>> I want to know if is possible use the V.22bis modem
standard
>> for dial-up internet access (Internet Service Provider) ?.
>We produced a TCP/IP stack, optimised for low-memory
systems, and at
>one stage ran it on the V.22bis (2400bps) modem. It was a very neat
>fast training time. I'm not aware of any large scale use of TCP/IP at
>such speeds, though.
>
>In summary: it can be done, but it's unlikely to be that useful in a
>real-world application.
Iridium Satellite can only support 2400bps data connections, and
therefore their internet offerings use this speed (with data compression
to up the effective speed in most instances; claiming 9k6). That's an
example of a pretty widespread real-world application at that sort of
speed.
Cheers,
Bruce
BPSK Demodulation with LPC214X
Started by ●April 27, 2007
Reply by ●April 30, 20072007-04-30
Reply by ●April 30, 20072007-04-30
--- In l..., "Brendan Murphy"
wrote:
>
> --- In l..., "John Heenan" wrote:
> >
> > --- In l..., Tom Walsh wrote:
> > >
> > > My point is that anything / anybody can look good on paper.
> > >
> > > Regards,
> > >
> > > TomW
> >
> > What you say is common in many disciplines. But knowing that most
of
> > those you are interviewing are hopelessly unrealistic, untried,
have
> > no respect for those they see as standing in the way of their
bright
> > ideas fantasies, have dubious honesty and have been clever at
playing
> > the game does not alter that they are the stock you must choose
from
> [[and plenty more of the same....]]
>
> Guys, what possible relevance has any of this to a Group devoted to
the
> NXP LPC2xxx?
>
What good is any device if you cannot get the talent to make it work?
I am a bit surprised and puzzled at your comment Brendan. You stated
are a software guy in the context of analogue issues and gave little
further information. Tom said he demodulates BPSK with adc, you
stated you use microcontrollers to minimise additional analogue
components and stated you had problems filtering out a pwm carrier
which can be avoided by using the dac (which you stated was messy
with the NXP LPC2xxx with regard to triggering).
I have no wish to question your design approach Brendan but you
brought up issues that lead to the question of the availability of
analogue talent in the context of digital devices.
You appear not to regard yourself as an 'analogue guy' Brendan. But
are you able to get good analogue talent when you want it? Have you
tried? Can new graduates in electronic engineering become productive
within existing projects with analogue design quickly?
Filtering techniques are an important part of the arsenal of the
electronics engineer. Getting a board layout right can mean the
difference between passing compliance tests and failing them.
My own experience is that when it comes to analogue talent there are
lots of pretenders but few who can actually deliver. I have had to go
through a painful process of going well beyond the limited amount I
learnt decades ago. I am pleased it is paying off. Doubtless you will
regard this as irrelevant also.
John Heenan
wrote:
>
> --- In l..., "John Heenan" wrote:
> >
> > --- In l..., Tom Walsh wrote:
> > >
> > > My point is that anything / anybody can look good on paper.
> > >
> > > Regards,
> > >
> > > TomW
> >
> > What you say is common in many disciplines. But knowing that most
of
> > those you are interviewing are hopelessly unrealistic, untried,
have
> > no respect for those they see as standing in the way of their
bright
> > ideas fantasies, have dubious honesty and have been clever at
playing
> > the game does not alter that they are the stock you must choose
from
> [[and plenty more of the same....]]
>
> Guys, what possible relevance has any of this to a Group devoted to
the
> NXP LPC2xxx?
>
What good is any device if you cannot get the talent to make it work?
I am a bit surprised and puzzled at your comment Brendan. You stated
are a software guy in the context of analogue issues and gave little
further information. Tom said he demodulates BPSK with adc, you
stated you use microcontrollers to minimise additional analogue
components and stated you had problems filtering out a pwm carrier
which can be avoided by using the dac (which you stated was messy
with the NXP LPC2xxx with regard to triggering).
I have no wish to question your design approach Brendan but you
brought up issues that lead to the question of the availability of
analogue talent in the context of digital devices.
You appear not to regard yourself as an 'analogue guy' Brendan. But
are you able to get good analogue talent when you want it? Have you
tried? Can new graduates in electronic engineering become productive
within existing projects with analogue design quickly?
