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bitrex
Guest

Wed Jan 09, 2019 11:45 pm   



On 01/09/2019 09:08 AM, bill.sloman_at_ieee.org wrote:
Quote:
On Wednesday, January 9, 2019 at 3:13:48 PM UTC+11, Robert Martin wrote:
On 9/1/19 11:04 am, bill.sloman_at_ieee.org wrote:
On Wednesday, January 9, 2019 at 10:48:46 AM UTC+11, Robert Martin wrote:
I have a CD4060 outputting a 5Vpp 4Hz (4 hertz) square wave at 50% duty
cycle.

How can I randomly pulse width modulate this so that when a low pass
filter is added a constantly changing, "wave-like" arbitrary waveform
will be produced?

I would prefer analog or CMOS IC's, not a microprocessor, and minimum
parts count.

The "randomness" does not need to be true but only a reasonable
approximation.

Thank you for any ideas or available circuit diagrams.

https://en.wikipedia.org/wiki/Pseudorandom_binary_sequence

You can make a pseudorandnom binary sequence in a single-chip processor - it can also be done with long shift registers, and some parts seem to have been designed for the job, but the single-chip microprocessor or a programmable logic chip are the minimum part solution.


I would prefer not to use a micro.

Of course. You'd have to learn more than the bare minimum required to get the job done.

This circuit uses only two IC's.
http://www.seekic.com/circuit_diagram/Signal_Processing/PSEUDO_RANDOM_BIT_SEQUENCE_GENERATOR.html


Any comments? Would clocking it at 4Hz present any problems?

The circuit uses three integrated circuits - two 5-stage shift register and the exclusive-OR gate package.

It is singularly un-impressive, clearly designed by somebody who couldn't be bother finding out what parts are available.

You can get much longer shift registers - designed for the job - that only provide external output from the stages you need to feed into the exclusive-OR gate, and you can program a programmable-logic device to do all the same jobs in one chip.

Clocking it at 4Hz wouldn't present any problems

Do I understand correctly that the output would be a 4Hz PWM signal at
about 2Vpp?

If you built it with TTL-logic powered from 5V and didn't put a pull-up on the output you'd see about 2V peak to peak.

Most people would use CMOS these days, which would give you rail to rail swing - which could be up to 15V with old 4000-series CMOS. More modern parts are mostly only rated for lower supply voltages - 5V or lower.


I could whip up a code sketch and have an ATTiny 8 pin uP on a board
outputting the required wave form with pseudo-random duty cycle
modulation in literally ten minutes

Robert Martin
Guest

Wed Jan 09, 2019 11:45 pm   



On 10/1/19 1:08 am, bill.sloman_at_ieee.org wrote:

Quote:
This circuit uses only two IC's.
http://www.seekic.com/circuit_diagram/Signal_Processing/PSEUDO_RANDOM_BIT_SEQUENCE_GENERATOR.html


Any comments? Would clocking it at 4Hz present any problems?

The circuit uses three integrated circuits - two 5-stage shift register and the exclusive-OR gate package.

It is singularly un-impressive, clearly designed by somebody who couldn't be bother finding out what parts are available.

You can get much longer shift registers - designed for the job - that only provide external output from the stages you need to feed into the exclusive-OR gate, and you can program a programmable-logic device to do all the same jobs in one chip.

Clocking it at 4Hz wouldn't present any problems

Do I understand correctly that the output would be a 4Hz PWM signal at
about 2Vpp?

If you built it with TTL-logic powered from 5V and didn't put a pull-up on the output you'd see about 2V peak to peak.

Most people would use CMOS these days, which would give you rail to rail swing - which could be up to 15V with old 4000-series CMOS. More modern parts are mostly only rated for lower supply voltages - 5V or lower.


