voltage to freq converter

[PDRUNEN]

Hi All,

I want to take an analog voltage, 0-5 volts and convert over to a PWM signal
with fixed period. The on time of the PWM would be based on the input voltage.

This PWM signal will travel over a opto device for isolation and then be
converted back to a analog voltage.

I have been reviewing the net and see Analog Devices has a really good handle
on this type of thing, but they are out of the budget for my application.

Any one have a good "cost effective" solution to such a requirement?

 

[Rene Tschaggelar]

PDRUNEN wrote:

Hi All,

I want to take an analog voltage, 0-5 volts and convert over to a PWM signal
with fixed period. The on time of the PWM would be based on the input voltage.

This PWM signal will travel over a opto device for isolation and then be
converted back to a analog voltage.

I have been reviewing the net and see Analog Devices has a really good handle
on this type of thing, but they are out of the budget for my application.

Any one have a good "cost effective" solution to such a requirement?

Apparently you are not seeking a voltage to frequency converter,
but just a PWM. This can be achieved with a constant current source
loading a cap and a fet unloading the cap at fixed intervalls.
Some do that with a 555. Then a comparator, such as a LM339.

Rene
--
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net

 

[martin griffith]

On Fri, 08 Oct 2004 13:31:20 +0200, in sci.electronics.design you
wrote:

PDRUNEN wrote:
Hi All,

I want to take an analog voltage, 0-5 volts and convert over to a PWM signal
with fixed period. The on time of the PWM would be based on the input voltage.

This PWM signal will travel over a opto device for isolation and then be
converted back to a analog voltage.

I have been reviewing the net and see Analog Devices has a really good handle
on this type of thing, but they are out of the budget for my application.

Any one have a good "cost effective" solution to such a requirement?

Apparently you are not seeking a voltage to frequency converter,
but just a PWM. This can be achieved with a constant current source
loading a cap and a fet unloading the cap at fixed intervalls.
Some do that with a 555. Then a comparator, such as a LM339.

Rene
something like this?

http://www.solorb.com/elect/solarcirc/pwm2/index.html



martin

Serious error.
All shortcuts have disappeared.
Screen. Mind. Both are blank.

 

[Christian Rausch]

PDRUNEN,

an old classic is the 3524 (SG3524, LM3524, UC3524, ...) and this is
probably what you want. As far as I know, it sells for less than 50 (euro or
US) cents.
Have a look at National's application note AN292 for application examples.

Christian


"PDRUNEN" <pdrunen@aol.com> schrieb im Newsbeitrag
news:20041008054627.16217.00000411@mb-m01.aol.com...

Hi All,

I want to take an analog voltage, 0-5 volts and convert over to a PWM
signal
with fixed period. The on time of the PWM would be based on the input
voltage.

This PWM signal will travel over a opto device for isolation and then be
converted back to a analog voltage.

I have been reviewing the net and see Analog Devices has a really good
handle
on this type of thing, but they are out of the budget for my application.

Any one have a good "cost effective" solution to such a requirement?

 

[Joerg]

Hi PDRUNEN,

The LM331 from National is a nice V/F converter chip.

Regards, Joerg

http://www.analogconsultants.com

 

[Nicholas O. Lindan]

"Nicholas O. Lindan" <see@sig.com> wrote

AD654 V/F ... Seventy five cents?

Hoo boy, blew that price. Closer to $4.00 in quantity.

http://www.analog.com/en/prod/0%2C2877%2CAD654%2C00.html

Repeat 1,000 times "Check first, post second ..."
--
Nicholas O. Lindan, Cleveland, Ohio
Consulting Engineer: Electronics; Informatics; Photonics.
Remove spaces etc. to reply: n o lindan at net com dot com
psst.. want to buy an f-stop timer? nolindan.com/da/fstop/

 

[Joerg]

Hi Nicholas,

Seventy five cents? With a bit of a song-and-dance AD will send a sample for
free.


The only way to make it happen at that cost and with fixed frequency

would be an oscillator and a current ramp into a cap that starts fresh
every rising clock edge. Then a comparator would switch when Vin equals
Vramp and, bingo. Kind of a poor man's slope conversion.