Filtering techniques are an important part of the arsenal of the
electronics engineer. Getting a board layout right can mean the
difference between passing compliance tests and failing them.
My own experience is that when it comes to analogue talent there are
lots of pretenders but few who can actually deliver. I have had to go
through a painful process of going well beyond the limited amount I
learnt decades ago. I am pleased it is paying off. Doubtless you will
regard this as irrelevant also.
John Heenan
Reply by ●April 30, 20072007-04-30
--- In l..., "John Heenan" wrote:
> What good is any device if you cannot get the talent to make it
work?
>
> I am a bit surprised and puzzled at your comment Brendan. You
stated
> are a software guy in the context of analogue issues and gave
little
> further information. Tom said he demodulates BPSK with adc, you
> stated you use microcontrollers to minimise additional analogue
> components and stated you had problems filtering out a pwm carrier
> which can be avoided by using the dac (which you stated was messy
> with the NXP LPC2xxx with regard to triggering).
>
> I have no wish to question your design approach Brendan but you
> brought up issues that lead to the question of the availability of
> analogue talent in the context of digital devices.
>
> You appear not to regard yourself as an 'analogue guy' Brendan. But
> are you able to get good analogue talent when you want it? Have you
> tried? Can new graduates in electronic engineering become
productive
> within existing projects with analogue design quickly?
>
> Filtering techniques are an important part of the arsenal of the
> electronics engineer. Getting a board layout right can mean the
> difference between passing compliance tests and failing them.
>
> My own experience is that when it comes to analogue talent there
are
> lots of pretenders but few who can actually deliver. I have had to
go
> through a painful process of going well beyond the limited amount I
> learnt decades ago. I am pleased it is paying off. Doubtless you
will
> regard this as irrelevant also.
>
> John Heenan
>
OK - I see where you're coming from now. I think it's based on a
misinterpretation of what I said, though.
Tom asked the following:
I've also been looking at using the ADC for 1200bps demodulation...
How are you doing with noise? I've got to use this via an RF circuit
and you know what they can be like, even FM is somewhat noisy.
/END QUOTE>
My response to the question was that we dealt with the noise in the
digital domain, for the reasons I explained (to minimise hardware). I
also outlined how we did this. This isn't to say it couldn't be dealt
with in hardware through good hardware design. In fact, my comment at
the end was simply meant to acknowledge this: because of our
backgrounds, we were likely to use solutions from our own comfort
zones. Nothing wrong with this: I'm sure Tom would agree.
As it happens, the same product used quite a bit of analog circuit
design expertise (not by me, I hasten to add), precisely to reduce
the hardware requirement. My point here was that we chose to go the
DSP route because it suited, not because we didn't have access to
such expertise.
He then went on to say:
I was thinking about doing modulation via PWM output from a port pin,
then shaping the signal via a series of low pass active filters.
/END QUOTE>
I outlined our own experience of attempting exactly the same
approach. Essentially, what we found was that even with carefully
chosen oversampled rates, you get a lot of noise caused by harmonics
of the PWM "carrier" frequency. Some of these fall in-band, in our
case at sufficiently high levels to cause communication failure. It
was really meant as a warning that the technqiue is noisy (not that
it was needed in Tom's case, I'm sure). I may have been incorrect to
say as I did that the in-band noise couldn't be removed by external
filtering, but in any case we abandoned the approach and used a
regular DAC instead, primaily as we didn't really have the option of
using a lot of hardware to solve the issue.
To finish, I've nothing but the height of respect for anyone with
good analog design skills as you point out it's hard to get these
days. You're quite correct in stating that I don't see myself as an
analog designer (as I said, I'm lucky in having access to someone who
has about 30 years experience in the field, so your assumption about
lack of availability in this case is not correct).
Hopefully, this clarifies matters.
Brendan.
> What good is any device if you cannot get the talent to make it
work?
>
> I am a bit surprised and puzzled at your comment Brendan. You
stated
> are a software guy in the context of analogue issues and gave
little
> further information. Tom said he demodulates BPSK with adc, you
> stated you use microcontrollers to minimise additional analogue
> components and stated you had problems filtering out a pwm carrier
> which can be avoided by using the dac (which you stated was messy
> with the NXP LPC2xxx with regard to triggering).