Thank you. I always liked the CMOS logic series. Here is my first
attempt with a CD4021.

https://app.box.com/s/vywrm8iswo3yts3jnyyj19maamla4amq

It is an 8 bit adaptation of this 10 bit circuit I posted earlier.

http://www.seekic.com/circuit_diagram/Signal_Processing/PSEUDO_RANDOM_BIT_SEQUENCE_GENERATOR.html

I am sure there are mistakes, so comments would be very much appreciated.

Robert Martin


Guest

Thu Jan 10, 2019 1:45 am   



On Thursday, January 10, 2019 at 9:18:12 AM UTC+11, Robert Martin wrote:
Quote:
On 10/1/19 1:08 am, bill.sloman_at_ieee.org wrote:

This circuit uses only two IC's.
http://www.seekic.com/circuit_diagram/Signal_Processing/PSEUDO_RANDOM_BIT_SEQUENCE_GENERATOR.html


Any comments? Would clocking it at 4Hz present any problems?

The circuit uses three integrated circuits - two 5-stage shift register and the exclusive-OR gate package.

It is singularly un-impressive, clearly designed by somebody who couldn't be bother finding out what parts are available.

You can get much longer shift registers - designed for the job - that only provide external output from the stages you need to feed into the exclusive-OR gate, and you can program a programmable-logic device to do all the same jobs in one chip.

Clocking it at 4Hz wouldn't present any problems

Do I understand correctly that the output would be a 4Hz PWM signal at
about 2Vpp?

If you built it with TTL-logic powered from 5V and didn't put a pull-up on the output you'd see about 2V peak to peak.

Most people would use CMOS these days, which would give you rail to rail swing - which could be up to 15V with old 4000-series CMOS. More modern parts are mostly only rated for lower supply voltages - 5V or lower.


Thank you. I always liked the CMOS logic series. Here is my first
attempt with a CD4021.

https://app.box.com/s/vywrm8iswo3yts3jnyyj19maamla4amq

It is an 8 bit adaptation of this 10 bit circuit I posted earlier.

http://www.seekic.com/circuit_diagram/Signal_Processing/PSEUDO_RANDOM_BIT_SEQUENCE_GENERATOR.html

I am sure there are mistakes, so comments would be very much appreciated.


I haven't looked at it in detail, but one failure mode with pseudo-random binary sequence generators is that if the shift register gets completely filled with either ones or zeros (depending on the implementation) they don't do anything. A crude - but often effective - solution is to trigger a pair of monstables - one for rising edges and one for falling edged - each time they see a transition, and if neither has been triggered for a period longer than the length of the shift register multiplied by the clock period you set or clear the shift register.

It's short - 8-stages is 256 possible state - so it would repeat once a minute if clocked at 4Hz.

It's decades since I've done it (to confuse bats that a female friend was testing) so this may not be reliable advice.

--
Bill Sloman, Sydney

Robert Martin
Guest

Thu Jan 10, 2019 3:45 am   



On 10/1/19 7:53 am, George Herold wrote:
Quote:
On Wednesday, January 9, 2019 at 3:39:10 PM UTC-5, Robert Martin wrote:
On 10/1/19 12:47 am, George Herold wrote:
On Wednesday, January 9, 2019 at 8:16:36 AM UTC-5, Robert Martin wrote:
On 9/1/19 5:26 pm, bitrex wrote:
On 01/08/2019 06:48 PM, Robert Martin wrote:
I have a CD4060 outputting a 5Vpp 4Hz (4 hertz) square wave at 50%
duty cycle.

How can I randomly pulse width modulate this so that when a low pass
filter is added a constantly changing, "wave-like" arbitrary waveform
will be produced?

I would prefer analog or CMOS IC's, not a microprocessor, and minimum
parts count.

The "randomness" does not need to be true but only a reasonable
approximation.

Thank you for any ideas or available circuit diagrams.

Robert Martin

I think the simplest way to do it without a uP would to build an analog
white noise source a la:

http://www.electro-music.com/forum/phpbb-files/2tran_wn_203.gif

and then aggressively low-pass filter it. then feed your square wave
into one input of a comparator and the appropriately-scaled low-passed
noise into the other.


