simplified converter needed for duty cycle to voltage

M

m II

Guest
I need to simplify a 'duty cycle to voltage' circuit. The range it has
to cover are a varying 5 volt square wave pulse with a frequency range
of 40 Hertz to 400 Hertz. Once the frequency is set it stays there while
the duty cycle of the square wave is varied within the set time period.

The idea is to use a voltmeter as a percent duty cycle indicator. ie:
10.0 volts = 100 percent duty cycle. If the frequency was always
constant I think I could get away with a resistor and capacitor and just
measure the average voltage. Things become more difficult with the
variable frequency thrown in.

Any help would be welcome.

mike






--
It is hard enough to remember my opinions, without also remembering my
reasons for them!
--Friedrich Nietzsche
 
On Sunday, June 8, 2014 4:22:20 PM UTC-4, m II wrote:
I need to simplify a 'duty cycle to voltage' circuit. The range it has
to cover are a varying 5 volt square wave pulse with a frequency range
of 40 Hertz to 400 Hertz. Once the frequency is set it stays there while
the duty cycle of the square wave is varied within the set time period.

The idea is to use a voltmeter as a percent duty cycle indicator. ie:
10.0 volts = 100 percent duty cycle. If the frequency was always
constant I think I could get away with a resistor and capacitor and just
measure the average voltage. Things become more difficult with the
variable frequency thrown in.
Click to expand...

You could have it fire a one-shot, with the time picked to give
full scale at 400 Hz.

George H.
Any help would be welcome.



mike













--

It is hard enough to remember my opinions, without also remembering my

reasons for them!

--Friedrich Nietzsche
Click to expand...
 
On 2014-06-08, m II <C@in.the.hat> wrote:
I need to simplify a 'duty cycle to voltage' circuit. The range it has
to cover are a varying 5 volt square wave pulse with a frequency range
of 40 Hertz to 400 Hertz. Once the frequency is set it stays there while
the duty cycle of the square wave is varied within the set time period.

The idea is to use a voltmeter as a percent duty cycle indicator. ie:
10.0 volts = 100 percent duty cycle. If the frequency was always
constant I think I could get away with a resistor and capacitor and just
measure the average voltage. Things become more difficult with the
variable frequency thrown in.

Any help would be welcome.
Click to expand...

5V= 100% duty cycle (or 1V=100%) are easier to arrange

(because 100% is indisctuguishable from 5VDC)

if you pick a resistor and capacitor that works OK at 40Hz
it'll work even better at 400Hz


--
umop apisdn


--- news://freenews.netfront.net/ - complaints: news@netfront.net ---
 
On Sunday, June 8, 2014 1:22:20 PM UTC-7, m II wrote:
I need to simplify a 'duty cycle to voltage' circuit. The range it has
to cover are a varying 5 volt square wave pulse with a frequency range
of 40 Hertz to 400 Hertz. Once the frequency is set it stays there while
the duty cycle of the square wave is varied within the set time period.
Click to expand...

Of course, a moving-needle meter will read 5V at 100%, 0V at 0%; the
mass of the needle prevents it from following the frequency.

That's assuming your square wave is 0V to 5V, and that the
needed accuracy isn't better than those two known voltages.
 
On Sun, 8 Jun 2014 17:08:03 -0700 (PDT), George Herold <gherold@teachspin.com>
wrote:

On Sunday, June 8, 2014 4:22:20 PM UTC-4, m II wrote:
I need to simplify a 'duty cycle to voltage' circuit. The range it has
to cover are a varying 5 volt square wave pulse with a frequency range
of 40 Hertz to 400 Hertz. Once the frequency is set it stays there while
the duty cycle of the square wave is varied within the set time period.

The idea is to use a voltmeter as a percent duty cycle indicator. ie:
10.0 volts = 100 percent duty cycle. If the frequency was always
constant I think I could get away with a resistor and capacitor and just
measure the average voltage. Things become more difficult with the
variable frequency thrown in.

You could have it fire a one-shot, with the time picked to give
full scale at 400 Hz.
Click to expand...

If you can fire on both edges, it's easier to filter the ripple.

https://dl.dropboxusercontent.com/u/53724080/Circuits/DoubleTach.jpg



--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation
 
On Monday, June 9, 2014 7:39:39 PM UTC-4, Jim Thompson wrote:
On Mon, 09 Jun 2014 08:34:39 -0700, John Larkin

jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Sun, 8 Jun 2014 17:08:03 -0700 (PDT), George Herold <gherold@teachspin.com

wrote:



On Sunday, June 8, 2014 4:22:20 PM UTC-4, m II wrote:
I need to simplify a 'duty cycle to voltage' circuit. The range it has
to cover are a varying 5 volt square wave pulse with a frequency range
of 40 Hertz to 400 Hertz. Once the frequency is set it stays there while
the duty cycle of the square wave is varied within the set time period.