>
> I have no wish to question your design approach Brendan but you
> brought up issues that lead to the question of the availability of
> analogue talent in the context of digital devices.
>
> You appear not to regard yourself as an 'analogue guy' Brendan. But
> are you able to get good analogue talent when you want it? Have you
> tried? Can new graduates in electronic engineering become
productive
> within existing projects with analogue design quickly?
>
> Filtering techniques are an important part of the arsenal of the
> electronics engineer. Getting a board layout right can mean the
> difference between passing compliance tests and failing them.
>
> My own experience is that when it comes to analogue talent there
are
> lots of pretenders but few who can actually deliver. I have had to
go
> through a painful process of going well beyond the limited amount I
> learnt decades ago. I am pleased it is paying off. Doubtless you
will
> regard this as irrelevant also.
>
> John Heenan
>
OK - I see where you're coming from now. I think it's based on a
misinterpretation of what I said, though.
Tom asked the following:
I've also been looking at using the ADC for 1200bps demodulation...
How are you doing with noise? I've got to use this via an RF circuit
and you know what they can be like, even FM is somewhat noisy.
/END QUOTE>
My response to the question was that we dealt with the noise in the
digital domain, for the reasons I explained (to minimise hardware). I
also outlined how we did this. This isn't to say it couldn't be dealt
with in hardware through good hardware design. In fact, my comment at
the end was simply meant to acknowledge this: because of our
backgrounds, we were likely to use solutions from our own comfort
zones. Nothing wrong with this: I'm sure Tom would agree.
As it happens, the same product used quite a bit of analog circuit
design expertise (not by me, I hasten to add), precisely to reduce
the hardware requirement. My point here was that we chose to go the
DSP route because it suited, not because we didn't have access to
such expertise.
He then went on to say:
I was thinking about doing modulation via PWM output from a port pin,
then shaping the signal via a series of low pass active filters.
/END QUOTE>
I outlined our own experience of attempting exactly the same
approach. Essentially, what we found was that even with carefully
chosen oversampled rates, you get a lot of noise caused by harmonics
of the PWM "carrier" frequency. Some of these fall in-band, in our
case at sufficiently high levels to cause communication failure. It
was really meant as a warning that the technqiue is noisy (not that
it was needed in Tom's case, I'm sure). I may have been incorrect to
say as I did that the in-band noise couldn't be removed by external
filtering, but in any case we abandoned the approach and used a
regular DAC instead, primaily as we didn't really have the option of
using a lot of hardware to solve the issue.
To finish, I've nothing but the height of respect for anyone with
good analog design skills as you point out it's hard to get these
days. You're quite correct in stating that I don't see myself as an
analog designer (as I said, I'm lucky in having access to someone who
has about 30 years experience in the field, so your assumption about
lack of availability in this case is not correct).
Hopefully, this clarifies matters.
Brendan.
Reply by ●April 30, 20072007-04-30
--- In l..., "John Heenan" wrote:
> My own experience is that when it comes to analogue talent there are
> lots of pretenders but few who can actually deliver.
My 2c worth in this digression.
I do not believe your observation is limited to just "analogue
talent". Information technology (e.g. Google) can make it difficult to
distinguish pretenders from performers in many areas, including
software engineering.
One solution is to consider qualifications, experience and other
historical evidence as no more than indicators based on which you
short list candidates. You then examine the candidates by interview
and other interactive methods to determine if the person is really
what his/her historical records suggest.
Jaya
> My own experience is that when it comes to analogue talent there are
> lots of pretenders but few who can actually deliver.
My 2c worth in this digression.
I do not believe your observation is limited to just "analogue
talent". Information technology (e.g. Google) can make it difficult to
distinguish pretenders from performers in many areas, including
software engineering.
One solution is to consider qualifications, experience and other
historical evidence as no more than indicators based on which you
short list candidates. You then examine the candidates by interview
and other interactive methods to determine if the person is really
what his/her historical records suggest.
Jaya
