Driver to drive?

[Lasse Langwadt Christense]

Den tirsdag den 4. november 2014 20.24.20 UTC+1 skrev Tim Wescott:

On Tue, 04 Nov 2014 17:38:01 +0100, blisca wrote:

Hi to all,

often i have to measure the current absorbed by small circuits,in
battery appplications Normally i deal with consumptions big as 20mA in
run mode and 2uA in sleep mode.

One method that sometimes i use is to desconnect the battery,leaving the
circuit feeded only by a 10,000 uF capacitor,seldom and quickly measured
by an high impedence multimeter,(of course not a 10 Mohm oscilloscope
probe).Measuring the difference in voltage at a specified times i can
calculate the consumption.The cap was previously measured,to avoid
tolerance error.

More often i need a more immediate measurement,so i feed the circuit by
a commutator switch,in parallel to 1,10 and 100 ohm shunt resistors.
The latter is constantly inserted so that the circuit is not completely
relying on itself during commutations.
When the uc goes to sleep and i need to have an hopefully realistic
rading of few uA i switch on the 100 ohm shunt,the voltage drop between
battery and circuit is below the mV,therefore irrelevant.
The voltage is read by a 6 and half digit DMM via a 60cm(2 ft)twisted
wire.

Is this a good method or others can be better?

Is there any advantage using an instrumentation op amp as buffer or
amplifier, wired very closely to the shunt?

Many thanks for your attention

Diego

I'm taking the liberty of cross-posting this to sci.electronics.design,
because this is really an electronics question, not an embedded question.
I think you'll get more answers from there, and many of them will even be
good ones.

I think your commutation idea will suffer in accuracy if the load is
fairly stiff in voltage -- like if you're driving a capacitor. In that
case the current with the low resistance switched in will be higher than
without.

If the circuit is otherwise isolated, the best way to do the measurement
may be to put your 100 ohm resistor between the circuit ground and the
negative terminal of the battery, then amplify its voltage by 10 or 100
using a chopper-stabilized op-amp. Then you can just read the voltage and
scale it appropriately to current.

get one of Dave Jones uCurrent

http://eevblog.myshopify.com/products/ucurrent


-Lasse

 

[Tim Wescott]

On Tue, 04 Nov 2014 17:38:01 +0100, blisca wrote:

Hi to all,

often i have to measure the current absorbed by small circuits,in
battery appplications Normally i deal with consumptions big as 20mA in
run mode and 2uA in sleep mode.

One method that sometimes i use is to desconnect the battery,leaving the
circuit feeded only by a 10,000 uF capacitor,seldom and quickly measured
by an high impedence multimeter,(of course not a 10 Mohm oscilloscope
probe).Measuring the difference in voltage at a specified times i can
calculate the consumption.The cap was previously measured,to avoid
tolerance error.

More often i need a more immediate measurement,so i feed the circuit by
a commutator switch,in parallel to 1,10 and 100 ohm shunt resistors.
The latter is constantly inserted so that the circuit is not completely
relying on itself during commutations.
When the uc goes to sleep and i need to have an hopefully realistic
rading of few uA i switch on the 100 ohm shunt,the voltage drop between
battery and circuit is below the mV,therefore irrelevant.
The voltage is read by a 6 and half digit DMM via a 60cm(2 ft)twisted
wire.

Is this a good method or others can be better?

Is there any advantage using an instrumentation op amp as buffer or
amplifier, wired very closely to the shunt?

Many thanks for your attention

Diego

I'm taking the liberty of cross-posting this to sci.electronics.design,
because this is really an electronics question, not an embedded question.
I think you'll get more answers from there, and many of them will even be
good ones.

I think your commutation idea will suffer in accuracy if the load is
fairly stiff in voltage -- like if you're driving a capacitor. In that
case the current with the low resistance switched in will be higher than
without.

If the circuit is otherwise isolated, the best way to do the measurement
may be to put your 100 ohm resistor between the circuit ground and the
negative terminal of the battery, then amplify its voltage by 10 or 100
using a chopper-stabilized op-amp. Then you can just read the voltage and
scale it appropriately to current.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

 

[George Herold]

On Tuesday, November 4, 2014 3:03:26 PM UTC-5, George Herold wrote:

On Tuesday, November 4, 2014 2:24:20 PM UTC-5, Tim Wescott wrote:
On Tue, 04 Nov 2014 17:38:01 +0100, blisca wrote:

Hi to all,

often i have to measure the current absorbed by small circuits,in
battery appplications Normally i deal with consumptions big as 20mA in
run mode and 2uA in sleep mode.