Or run it into a uC per dual slope conversion and send in any code, PWM,
whatever. But I guess that would have to be one of those Chinese 4Bit
chips then.

What's the application, a Mattel toy (where major projects
are initiated to shave off $0.03)?

$0.03 x 1,000,000 = $30,000.00


It's not only Mattel. Same for diposable med stuff. We sometimes

calculate in "Milli-Dollars".

Regards, Joerg

http://www.analogconsultants.com

 

[Joerg]

Hi Nicholas,

That may be the cheapest way: There's lots of 75c micros out there with
at least a comparator input - add an R and a C and a bit of software and
away you go.


Plus a crystal. But in this case it can be almost any frequency. I like

the MSP chips that only need a 32KHz watch crystal because those
crystals are between a dime and a nickel. The higher frequency is made
internally via a frequency control loop, something like a poor man's
PLL. Pretty smart, works nicely.

But I guess that would have to be one of those Chinese 4Bit
chips then.



Oh, horrors.


Where the documentation is not necessarily available in English, of

course....

Gee, and here most folks thought that 'med stuff' was calculated in
Milli(on)-Dollars.


Not anymore, at least not since everyone has to fight for that coveted

Medicare 'reimbursement number', HMO endorsements and so on. When it
comes to disposables like your squirt gun every penny counts nowadays.
50 Cents would be a huge amount of money in that field.

There was an ad in EDN et. al. with the picture of a car's C-Pillar and
the line: "The boss ordered you to take 75c out of the design to pay for
the opera windows". It was the 70's. The tasteless era: pale green
leisure suits, 100% polyester drip-dry shirts, white belt and shoes:
wearing all that at one time was called 'A full Cleveland'.


I lived in Europe back then but it was similar. Ugly sideburns, clashing

colors, disgusting pop music. I mean, I really liked the Stones but much
of the other stuff, yuck. Also, I doggedly stuck to cotton shirts,
mostly the lumberjack style, listened to country music and Wolfman Jack,
and avoided "modern" plastic stuff like the plague. It's still the same
except that Wolfman Jack ain't around anymore.

Regards, Joerg

http://www.analogconsultants.com

 

[Ken Smith]

In article <u_S9d.8768$nj.5832@newssvr13.news.prodigy.com>,
Joerg <notthisjoergsch@removethispacbell.net> wrote:

Hi Nicholas,

That may be the cheapest way: There's lots of 75c micros out there with
at least a comparator input - add an R and a C and a bit of software and
away you go.


Plus a crystal. But in this case it can be almost any frequency. I like

Many of the micros on the market today can get by without a crystal unless
you want a very accurate frequency.


--
--
kensmith@rahul.net forging knowledge

 

[Nicholas O. Lindan]

"Joerg" <notthisjoergsch@removethispacbell.net> wrote

Nicholas Lindan wrote:
That may be the cheapest way: There's lots of 75c micros

Plus a crystal.
Or an R and a C. If it is PWM instead of V/F then all the timing is

relative.

There was an ad in EDN et. al. with the picture of a car's C-Pillar and
the line: "The boss ordered you to take 75c out of the design to pay for
the opera windows". It was the 70's. The tasteless era: pale green
leisure suits, 100% polyester drip-dry shirts, white belt and shoes:
wearing all that together was called 'A full Cleveland'.

I lived in Europe back then but it was similar. Ugly sideburns, clashing
colors,

Dark brown and burnt orange plastic for restaurant interiors ...

disgusting pop music. I mean, I really liked the Stones but much
of the other stuff, yuck. Also, I doggedly stuck to cotton shirts,
mostly the lumberjack style, listened to country music and Wolfman Jack,
and avoided "modern" plastic stuff like the plague. It's still the same
except that Wolfman Jack ain't around anymore.

"I'm a lumberjack and I'm OK,
I sleep all night and I work all day ..."