I tried using noise, as recommended earlier on this group and elsewhere.
The filtered amplitude below 10Hz was too low to produce a workable result,


That makes sense (loss of signal) how about filter it at ~10-100 kHz
and then send it into a counter/ divider to get to lower frequency.

George H.

Good suggestion. I'll first apply a 1KHz LPF and clip its output to
simulate a logic signal into a divide by 100 counter.

Robert Martin

Robert, now that I think about it, I'm not sure that is going to work... or be that useful. If you've got random pulses coming at some rate...
then counting to some number is giving you a running average of the counts
And I don't think you'll see a lot of variation.
One of the pseudo-random shift register things may be better...
you can clock at the rate you like. There are not many low frequency
noise sources... maybe 1/f noise in the old carbon comp resistors?
Geiger counter with weakish source, some chaotic pendulum...

George H.


Thank you for the update.

You are certainly right about a shortage of LF noise sources. A friend
once used a photocell pointed at trees blowing in the wind. Clever but
not very portable.

Robert Martin

Robert Martin
Guest

Thu Jan 10, 2019 3:45 am   



On 10/1/19 9:33 am, bitrex wrote:
Quote:
On 01/09/2019 05:24 PM, bitrex wrote:

Any comments? Would clocking it at 4Hz present any problems?

The circuit uses three integrated circuits - two 5-stage shift
register and the exclusive-OR gate package.

It is singularly un-impressive, clearly designed by somebody who
couldn't be bother finding out what parts are available.

You can get much longer shift registers - designed for the job - that
only provide external output from the stages you need to feed into
the exclusive-OR gate, and you can program a programmable-logic
device to do all the same jobs in  one chip.

Clocking it at 4Hz wouldn't present any problems

Do I understand correctly that the output would be a 4Hz PWM signal at
about 2Vpp?

If you built it with TTL-logic powered from 5V and didn't put a
pull-up on the output you'd see about 2V peak to peak.

Most people would use CMOS these days, which would give you rail to
rail swing - which could be up to 15V with old 4000-series CMOS. More
modern parts are mostly  only rated for lower supply voltages - 5V or
lower.


I could whip up a code sketch and have an ATTiny 8 pin uP on a board
outputting the required wave form with pseudo-random duty cycle
modulation in literally ten minutes

If Robert Martin needs this function in small quantity I could easily do
a thousand of them in a DIP package with the programmer array I have at
home, let's make a deal bro Smile


Thank you for the tempting offer, but I am determined to nut this out
using common IC's, not a micro.

If anyone here is able to design such a circuit that provides a random
PWM output at around 4Hz with low parts count, do let me know. Here
please, not by PM. We can work something out.

Robert Martin

Jasen Betts
Guest

Thu Jan 10, 2019 5:45 am   



On 2019-01-09, Robert Martin <rmartin_at_bristol.edu> wrote:
Quote:

I tried using noise, as recommended earlier on this group and elsewhere.
The filtered amplitude below 10Hz was too low to produce a workable result,

Your idea about using a candlelight flickering LED is interesting, but
looking at the video the switching appears to be a bit sharp.


if you connect a loudspeaker in series with the led it plays "jingle
bells" (or some other music) it's not random.

Quote:
In any case, I would prefer a circuit over which I have a degree of
design control as I may need to tinker to get the chaotic wave-like
effect with smooth transitions that I am looking for.


Maybe Chua's circuit, perhaps folloed by an envelop detector?

--
When I tried casting out nines I made a hash of it.

Jasen Betts
Guest

Thu Jan 10, 2019 5:45 am   



On 2019-01-10, Robert Martin <rmartin_at_bristol.edu> wrote:

Quote:
You are certainly right about a shortage of LF noise sources. A friend
once used a photocell pointed at trees blowing in the wind. Clever but
not very portable.


also somwwhat temporary.

photocell and lava lamp, portable, but heavy, somewhat fragile
and slow to start.