One method that sometimes i use is to desconnect the battery,leaving the
circuit feeded only by a 10,000 uF capacitor,seldom and quickly measured
by an high impedence multimeter,(of course not a 10 Mohm oscilloscope
probe).Measuring the difference in voltage at a specified times i can
calculate the consumption.The cap was previously measured,to avoid
tolerance error.

More often i need a more immediate measurement,so i feed the circuit by
a commutator switch,in parallel to 1,10 and 100 ohm shunt resistors.
The latter is constantly inserted so that the circuit is not completely
relying on itself during commutations.
When the uc goes to sleep and i need to have an hopefully realistic
rading of few uA i switch on the 100 ohm shunt,the voltage drop between
battery and circuit is below the mV,therefore irrelevant.
The voltage is read by a 6 and half digit DMM via a 60cm(2 ft)twisted
wire.

Is this a good method or others can be better?

Is there any advantage using an instrumentation op amp as buffer or
amplifier, wired very closely to the shunt?

Many thanks for your attention

Diego

I'm taking the liberty of cross-posting this to sci.electronics.design,
because this is really an electronics question, not an embedded question.
I think you'll get more answers from there, and many of them will even be
good ones.

I think your commutation idea will suffer in accuracy if the load is
fairly stiff in voltage -- like if you're driving a capacitor. In that
case the current with the low resistance switched in will be higher than
without.

If the circuit is otherwise isolated, the best way to do the measurement
may be to put your 100 ohm resistor between the circuit ground and the
negative terminal of the battery, then amplify its voltage by 10 or 100
using a chopper-stabilized op-amp. Then you can just read the voltage and
scale it appropriately to current.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I was going to suggest a TIA (trans impedance amp.) opamp in the ground return line, maybe with a few R's for different ranges.

I put one together to measure semi conductor I-V and I've used it for a few different things now. (AC resistance of tap water a few weeks ago.)

George H.

Maybe with a switch to short the input when you switch R's.
(would current interuptus wake up the uC?)

 

[Syd Rumpo]

On 04/11/2014 20:03, George Herold wrote:

On Tuesday, November 4, 2014 2:24:20 PM UTC-5, Tim Wescott wrote:
On Tue, 04 Nov 2014 17:38:01 +0100, blisca wrote:

Hi to all,

often i have to measure the current absorbed by small circuits,in
battery appplications Normally i deal with consumptions big as 20mA in
run mode and 2uA in sleep mode.

One method that sometimes i use is to desconnect the battery,leaving the
circuit feeded only by a 10,000 uF capacitor,seldom and quickly measured
by an high impedence multimeter,(of course not a 10 Mohm oscilloscope
probe).Measuring the difference in voltage at a specified times i can
calculate the consumption.The cap was previously measured,to avoid
tolerance error.

More often i need a more immediate measurement,so i feed the circuit by
a commutator switch,in parallel to 1,10 and 100 ohm shunt resistors.
The latter is constantly inserted so that the circuit is not completely
relying on itself during commutations.
When the uc goes to sleep and i need to have an hopefully realistic
rading of few uA i switch on the 100 ohm shunt,the voltage drop between
battery and circuit is below the mV,therefore irrelevant.
The voltage is read by a 6 and half digit DMM via a 60cm(2 ft)twisted
wire.

Is this a good method or others can be better?

Is there any advantage using an instrumentation op amp as buffer or
amplifier, wired very closely to the shunt?

Many thanks for your attention

Diego

I'm taking the liberty of cross-posting this to sci.electronics.design,
because this is really an electronics question, not an embedded question.
I think you'll get more answers from there, and many of them will even be
good ones.

I think your commutation idea will suffer in accuracy if the load is
fairly stiff in voltage -- like if you're driving a capacitor. In that
case the current with the low resistance switched in will be higher than
without.

If the circuit is otherwise isolated, the best way to do the measurement
may be to put your 100 ohm resistor between the circuit ground and the
negative terminal of the battery, then amplify its voltage by 10 or 100
using a chopper-stabilized op-amp. Then you can just read the voltage and
scale it appropriately to current.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I was going to suggest a TIA (trans impedance amp.) opamp in the ground return line, maybe with a few R's for different ranges.