The idea is to use a voltmeter as a percent duty cycle indicator. ie:
10.0 volts = 100 percent duty cycle. If the frequency was always
constant I think I could get away with a resistor and capacitor and just
measure the average voltage. Things become more difficult with the
variable frequency thrown in.



You could have it fire a one-shot, with the time picked to give
full scale at 400 Hz.


If you can fire on both edges, it's easier to filter the ripple.
snip

As I read it, the OP wants a voltage output proportional to duty
cycle, _NOT_proportional_to_frequency_, which is what a tachometer
circuit does.
Click to expand...

Oops, my fault. Ahh. well of course the OP just needs the RC low pass.
I don't understand about the changing frequency.(?)

George H.
...Jim Thompson

--

| James E.Thompson | mens |

| Analog Innovations | et |

| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |

| San Tan Valley, AZ 85142 Skype: skypeanalog | |

| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |

| E-mail Icon at http://www.analog-innovations.com | 1962 |



I love to cook with wine. Sometimes I even put it in the food.
Click to expand...
 
You put a resistor from it to a capacitor to ground.

Like a 10 K going to a 47 uF.

you got other requirement like response time anmd all that ? State them. Otherwise that will work, if you are not pulling any current and don't care about efficiency.

If you want efficiency use a coil instead fo a resistor. It also damps up the DC output better.
 
"Things become more difficult with the
variable frequency thrown in. "
Click to expand...

OK, 100K and 100 UF then. Should work fine as long as the meter doesn't load.

The engineering question here is for one - how fast do you want it to respond ?

The sinmple RC will do exactly what you want, no doubt. The voltage of course has to be tightly regulated. IF you can rescale the readout, it can be any voltage, but it still has to stay right on the money or the reading will be off.

At 40 Hz, a 10 K into a 47 uF wil make so close to DC it will be fine. It will also take (2tt/t/whatever time constant) to respond to a change. how long do you want to wait ?

You could use a megohm and a 160,000 uF, but it would take about a week to respond.
 
On Mon, 09 Jun 2014 08:34:39 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Sun, 8 Jun 2014 17:08:03 -0700 (PDT), George Herold <gherold@teachspin.com
wrote:

On Sunday, June 8, 2014 4:22:20 PM UTC-4, m II wrote:
I need to simplify a 'duty cycle to voltage' circuit. The range it has
to cover are a varying 5 volt square wave pulse with a frequency range
of 40 Hertz to 400 Hertz. Once the frequency is set it stays there while
the duty cycle of the square wave is varied within the set time period.

The idea is to use a voltmeter as a percent duty cycle indicator. ie:
10.0 volts = 100 percent duty cycle. If the frequency was always
constant I think I could get away with a resistor and capacitor and just
measure the average voltage. Things become more difficult with the
variable frequency thrown in.

You could have it fire a one-shot, with the time picked to give
full scale at 400 Hz.


If you can fire on both edges, it's easier to filter the ripple.

https://dl.dropboxusercontent.com/u/53724080/Circuits/DoubleTach.jpg
Click to expand...

As I read it, the OP wants a voltage output proportional to duty
cycle, _NOT_proportional_to_frequency_, which is what a tachometer
circuit does.

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
 
On Mon, 9 Jun 2014 17:22:37 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

On Monday, June 9, 2014 7:39:39 PM UTC-4, Jim Thompson wrote:
On Mon, 09 Jun 2014 08:34:39 -0700, John Larkin

jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Sun, 8 Jun 2014 17:08:03 -0700 (PDT), George Herold <gherold@teachspin.com

wrote:



On Sunday, June 8, 2014 4:22:20 PM UTC-4, m II wrote:
I need to simplify a 'duty cycle to voltage' circuit. The range it has
to cover are a varying 5 volt square wave pulse with a frequency range
of 40 Hertz to 400 Hertz. Once the frequency is set it stays there while
the duty cycle of the square wave is varied within the set time period.

The idea is to use a voltmeter as a percent duty cycle indicator. ie:
10.0 volts = 100 percent duty cycle. If the frequency was always
constant I think I could get away with a resistor and capacitor and just
measure the average voltage. Things become more difficult with the
variable frequency thrown in.



You could have it fire a one-shot, with the time picked to give
full scale at 400 Hz.


If you can fire on both edges, it's easier to filter the ripple.
snip

As I read it, the OP wants a voltage output proportional to duty
cycle, _NOT_proportional_to_frequency_, which is what a tachometer
circuit does.

Oops, my fault. Ahh. well of course the OP just needs the RC low pass.
I don't understand about the changing frequency.(?)

George H.


...Jim Thompson

[snip]
Click to expand...

Who knows? I think it's just the range of input frequencies the OP
has to contend with.