--
When I tried casting out nines I made a hash of it.

Sjouke Burry
Guest

Thu Jan 10, 2019 6:45 am   



On 10-1-2019 5:25, Jasen Betts wrote:
Quote:
On 2019-01-10, Robert Martin <rmartin_at_bristol.edu> wrote:

You are certainly right about a shortage of LF noise sources. A friend
once used a photocell pointed at trees blowing in the wind. Clever but
not very portable.

also somwwhat temporary.

photocell and lava lamp, portable, but heavy, somewhat fragile
and slow to start.

When I needed about 8 low frequency noise signals, I used a noisy zener
diode,
amplified its noise with a video opamp to about 4volts/15MHZ.
Put heavy shielding around that, to avoid radio interference.

I then used 16 sample/hold amplifiers, and let them sample the 15mhz signal,
each shifted a handful of microseconds.
That gave me 6 outputs, each nicely uncorrelated, Filter/amplify to
clean up the
outputs.

You can change the bandwidth by changing the clock for the 16 bit shift
register
controlling the s/h amps.

Used to produce wind and engine noise in a car simulator.

I still have the backplane of sounds generator.

Robert Martin
Guest

Thu Jan 10, 2019 7:45 am   



On 10/1/19 3:21 pm, Jasen Betts wrote:
Quote:
On 2019-01-09, Robert Martin <rmartin_at_bristol.edu> wrote:

I tried using noise, as recommended earlier on this group and elsewhere.
The filtered amplitude below 10Hz was too low to produce a workable result,

Your idea about using a candlelight flickering LED is interesting, but
looking at the video the switching appears to be a bit sharp.

if you connect a loudspeaker in series with the led it plays "jingle
bells" (or some other music) it's not random.


So, it's an audio memory module. Interesting. There are ones based on
the WTV020SD that accpt an SD card. A few dollars each out of China. But
again, not what I was looking for.

Quote:
In any case, I would prefer a circuit over which I have a degree of
design control as I may need to tinker to get the chaotic wave-like
effect with smooth transitions that I am looking for.

Maybe Chua's circuit, perhaps followed by an envelop detector?


http://www.chuacircuits.com/howtobuild2.php

Nice but a bit kinky.

Robert Martins

Peter Heitzer
Guest

Thu Jan 10, 2019 9:45 am   



Robert Martin <rmartin_at_bristol.edu> wrote:
Quote:
I have a CD4060 outputting a 5Vpp 4Hz (4 hertz) square wave at 50% duty
cycle.

How can I randomly pulse width modulate this so that when a low pass
filter is added a constantly changing, "wave-like" arbitrary waveform
will be produced?

I would prefer analog or CMOS IC's, not a microprocessor, and minimum
parts count.

The "randomness" does not need to be true but only a reasonable
approximation.

Thank you for any ideas or available circuit diagrams.

Perhaps you could use a electronic tea light.
If you prefer to build it using standard chips then consider using a noice generator
with a BJT.

--
Dipl.-Inform(FH) Peter Heitzer, peter.heitzer_at_rz.uni-regensburg.de

Phil Hobbs
Guest

Thu Jan 10, 2019 3:45 pm   



On 1/9/19 3:53 PM, George Herold wrote:
Quote:
On Wednesday, January 9, 2019 at 3:39:10 PM UTC-5, Robert Martin wrote:
On 10/1/19 12:47 am, George Herold wrote:
On Wednesday, January 9, 2019 at 8:16:36 AM UTC-5, Robert Martin wrote:
On 9/1/19 5:26 pm, bitrex wrote:
On 01/08/2019 06:48 PM, Robert Martin wrote:
I have a CD4060 outputting a 5Vpp 4Hz (4 hertz) square wave at 50%
duty cycle.