I put one together to measure semi conductor I-V and I've used it for a few different things now. (AC resistance of tap water a few weeks ago.)

George H.

For a non-varying current, I would perhaps use a series resistor (or
pot) in the supply rail with a multimeter across and adjust to get, say,
around 100mV drop, then substitute the device under test with a second
resistor - maybe another pot - to achieve the same drop across the
series resistor.


Cheers
--
Syd

 

[josephkk]

On Tue, 04 Nov 2014 13:24:15 -0600, Tim Wescott
<seemywebsite@myfooter.really> wrote:

On Tue, 04 Nov 2014 17:38:01 +0100, blisca wrote:

Hi to all,

often i have to measure the current absorbed by small circuits,in
battery appplications Normally i deal with consumptions big as 20mA in
run mode and 2uA in sleep mode.

One method that sometimes i use is to desconnect the battery,leaving the
circuit feeded only by a 10,000 uF capacitor,seldom and quickly measured
by an high impedence multimeter,(of course not a 10 Mohm oscilloscope
probe).Measuring the difference in voltage at a specified times i can
calculate the consumption.The cap was previously measured,to avoid
tolerance error.

More often i need a more immediate measurement,so i feed the circuit by
a commutator switch,in parallel to 1,10 and 100 ohm shunt resistors.
The latter is constantly inserted so that the circuit is not completely
relying on itself during commutations.
When the uc goes to sleep and i need to have an hopefully realistic
rading of few uA i switch on the 100 ohm shunt,the voltage drop between
battery and circuit is below the mV,therefore irrelevant.
The voltage is read by a 6 and half digit DMM via a 60cm(2 ft)twisted
wire.

Is this a good method or others can be better?

Is there any advantage using an instrumentation op amp as buffer or
amplifier, wired very closely to the shunt?

Many thanks for your attention

Diego

I'm taking the liberty of cross-posting this to sci.electronics.design,
because this is really an electronics question, not an embedded question.
I think you'll get more answers from there, and many of them will even be
good ones.

I think your commutation idea will suffer in accuracy if the load is
fairly stiff in voltage -- like if you're driving a capacitor. In that
case the current with the low resistance switched in will be higher than
without.

If the circuit is otherwise isolated, the best way to do the measurement
may be to put your 100 ohm resistor between the circuit ground and the
negative terminal of the battery, then amplify its voltage by 10 or 100
using a chopper-stabilized op-amp. Then you can just read the voltage and
scale it appropriately to current.

OPs method makes a lot of sense where the average current is a lot lower
than the maximum current. Many low power uPs have sleep modes where they
only run about 1 percent of the time; the rest of the time only timers and
such run. Greatly reducing average power and making measurement much more
difficult.

?-)

 

[Bill Sloman]

On Friday, 7 November 2014 05:45:24 UTC+11, rickman wrote:

On 11/6/2014 1:36 PM, Michael A. Terrell wrote:

I just spoke to John Fields. He said he was tired of the bickering on
the electronics newsgroups, and quit using them. He knows his website is
down, and said he hasn't got around to redoing it.

I know the feeling. But there are groups without so much of the crap.
This is one of the worst.

Sci.electronics.design is one of the most active usegroups.

I check out what's going on a couple of times a day, because I'm interested in the kind of stuff that gets posted.

The most interesting stuff for me is the real electronics, and I don't get that in real life - despite the fact that I'm treasurer of the NSW branch of the IEEE, I still have very little contact with people who do my kind of electronics, while people who do post here quite frequently.

There is other stuff that I'm interested in - politics, anthropogenic global warming - and when a post comes up about that I react to it.

What John Fields objects to as bickering is just poorly disciplined debate - some of our regular posters don't actually understand what's involved in civilised discussion (and I'm certainly not as civilised as I might be) so we get John Larkin parading his injured ego a little more often than he should, and krw parading his unexamined certainties a lot more often than is useful.

The noise level is high, but there's also quite a bit of signal.

If I knew a better usegroup, I'd go to it.

--
Bill Sloman, Sydney

 

[Bill Sloman]

On Friday, 7 November 2014 06:52:10 UTC+11, DecadentLinuxUserNumeroUno wrote:

On Thu, 06 Nov 2014 13:44:47 -0500, rickman <gnuarm@gmail.com> Gave us:

On 11/6/2014 1:36 PM, Michael A. Terrell wrote:

I just spoke to John Fields. He said he was tired of the bickering on
the electronics newsgroups, and quit using them. He knows his website is
down, and said he hasn't got around to redoing it.