You could do it digitally, with a uP. Count the on and off times,
then do the math... then feed a DAC if your mind-set is to have an
analog output.

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
 
On Tuesday, June 10, 2014 9:10:49 AM UTC-7, petrus bitbyter wrote:

On Sunday, June 8, 2014 4:22:20 PM UTC-4, m II wrote:

I need to simplify a 'duty cycle to voltage' circuit.

When even the king of analog advises a digital solution what other
possibilities may exist? I agree, the most simple solution is a micro,
Click to expand...

NO! Nothing with a microprocessor is really simple, and especially
nothing that requires real-time performance.

A flip-flop and two sample-hold integrators will give you one-cycle
response time, if that's required. Resistor/capacitor/op amp makes
an integrator, and the flip flop operates analog switches to enable
one integrator input, with output disconnected, while the other input
floats, but has its output-connected.
Two discharge transistors are operated from the sharp edges
of the flip-flop output (so each input-connected integrator starts
with a discharged hold capacitor) in the obvious way.

If you can just enable/wait/read the output, it only takes one op amp,
and fewer switches. That would be a fairly good way to do things
if a microprocessor is doing the readout.
 
"Jim Thompson" schreef in bericht
news:elkcp9pqnp4ceolemcm2rs76e5eit36n1q@4ax.com...

On Mon, 9 Jun 2014 17:22:37 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

On Monday, June 9, 2014 7:39:39 PM UTC-4, Jim Thompson wrote:
On Mon, 09 Jun 2014 08:34:39 -0700, John Larkin

jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Sun, 8 Jun 2014 17:08:03 -0700 (PDT), George Herold
gherold@teachspin.com

wrote:



On Sunday, June 8, 2014 4:22:20 PM UTC-4, m II wrote:
I need to simplify a 'duty cycle to voltage' circuit. The range it
has
to cover are a varying 5 volt square wave pulse with a frequency
range
of 40 Hertz to 400 Hertz. Once the frequency is set it stays there
while
the duty cycle of the square wave is varied within the set time
period.

The idea is to use a voltmeter as a percent duty cycle indicator. ie:
10.0 volts = 100 percent duty cycle. If the frequency was always
constant I think I could get away with a resistor and capacitor and
just
measure the average voltage. Things become more difficult with the
variable frequency thrown in.



You could have it fire a one-shot, with the time picked to give
full scale at 400 Hz.


If you can fire on both edges, it's easier to filter the ripple.
snip

As I read it, the OP wants a voltage output proportional to duty
cycle, _NOT_proportional_to_frequency_, which is what a tachometer
circuit does.

Oops, my fault. Ahh. well of course the OP just needs the RC low pass.
I don't understand about the changing frequency.(?)

George H.


...Jim Thompson

[snip]
Click to expand...

Who knows? I think it's just the range of input frequencies the OP
has to contend with.

You could do it digitally, with a uP. Count the on and off times,
then do the math... then feed a DAC if your mind-set is to have an
analog output.

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.



***

When even the king of analog advises a digital solution what other
possibilities may exist? I agree, the most simple solution is a micro,
preferable one with a build in DA-converter. As this type of converters
often provide a 0-5V output, you will need an opamp to amplify that
output... and a program. There are lots of micros available with or without
DA, and dozens of separate DA-converters if you want one. But the learning
curve will be prety steep. Requires lots of time. Maybe too much time for a
one-off. So I propose a digital-analog solution.

Divide the 40-400Hz frequency range in eight or sixteen subranges. Each of
that subranges should be handled by a separate RC-combination. To select the
required RC, take an 8-bits counter that runs with a 1kHz clock to measure
the current period time. The output of that counter will drive the selector.
Off course, you wil need a little bit of control logic but that should not
be that difficult.

petrus bitbyter
 
On Tue, 10 Jun 2014 18:10:49 +0200, "petrus bitbyter"
<petrus.bitbyter@hotmail.com> wrote:

"Jim Thompson" schreef in bericht
news:elkcp9pqnp4ceolemcm2rs76e5eit36n1q@4ax.com...

On Mon, 9 Jun 2014 17:22:37 -0700 (PDT), George Herold
gherold@teachspin.com> wrote:

On Monday, June 9, 2014 7:39:39 PM UTC-4, Jim Thompson wrote:
On Mon, 09 Jun 2014 08:34:39 -0700, John Larkin

jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Sun, 8 Jun 2014 17:08:03 -0700 (PDT), George Herold
gherold@teachspin.com

wrote:



On Sunday, June 8, 2014 4:22:20 PM UTC-4, m II wrote:
I need to simplify a 'duty cycle to voltage' circuit. The range it
has
to cover are a varying 5 volt square wave pulse with a frequency
range
of 40 Hertz to 400 Hertz. Once the frequency is set it stays there
while
the duty cycle of the square wave is varied within the set time
period.

