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From: Jamie on 9 May 2010 20:01
hamilton wrote:

>
> I have been asked to build a digital to analog circuit.
>
> The flow sensor:
> http://www.gemssensors.com/uploadedFiles/Literature/Spec_Sheets/FT210_1124.pdf
>
>
> has a digital pulse output proportional to the flow.
>
> I would like to create an analog detector, so when it has reached a
> minimum flow rate, a logic level is triggered.
>
> I am a firmware guy and know how to do this with a PYFMC[1].
>
> I would like to get some suggestions on how to do this in analog.
>
>
> thanks
>
> hamilton
>
> [1] Pick Your Favorite Micro Controller
Here is a frequency to Voltage converter .. Look below and see many
examples..

http://www.national.com/ds/LM/LM2907.pdf

Its old technology but it still works, especially well for what you're
doing..

for a logic level set point, you need to pass that into a schmitt
trigger buffer, or use a comparator like the LM311, LM393 with a little
(+) feed back to get a hysteresis effect.. Or! if that is over the hump
too much, you can do what I do, and that is use the trigger and
threshold inputs tied together of a 555 timer. The timer has a 1/3
ladder voltage of the Vcc, it works nicely for a RS flip flop and a
window comparator.
The timer output will give you the logic level.. There will be no
components added to this chip :)

have a good day..



From: lektric.dan on 9 May 2010 20:37
On May 9, 2:28 pm, hamilton <hamil...(a)nothere.com> wrote:
(ker-snippity...)
> has a digital pulse output proportional to the flow.
>
> I would like to create an analog detector, so when it has reached a
> minimum flow rate, a logic level is triggered.
>
> I am a firmware guy and know how to do this with a PYFMC[1].
>
> I would like to get some suggestions on how to do this in analog.
>
OK - just off the top of my head, and I'm sure others will cruely and
casually punch holes in my suggestions...

1) how about a low-pass filter feeding into a voltage comparater.

2) frequency-to-voltage converter (LM2907/2917) - might have to put a
one-shot on the front end.

3) missing pulse detector - easily made w/a 555 (again, may need a one-
shot)

4) how big does the max flow deviate from the minimum you want to
detect? Would a PLL work? The output would be the deviation, and
again, into a voltage comparator

5) the way we do it - hire a grad (or undergrad) student to watch the
flow (or indicator)

punch away...
From: who where on 9 May 2010 20:57
On Sun, 09 May 2010 13:28:51 -0600, hamilton <hamilton(a)nothere.com>
wrote:

>
>I have been asked to build a digital to analog circuit.
>
>The flow sensor:
>http://www.gemssensors.com/uploadedFiles/Literature/Spec_Sheets/FT210_1124.pdf
>
>has a digital pulse output proportional to the flow.
>
>I would like to create an analog detector, so when it has reached a
>minimum flow rate, a logic level is triggered.
>
>I am a firmware guy and know how to do this with a PYFMC[1].
>
>I would like to get some suggestions on how to do this in analog.
>
>
>thanks
>
>hamilton
>
>[1] Pick Your Favorite Micro Controller

A retriggerable monostable will provide the required functionality.
From: Spehro Pefhany on 9 May 2010 21:16
On Sun, 09 May 2010 13:28:51 -0600, the renowned hamilton
<hamilton(a)nothere.com> wrote:

>
>I have been asked to build a digital to analog circuit.
>
>The flow sensor:
>http://www.gemssensors.com/uploadedFiles/Literature/Spec_Sheets/FT210_1124.pdf
>
>has a digital pulse output proportional to the flow.
>
>I would like to create an analog detector, so when it has reached a
>minimum flow rate, a logic level is triggered.
>
>I am a firmware guy and know how to do this with a PYFMC[1].
>
>I would like to get some suggestions on how to do this in analog.
>
>
>thanks
>
>hamilton
>
>[1] Pick Your Favorite Micro Controller

A TLC555 connected as a monostable and a comparator (with
hysteresis?), plus a low-pass filter with an RC or two. Probably more
than a dozen parts.

I think I'd use a micro with 1% internal calibrated oscillator (or
maybe a 0.5% ceramic resonator) and that's about it. Writing the code
might take a bit longer than designing the analog circuit, but the
parts count reduction would probably be worth it.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff(a)interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
From: Phil Allison on 9 May 2010 22:38

"hamilton"

> I have been asked to build a digital to analog circuit.
>
> The flow sensor:
> http://www.gemssensors.com/uploadedFiles/Literature/Spec_Sheets/FT210_1124.pdf
>
> has a digital pulse output proportional to the flow.


** Small but important point - why did you call the pulse ouput "digital" ?

There is nothing digital about such a varying pulse train - it's pure
analogue.




..... Phil




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