How can I randomly pulse width modulate this so that when a low pass
filter is added a constantly changing, "wave-like" arbitrary waveform
will be produced?

I would prefer analog or CMOS IC's, not a microprocessor, and minimum
parts count.

The "randomness" does not need to be true but only a reasonable
approximation.

Thank you for any ideas or available circuit diagrams.

Robert Martin

I think the simplest way to do it without a uP would to build an analog
white noise source a la:

http://www.electro-music.com/forum/phpbb-files/2tran_wn_203.gif

and then aggressively low-pass filter it. then feed your square wave
into one input of a comparator and the appropriately-scaled low-passed
noise into the other.


I tried using noise, as recommended earlier on this group and elsewhere.
The filtered amplitude below 10Hz was too low to produce a workable result,


That makes sense (loss of signal) how about filter it at ~10-100 kHz
and then send it into a counter/ divider to get to lower frequency.

George H.

Good suggestion. I'll first apply a 1KHz LPF and clip its output to
simulate a logic signal into a divide by 100 counter.

Robert Martin

Robert, now that I think about it, I'm not sure that is going to work... or be that useful. If you've got random pulses coming at some rate...
then counting to some number is giving you a running average of the counts
And I don't think you'll see a lot of variation.
One of the pseudo-random shift register things may be better...
you can clock at the rate you like. There are not many low frequency
noise sources... maybe 1/f noise in the old carbon comp resistors?
Geiger counter with weakish source, some chaotic pendulum...

George H.


Yup, the central limit theorem will make the duty cycle approach 50% as
the division ratio goes up. That's actually pretty useful sometimes,
e.g. in building noise servos based on false-count rates.

A PRBS generator's output is periodic, and so consists entirely of
harmonics of f_clk/(2**N -1), where N is the register length. Filtering
just changes the harmonic amplitudes.

To make that look continuous, so as to get good noise down below 1 Hz,
you need a fair few bits and a lowish clock frequency, so that the
period is much longer than your measurement.

The OP seems to be making very heavy weather of a simple job. "Too
small to produce a workable result" is a typical example.

An ordinary op amp running with a closed loop gain of 100 dB will
produce a lot of low frequency noise, and give some lowpass filtering as
a bonus. (The amp would need at least 120 dB of open-loop gain, but
there are lots of those around.)

Assuming its 0.1-10 Hz p-p noise is 5 uV, the amplitude would be around
500 mV, not counting resistor noise.

If he uses a chopamp, the noise would even be reasonably close to white,
but it would probably need two stages to get enough gain. An OPA378 has
very flat noise of about 20 nV/sqrt(Hz), so in a 10-Hz bandwidth with a
gain of 100000, that would be about 6 mV. A second stage could make
that anything he likes.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

George Herold
Guest

Thu Jan 10, 2019 5:45 pm   



On Thursday, January 10, 2019 at 9:30:34 AM UTC-5, Phil Hobbs wrote:
Quote:
On 1/9/19 3:53 PM, George Herold wrote:
On Wednesday, January 9, 2019 at 3:39:10 PM UTC-5, Robert Martin wrote:
On 10/1/19 12:47 am, George Herold wrote:
On Wednesday, January 9, 2019 at 8:16:36 AM UTC-5, Robert Martin wrote:
On 9/1/19 5:26 pm, bitrex wrote:
On 01/08/2019 06:48 PM, Robert Martin wrote:
I have a CD4060 outputting a 5Vpp 4Hz (4 hertz) square wave at 50%
duty cycle.

How can I randomly pulse width modulate this so that when a low pass
filter is added a constantly changing, "wave-like" arbitrary waveform
will be produced?

I would prefer analog or CMOS IC's, not a microprocessor, and minimum
parts count.

The "randomness" does not need to be true but only a reasonable
approximation.

Thank you for any ideas or available circuit diagrams.