The idea is to use a voltmeter as a percent duty cycle indicator. ie:
10.0 volts = 100 percent duty cycle. If the frequency was always
constant I think I could get away with a resistor and capacitor and
just
measure the average voltage. Things become more difficult with the
variable frequency thrown in.



You could have it fire a one-shot, with the time picked to give
full scale at 400 Hz.


If you can fire on both edges, it's easier to filter the ripple.
snip

As I read it, the OP wants a voltage output proportional to duty
cycle, _NOT_proportional_to_frequency_, which is what a tachometer
circuit does.

Oops, my fault. Ahh. well of course the OP just needs the RC low pass.
I don't understand about the changing frequency.(?)

George H.


...Jim Thompson

[snip]

Who knows? I think it's just the range of input frequencies the OP
has to contend with.

You could do it digitally, with a uP. Count the on and off times,
then do the math... then feed a DAC if your mind-set is to have an
analog output.

...Jim Thompson

When even the king of analog advises a digital solution what other
possibilities may exist? I agree, the most simple solution is a micro,
preferable one with a build in DA-converter. As this type of converters
often provide a 0-5V output, you will need an opamp to amplify that
output... and a program. There are lots of micros available with or without
DA, and dozens of separate DA-converters if you want one. But the learning
curve will be prety steep. Requires lots of time. Maybe too much time for a
one-off. So I propose a digital-analog solution.

Divide the 40-400Hz frequency range in eight or sixteen subranges. Each of
that subranges should be handled by a separate RC-combination. To select the
required RC, take an 8-bits counter that runs with a 1kHz clock to measure
the current period time. The output of that counter will drive the selector.
Off course, you wil need a little bit of control logic but that should not
be that difficult.

petrus bitbyter
Click to expand...

I also had twisted thoughts... Use dual slope A-D techniques to
convert period to a voltage, likewise convert on time to a voltage...
add nasty analog manipulation and get laughed off the group >:-}

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
 
On 2014-06-10, Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:
On Tue, 10 Jun 2014 18:10:49 +0200, "petrus bitbyter"
petrus.bitbyter@hotmail.com> wrote:


I also had twisted thoughts... Use dual slope A-D techniques to
convert period to a voltage, likewise convert on time to a voltage...
add nasty analog manipulation and get laughed off the group >:-}
Click to expand...

no manipulation, just use a crossed-coil meter movement -
perhaps a re-purposed fuel gauge.


--
umop apisdn


--- news://freenews.netfront.net/ - complaints: news@netfront.net ---
 
On 11 Jun 2014 12:48:38 GMT, Jasen Betts <jasen@xnet.co.nz> wrote:

On 2014-06-10, Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:
On Tue, 10 Jun 2014 18:10:49 +0200, "petrus bitbyter"
petrus.bitbyter@hotmail.com> wrote:


I also had twisted thoughts... Use dual slope A-D techniques to
convert period to a voltage, likewise convert on time to a voltage...
add nasty analog manipulation and get laughed off the group >:-}

no manipulation, just use a crossed-coil meter movement -
perhaps a re-purposed fuel gauge.
Click to expand...

Good point... nice gadgets. I once was tasked with designing a driver
to linearize such a gauge.... equal angles for equal input voltage
increments (45 years ago :)

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
 
On Sun, 08 Jun 2014 14:22:20 -0600, m II <C@in.the.hat> wrote:

I need to simplify a 'duty cycle to voltage' circuit. The range it has
to cover are a varying 5 volt square wave pulse with a frequency range
of 40 Hertz to 400 Hertz. Once the frequency is set it stays there while
the duty cycle of the square wave is varied within the set time period.

The idea is to use a voltmeter as a percent duty cycle indicator. ie:
10.0 volts = 100 percent duty cycle. If the frequency was always
constant I think I could get away with a resistor and capacitor and just
measure the average voltage. Things become more difficult with the
variable frequency thrown in.

Any help would be welcome.

mike
Click to expand...

---
Mike,

I have a circuit with a duty cycle that you can set at any frequency
within your 40 to 400Hz band, then change the frequency and the duty
cycle remains constant.

I can't give it away, but if you're interested email me.

John Fields
 
On Sunday, June 15, 2014 11:44:09 AM UTC-7, m II wrote:

At first I thought of an analog voltmeter with a centered needle. At 50
percent duty cycle, that would probably zero the needle. Then I
discovered the local electronics place wanted over ninety dollars for
the thing.
Click to expand...

You probably want 'duty cycle' markings and other customizations, the
off-the-shelf meter price isn't indicative of what it'd be in production.
Center-zero can be induced by adding a bias current source to
any meter (and the old moving-needle meter is still available at about $5 USD).

<http://usd.dx.com/product/dc-0-1ma-square-panel-mounting-analog-amp-current-meter-ammeter-white-901164446>
 
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