--
Nicholas O. Lindan, Cleveland, Ohio
Consulting Engineer: Electronics; Informatics; Photonics.
Remove spaces etc. to reply: n o lindan at net com dot com
psst.. want to buy an f-stop timer? nolindan.com/da/fstop/

 

[Joerg]

Hi Ken,

Many of the micros on the market today can get by without a crystal unless
you want a very accurate frequency.


Then a resonator can be used, or R and C as Nicholas suggested. It'll

still be an additional 5 Cents or so. Just nitpicking ;-)

Regards, Joerg

http://www.analogconsultants.com

 

[Ken Smith]

In article <dqW9d.13722$Vm1.9239@newsread3.news.atl.earthlink.net>,
Nicholas O. Lindan <see@sig.com> wrote:
[...]

Using the AC line as a timebase keeps integrated measurements - say from a
V/F - synchronized with the power line hum - you can get 70db transverse
power line noise rejection, for free!

... and get the clock to read 24.000 hours in a day without a crystal
--
--
kensmith@rahul.net forging knowledge

 

[Ken Smith]

In article <zMW9d.8853$nj.8736@newssvr13.news.prodigy.com>,
Joerg <notthisjoergsch@removethispacbell.net> wrote:

Hi Ken,

Many of the micros on the market today can get by without a crystal unless
you want a very accurate frequency.


Then a resonator can be used, or R and C as Nicholas suggested. It'll
still be an additional 5 Cents or so. Just nitpicking ;-)

If you use the Cygnal one or, I think, some of the PICs, no external parts
are needed at all.

--
--
kensmith@rahul.net forging knowledge

 

[Joerg]

Hi Ken,

Using the AC line as a timebase keeps integrated measurements - say from a
V/F - synchronized with the power line hum - you can get 70db transverse
power line noise rejection, for free!



.. and get the clock to read 24.000 hours in a day without a crystal


Depends on where you live. We had times here in California where the day

had only 18 hours according to the 60Hz cycle count. The other six hours
were candle light and battery time.

Regards, Joerg

http://www.analogconsultants.com

 

[Ken Smith]

In article <oS0ad.9398$nj.8728@newssvr13.news.prodigy.com>,
Joerg <notthisjoergsch@removethispacbell.net> wrote:
[....]

.. and get the clock to read 24.000 hours in a day without a crystal


Depends on where you live. We had times here in California where the day
had only 18 hours according to the 60Hz cycle count. The other six hours
were candle light and battery time.

Yes, I too am in California. They problem of keeping clocks on time when
the power fails can be real trouble. I have about 8 I need to reset and
each has a different procedure for doing it.

One idea:

Let the chip always run on the internal oscillator. Use software to work
out the average period, in terms of machine cycles, of the mains.
Calibrate the fractional divider from the machine cycles based on that.
If the temperature doesn't change too much during the outage, this would
hold the clock quite well.



--
--
kensmith@rahul.net forging knowledge

 

[Fred Bloggs]

PDRUNEN wrote:

Hi All,

I want to take an analog voltage, 0-5 volts and convert over to a PWM signal
with fixed period. The on time of the PWM would be based on the input voltage.

This PWM signal will travel over a opto device for isolation and then be
converted back to a analog voltage.

You /do/ know that PWM is not V-F conversion? How much accuracy is
required? 10%, 5%, 1%...

 

[Ken Smith]

In article <Zkhad.1705$6q2.197@newssvr14.news.prodigy.com>,
Joerg <notthisjoergsch@removethispacbell.net> wrote:

Hi Ken,

Let the chip always run on the internal oscillator. Use software to work
out the average period, in terms of machine cycles, of the mains.
Calibrate the fractional divider from the machine cycles based on that.
If the temperature doesn't change too much during the outage, this would
hold the clock quite well.


That could work. But in most households the furnace will quit and then
the temps rapidly change.

We were talking about California where the temperature is always between
68 and 75 and it never rains weren't we?

Yes the temperature change is a major problem with the idea. Oh well the
clock idea was just an added feature. We really don't need it.

Not in our house because we went to a
wood stove and hardly ever use the AC. Still, since we live in the hills
east of Sacramento the temp change from day to night is pretty dramatic,
30 degrees difference are pretty normal.