Robert Martin

I think the simplest way to do it without a uP would to build an analog
white noise source a la:

http://www.electro-music.com/forum/phpbb-files/2tran_wn_203.gif

and then aggressively low-pass filter it. then feed your square wave
into one input of a comparator and the appropriately-scaled low-passed
noise into the other.


I tried using noise, as recommended earlier on this group and elsewhere.
The filtered amplitude below 10Hz was too low to produce a workable result,


That makes sense (loss of signal) how about filter it at ~10-100 kHz
and then send it into a counter/ divider to get to lower frequency.

George H.

Good suggestion. I'll first apply a 1KHz LPF and clip its output to
simulate a logic signal into a divide by 100 counter.

Robert Martin

Robert, now that I think about it, I'm not sure that is going to work... or be that useful. If you've got random pulses coming at some rate...
then counting to some number is giving you a running average of the counts
And I don't think you'll see a lot of variation.
One of the pseudo-random shift register things may be better...
you can clock at the rate you like. There are not many low frequency
noise sources... maybe 1/f noise in the old carbon comp resistors?
Geiger counter with weakish source, some chaotic pendulum...

George H.


Yup, the central limit theorem will make the duty cycle approach 50% as
the division ratio goes up. That's actually pretty useful sometimes,
e.g. in building noise servos based on false-count rates.

A PRBS generator's output is periodic, and so consists entirely of
harmonics of f_clk/(2**N -1), where N is the register length. Filtering
just changes the harmonic amplitudes.

To make that look continuous, so as to get good noise down below 1 Hz,
you need a fair few bits and a lowish clock frequency, so that the
period is much longer than your measurement.

The OP seems to be making very heavy weather of a simple job. "Too
small to produce a workable result" is a typical example.

An ordinary op amp running with a closed loop gain of 100 dB will
produce a lot of low frequency noise, and give some lowpass filtering as
a bonus. (The amp would need at least 120 dB of open-loop gain, but
there are lots of those around.)

Assuming its 0.1-10 Hz p-p noise is 5 uV, the amplitude would be around
500 mV, not counting resistor noise.

Yeah that might work (gain up the 1/f noise of an opamp.)
or use my favorite noise source a 20V zener run at ~10 uA of current.

George H.
Quote:
If he uses a chopamp, the noise would even be reasonably close to white,
but it would probably need two stages to get enough gain. An OPA378 has
very flat noise of about 20 nV/sqrt(Hz), so in a 10-Hz bandwidth with a
gain of 100000, that would be about 6 mV. A second stage could make
that anything he likes.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com



Guest

Thu Jan 10, 2019 8:45 pm   



On Thursday, January 10, 2019 at 9:30:34 AM UTC-5, Phil Hobbs wrote:
Quote:
On 1/9/19 3:53 PM, George Herold wrote:
On Wednesday, January 9, 2019 at 3:39:10 PM UTC-5, Robert Martin wrote:
On 10/1/19 12:47 am, George Herold wrote:
On Wednesday, January 9, 2019 at 8:16:36 AM UTC-5, Robert Martin wrote:
On 9/1/19 5:26 pm, bitrex wrote:
On 01/08/2019 06:48 PM, Robert Martin wrote:
I have a CD4060 outputting a 5Vpp 4Hz (4 hertz) square wave at 50%
duty cycle.

How can I randomly pulse width modulate this so that when a low pass
filter is added a constantly changing, "wave-like" arbitrary waveform
will be produced?

I would prefer analog or CMOS IC's, not a microprocessor, and minimum
parts count.

The "randomness" does not need to be true but only a reasonable
approximation.

Thank you for any ideas or available circuit diagrams.

Robert Martin

I think the simplest way to do it without a uP would to build an analog
white noise source a la:

http://www.electro-music.com/forum/phpbb-files/2tran_wn_203.gif

and then aggressively low-pass filter it. then feed your square wave
into one input of a comparator and the appropriately-scaled low-passed
noise into the other.


