jim is one of the most creative
inventors and truly one of the early pioneers of many famous circuits.
I learned a great deal from Jim yet only scratched the surface of his
knowledge. Jim is also a real kick to talk to and work with great
people skills. Jim has probably the most experience, noted by his many
accomplishments, of any designer I know. I've known a lot. Jim is a
great asset to have as he will always come up with something elegant,
making you think, “Now why didn't I think of that, it was right under
my nose?” I highly recommend Jim and would gladly work with him in the
future."

...Jim Thompson

Sounds like the type of person I would like to encounter on Usenet.
 
J

Jasen Betts

Jan 1, 1970
0
Hello,

I'm on a quest here.
I am trying to find a circuit with a 555 timer that can both independently control the frequency and duty cycle(1% to 99%).
Most circuit I find is either or, A few was actually what I thought
i needed but when completing the circuit, I found that when varying
the frequency.. the duty cycle was also changing !! or vice versa.


here's how to do it with 2 555s.
You'll need to use a fixed-pitch font to make this legible

+V
|
.---------------------------.
| | |
| .--------+--------------------+--------+------------+
| | | | | | |
| | . . . .|. . . . freq. | | . . . .|. . . . |
| | . VCC(8) . __ | | . VCC(8) . |
| | . . /| | | . . | out
| `--RES(4) OUT(3)---/\/\/--+ +--RES(4) OUT(3)----------
| . 555 . / | | . 555 . |
+----TH(6) DIS(7)-- | +--TH(6) DIS(7)-- \
| . . | . . \ / duty
`----TR(2) CV(5)-- +------TR(2) CV(5)----->\ cycle
. . | . . / /
. GND(1) . === . GND(1) . | 10K
. . . .|. . . . | . . . .|. . . . |
| | | |
----------+----------------+------------+------------+--

neither control will be particularly liner (freq will adjust the
period in an approximately linear fashion) and duty cycle will be
non-linear in two different ways (and have dead zones at each end)
one of the non-linearities can be improved by adding an NPN
emitter follower between the potentiometer and pin 5.
(collector to +v)


if you can use a variable capacitor for frequency you
can use the single 555, two-diodes varialble duty cycle
circuit that's all over the web.
I know with a LM393, (and I have that circuit) it is possible.

LM339 ? there may be a way to speed that up,.
 
C

captoro

Jan 1, 1970
0
Hello,



I'm on a quest here.

I am trying to find a circuit with a 555 timer that can both independently control the frequency and duty cycle(1% to 99%).

Most circuit I find is either or, A few was actually what I thought i needed but when completing the circuit, I found that when varying the frequency.. the duty cycle was also changing !! or vice versa.

I know with a LM393, (and I have that circuit) it is possible. but it is not fast enough. I can see on the scope that the 555 pulse starts to deteriorates 2.5us while the lm393 starts about at 100us

thanks for the help



ken

Actually I have been working on a pic version of this. I get much faster rise time (not clocking) then a Lm393 or a 555 timer. Yes in the nanosecond, But the 555 is in the microseconds. Unless I am mistaken... which happened before :()

Ken
 
C

captoro

Jan 1, 1970
0
Actually I have been working on a pic version of this. I get much faster rise time (not clocking) then a Lm393 or a 555 timer. Yes in the nanosecond, But the 555 is in the microseconds. Unless I am mistaken... which happened before :()



Ken

Just to clear up a few things. I am looking to obtain dutycycle from 1% to 100% and frequency from 200 to 2khz with fast rise and fall time. I saw someone posted the mc10eo195 chip, very fast rise and fall time.... in picoseconds ! I will look into that.

K
 
B

Bill Sloman

Jan 1, 1970
0
Just to clear up a few things. I am looking to obtain dutycycle from 1% to
100% and frequency from 200 to 2khz with fast rise and fall time. I saw
someone posted the mc10eo195 chip, very fast rise and fall time.... in
picoseconds ! I will look into that.

That was in the context of an all-digital solution. If you read that post more carefully, you'd realise that what you need is (for a 2kHz maximum frequency) a 2MHz clock oscillator and a pair of 14-bit counters. The MC100EP195 doesn't make sense if you don't want frequencies above 2MHz. For a 2kHz maximum they'd be ridiculous.

As before, I'd recommend buying the 2MHz oscillator off the shelf, and realising the two 14-bit counters in a programmable logic device. I've got a weakness for the Xilinx CoolRunner parts, and they are quite big enough and fast enough for the job.

You might want to use Binary-Coded Decimal thumb switches to set up the twodividers. That's four pins per decade, and you'd have to think about how finely you;d want to be able to program the frequency and the mark-to-space ratio - you'd need 16-bits (4 4-bit decade counters) to cover your range ifyou wanted 0.5usec resolution on both periods, and 32 input pins to tell the programmable logic part what you wanted.

A PIC might be a bit easier. One with an A/D converter might decode your settings from a pair of potentiometers, which might offer a tidier and more intuitive user interface. Ten-turn pots and turns-counting dials have gottenrare and expensive in recent years, but they are tidier than direct digital inputs.
 
M

Martin Brown

Jan 1, 1970
0
I refer you to the "IC Timer Cookbook", copyright 1977 Walter G. Jung,
Howard W. Sam's Publishing, cat# 21416, ISBN 0-672-21416-4 - Section
5.9.1, page 128. Another hint - it's done with diodes (resistors
charge/discharge the timing caps through different paths). Hint 3 -
quoting from page 130 "A very interesting version of this circuit
results when the timing resistances, Rta and Rtb, are made the center-
to-end resistances of a single potentiometer. With the arm of the
potentiometer centered, Rta=Rtb, so the duty cycle will be 50%
producing square waves. As the arm is varied to either side of
center, Rta increases as Rtb decreases (or vice-versa), but the total
resistance remains the same. As a result, the duty cycle can be
varied while the frequency remains the same."

You have obviously never built this circuit. It "remains the same" only
very roughly. ie - you don't have to be a musician to hear a change in
frequency as the mark space ratio is altered away from 50%.

I have wondered if it was possible to design a more complex network to
get something closer to idealised behaviour. Obviously increasing the
operating voltage and using Schottky diodes helps a bit.

The lazy way I found was a pair of 555s with a regulated supply one to
set frequency and the other as a triggered monostable - the purpose
being for a demonstration on sound waveforms to show how the character
of a sound at constant pitch changed with mark space ratio. I also had
to make the total power remain about constant too for this and provide
envelope modulation (piano or guitar backwards is particularly fun).

It depends a bit on the range of frequencies it has to cover whether or
not this would be an acceptable solution for the OP.
 
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