My house doesn't have AC (yet). I have to say "yet" because I can't stand
high temperatures.

I'd probably swallow my pride and spring for a 32KHz clock crystal and
an MSP430. These crystals are the cheapest in their class.

You could still use a PIC, just to annoy some people. Some of the PICs
have a special extral low power mode where only one timer circuit
continues to run while the rast of the chip is parked.

Now the VCR
industry still needs to figure that out as well so we don't have the old
12:00 blink-blink after every outage.

The really dumb thing is that the VCRs are usually receiving all sorts of
RF signals. It wouldn't take much added to one of them to encode the time
every few minutes.

--
--
kensmith@rahul.net forging knowledge

 

[Joerg]

Hi Ken,

That could work. But in most households the furnace will quit and then
the temps rapidly change.



We were talking about California where the temperature is always between
68 and 75 and it never rains weren't we?


That's what my wife thought before we moved here. Then it started to

snow! Now if we had to make a choice again we'd buy a home without a
pool. Too much maintenance, too little use.

My house doesn't have AC (yet). I have to say "yet" because I can't stand
high temperatures.


Before you take the plunge into your bank account check out whether a

swamp cooler would be right. It might not work in coastal regions but
they do out here in the Sierra. The difference in the electric bill is
staggering, especially since the debacle under the previous governor
which locked us into high rates for the next few lightyears.

You could still use a PIC, just to annoy some people. Some of the PICs

have a special extral low power mode where only one timer circuit
continues to run while the rast of the chip is parked.


So does the MSP. That feature is pretty cool. I used to love the 89C51

family because it has 2nd sources but we always needed some other
realtime provider if we had to send it into the pillows.

Now the VCR
industry still needs to figure that out as well so we don't have the old
12:00 blink-blink after every outage.



The really dumb thing is that the VCRs are usually receiving all sorts of
RF signals. It wouldn't take much added to one of them to encode the time
every few minutes.


There is already time encoding on many stations during the vertical

blank period. But no, the VCR isn't able to use it. I wonder why the
engineers who designed my $20 office clock were able to have it
synchronize at night to the NIST in Boulder, CO, while the $200 VCR
needs to be reprogrammed after every outage and the clock lags or leads
a few minutes after several months.

Regards, Joerg

http://www.analogconsultants.com

 

[Ken Smith]

In article <lOiad.10789$nj.6127@newssvr13.news.prodigy.com>,
Joerg <notthisjoergsch@removethispacbell.net> wrote:

Hi Ken,
[...]
Before you take the plunge into your bank account check out whether a
swamp cooler would be right. It might not work in coastal regions but
they do out here in the Sierra. The difference in the electric bill is
staggering, especially since the debacle under the previous governor
which locked us into high rates for the next few lightyears.

If I had a good cannon, I could put a round in the bay. I don't think
swamp cooling is too likely to work but I'll be sure to check into it.

So does the MSP. That feature is pretty cool. I used to love the 89C51
family because it has 2nd sources but we always needed some other
realtime provider if we had to send it into the pillows.

Lately, I like the Cygnal parts because I need the speed. They aren't low
power though.

There is already time encoding on many stations during the vertical
blank period. But no, the VCR isn't able to use it. I wonder why the
engineers who designed my $20 office clock were able to have it
synchronize at night to the NIST in Boulder, CO, while the $200 VCR
needs to be reprogrammed after every outage and the clock lags or leads
a few minutes after several months.

"when stupidity will serve as an explaination, you need look no further".

--
--
kensmith@rahul.net forging knowledge

 

[Ken Smith]

In article <41696AD4.9030100@nospam.com>,
Fred Bloggs <nospam@nospam.com> wrote:
[...]

You /do/ know that PWM is not V-F conversion? How much accuracy is
required? 10%, 5%, 1%...

Actually PWM may or may not be V-F. In the constant on-time design each
is a non-linear version of the other. In some cases, this fact can be
important ie: (a) handy (b) trouble.

(a)
The peaks on the input are important and we get to hear about them
quickly.

(b)
The average number comes out wrong because of the ripple.


--
--
kensmith@rahul.net forging knowledge