I tried using noise, as recommended earlier on this group and elsewhere.
The filtered amplitude below 10Hz was too low to produce a workable result,


That makes sense (loss of signal) how about filter it at ~10-100 kHz
and then send it into a counter/ divider to get to lower frequency.

George H.

Good suggestion. I'll first apply a 1KHz LPF and clip its output to
simulate a logic signal into a divide by 100 counter.

Robert Martin

Robert, now that I think about it, I'm not sure that is going to work... or be that useful. If you've got random pulses coming at some rate...
then counting to some number is giving you a running average of the counts
And I don't think you'll see a lot of variation.
One of the pseudo-random shift register things may be better...
you can clock at the rate you like. There are not many low frequency
noise sources... maybe 1/f noise in the old carbon comp resistors?
Geiger counter with weakish source, some chaotic pendulum...

George H.


Yup, the central limit theorem will make the duty cycle approach 50% as
the division ratio goes up. That's actually pretty useful sometimes,
e.g. in building noise servos based on false-count rates.

A PRBS generator's output is periodic, and so consists entirely of
harmonics of f_clk/(2**N -1), where N is the register length. Filtering
just changes the harmonic amplitudes.

To make that look continuous, so as to get good noise down below 1 Hz,
you need a fair few bits and a lowish clock frequency, so that the
period is much longer than your measurement.

The OP seems to be making very heavy weather of a simple job. "Too
small to produce a workable result" is a typical example.

An ordinary op amp running with a closed loop gain of 100 dB will
produce a lot of low frequency noise, and give some lowpass filtering as
a bonus. (The amp would need at least 120 dB of open-loop gain, but
there are lots of those around.)

Assuming its 0.1-10 Hz p-p noise is 5 uV, the amplitude would be around
500 mV, not counting resistor noise.

If he uses a chopamp, the noise would even be reasonably close to white,
but it would probably need two stages to get enough gain. An OPA378 has
very flat noise of about 20 nV/sqrt(Hz), so in a 10-Hz bandwidth with a
gain of 100000, that would be about 6 mV. A second stage could make
that anything he likes.


All you'll end up making with that setup is a thermal gradient/ microphonics detector that outputs a bunch of off scale DC level jumps that take minutes to settle back down.


Quote:

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com


Phil Hobbs
Guest

Thu Jan 10, 2019 11:45 pm   



On 1/10/19 2:18 PM, bloggs.fredbloggs.fred_at_gmail.com wrote:
Quote:
On Thursday, January 10, 2019 at 9:30:34 AM UTC-5, Phil Hobbs wrote:
On 1/9/19 3:53 PM, George Herold wrote:
On Wednesday, January 9, 2019 at 3:39:10 PM UTC-5, Robert Martin wrote:
On 10/1/19 12:47 am, George Herold wrote:
On Wednesday, January 9, 2019 at 8:16:36 AM UTC-5, Robert Martin wrote:
On 9/1/19 5:26 pm, bitrex wrote:
On 01/08/2019 06:48 PM, Robert Martin wrote:
I have a CD4060 outputting a 5Vpp 4Hz (4 hertz) square wave at 50%
duty cycle.

How can I randomly pulse width modulate this so that when a low pass
filter is added a constantly changing, "wave-like" arbitrary waveform
will be produced?

I would prefer analog or CMOS IC's, not a microprocessor, and minimum
parts count.

The "randomness" does not need to be true but only a reasonable
approximation.

Thank you for any ideas or available circuit diagrams.

Robert Martin

I think the simplest way to do it without a uP would to build an analog
white noise source a la:

http://www.electro-music.com/forum/phpbb-files/2tran_wn_203.gif

and then aggressively low-pass filter it. then feed your square wave
into one input of a comparator and the appropriately-scaled low-passed
noise into the other.


I tried using noise, as recommended earlier on this group and elsewhere.
The filtered amplitude below 10Hz was too low to produce a workable result,


That makes sense (loss of signal) how about filter it at ~10-100 kHz
and then send it into a counter/ divider to get to lower frequency.

George H.

Good suggestion. I'll first apply a 1KHz LPF and clip its output to
simulate a logic signal into a divide by 100 counter.

Robert Martin

Robert, now that I think about it, I'm not sure that is going to work... or be that useful. If you've got random pulses coming at some rate...
then counting to some number is giving you a running average of the counts
And I don't think you'll see a lot of variation.
One of the pseudo-random shift register things may be better...
you can clock at the rate you like. There are not many low frequency
noise sources... maybe 1/f noise in the old carbon comp resistors?
Geiger counter with weakish source, some chaotic pendulum...

George H.


Yup, the central limit theorem will make the duty cycle approach 50% as
the division ratio goes up. That's actually pretty useful sometimes,
e.g. in building noise servos based on false-count rates.

A PRBS generator's output is periodic, and so consists entirely of
harmonics of f_clk/(2**N -1), where N is the register length. Filtering
just changes the harmonic amplitudes.

To make that look continuous, so as to get good noise down below 1 Hz,
you need a fair few bits and a lowish clock frequency, so that the
period is much longer than your measurement.

The OP seems to be making very heavy weather of a simple job. "Too
small to produce a workable result" is a typical example.

An ordinary op amp running with a closed loop gain of 100 dB will
produce a lot of low frequency noise, and give some lowpass filtering as
a bonus. (The amp would need at least 120 dB of open-loop gain, but
there are lots of those around.)

Assuming its 0.1-10 Hz p-p noise is 5 uV, the amplitude would be around
500 mV, not counting resistor noise.

If he uses a chopamp, the noise would even be reasonably close to white,
but it would probably need two stages to get enough gain. An OPA378 has
very flat noise of about 20 nV/sqrt(Hz), so in a 10-Hz bandwidth with a
gain of 100000, that would be about 6 mV. A second stage could make
that anything he likes.

All you'll end up making with that setup is a thermal gradient/ microphonics detector that outputs a bunch of off scale DC level jumps that take minutes to settle back down.


If your layout is sufficiently horrible and you pick the wrong parts. A
chopamp and a couple of SMT resistors isn't going to give any problems
in a sane layout.

I gather you're speaking from experience? ;)

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

Robert Martin
Guest

Fri Jan 11, 2019 5:45 am   



On 11/1/19 9:44 am, Phil Hobbs wrote:

Quote:
The OP seems to be making very heavy weather of a simple job.  "Too
small to produce a workable result" is a typical example.

An ordinary op amp running with a closed loop gain of 100 dB will
produce a lot of low frequency noise, and give some lowpass filtering as
a bonus.  (The amp would need at least 120 dB of open-loop gain, but
there are lots of those around.)

Assuming its 0.1-10 Hz p-p noise is 5 uV, the amplitude would be around
500 mV, not counting resistor noise.

If he uses a chopamp, the noise would even be reasonably close to white,
but it would probably need two stages to get enough gain.  An OPA378 has
very flat noise of about 20 nV/sqrt(Hz), so in a 10-Hz bandwidth with a
gain of 100000, that would be about 6 mV.  A second stage could make
that anything he likes.

All you'll end up making with that setup is a thermal gradient/
microphonics detector that outputs a bunch of off scale DC level jumps
that take minutes to settle back down.

If your layout is sufficiently horrible and you pick the wrong parts.  A
chopamp and a couple of SMT resistors isn't going to give any problems
in a sane layout.


How about if I use junction white noise, add a 1KHz LPF and bias the
input of an op amp so it only sees the highest amplitude spikes.

I have no idea what the rep rate of those spikes might be, but I may be
able to adjust so it is primarily within the sub audio range.

These could used as is, or to trigger a square wave which in turn could
be filtered to approximate a sine.

Robert Martin

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