I know the feeling. But there are groups without so much of the crap.
This is one of the worst.

<snip>

> The Zimmerman complex abounds.

Or would, if it existed.

One can learn about the human condition so much by watching a modern TV
show, like "The Walking Dead".

Probably not.

John Lennon said it best though.

"A working class hero is something to be."

I'll let you figure out what the next line is, and what it means about
you.

http://www.metrolyrics.com/working-class-hero-lyrics-john-lennon.html

Since the quoted line is the refrain, and is thus followed by a variety of different lines, DecadentLinuxUserNumeroUno is being as off-the-wall as ever.

--
Bill Sloman, Sydney

 

[Bill Sloman]

On Friday, 7 November 2014 08:00:58 UTC+11, DecadentLinuxUserNumeroUno wrote:

On Thu, 6 Nov 2014 12:56:40 -0800 (PST), Bill Sloman
bill.sloman@gmail.com> Gave us:
On Friday, 7 November 2014 06:52:10 UTC+11, DecadentLinuxUserNumeroUno
wrote:
On Thu, 06 Nov 2014 13:44:47 -0500, rickman <gnuarm@gmail.com> Gave us:
On 11/6/2014 1:36 PM, Michael A. Terrell wrote:

<snip>

John Lennon said it best though.

"A working class hero is something to be."

I'll let you figure out what the next line is, and what it means about
you.

http://www.metrolyrics.com/working-class-hero-lyrics-john-lennon.html

Since the quoted line is the refrain, and is thus followed by a variety of different lines, DecadentLinuxUserNumeroUno is being as off-the-wall as ever.

It is more than a little obvious which line I was referring to, Usenet
peasant.

Really? One of the symptoms of mental illness is the delusion that one's thought processes are transparent to others. Your thinking - if one can dignify what you post as "thinking" - is decidedly obscure.

You'd probably be more highly though of if you left it that way - as an obscure creep rather than a comical one.

--
Bill Sloman, Sydney

 

[Bill Sloman]

On Friday, 7 November 2014 08:49:08 UTC+11, DecadentLinuxUserNumeroUno wrote:

On Thu, 6 Nov 2014 13:19:34 -0800 (PST), Bill Sloman
bill.sloman@gmail.com> Gave us:
On Friday, 7 November 2014 08:00:58 UTC+11, DecadentLinuxUserNumeroUno wrote:
It is more than a little obvious which line I was referring to, Usenet
peasant.

Really?

Absolutely, idiot.

Moronic assertion doesn't make it true.

Tell us which line you had in mind, and we might have reason to believe you - though I doubt it.

<snipped pointless twaddle>

--
Bill Sloman, Sydney

 

[Bill Sloman]

On Friday, 7 November 2014 08:38:18 UTC+11, Jim Thompson wrote:

On Thu, 06 Nov 2014 11:51:47 -0800, DecadentLinuxUserNumeroUno
DLU1@DecadentLinuxUser.org> wrote:
On Thu, 06 Nov 2014 13:44:47 -0500, rickman <gnuarm@gmail.com> Gave us:
On 11/6/2014 1:36 PM, Michael A. Terrell wrote:

I just spoke to John Fields. He said he was tired of the bickering on
the electronics newsgroups, and quit using them. He knows his website is
down, and said he hasn't got around to redoing it.

I know the feeling. But there are groups without so much of the crap.
This is one of the worst.

<snipped DecadentLinuxUserNumeroUno being as off the wall as ever>

> Rickman is one of the worst offenders... all mouth and no brain.

As if Jim-out-of-touch-with-reality-Thompson could recognise intellectual content ... him complaining about anybody else being all mouth is also entertaining.

--
Bill Sloman, Sydney

 

[George Herold]

On Thursday, November 6, 2014 1:37:10 PM UTC-5, Michael Terrell wrote:

I just spoke to John Fields. He said he was tired of the bickering on
the electronics newsgroups, and quit using them. He knows his website is
down, and said he hasn't got around to redoing it.


--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.

Thanks for checking Michael.

George H.

 

[Michael A. Terrell]

I just spoke to John Fields. He said he was tired of the bickering on
the electronics newsgroups, and quit using them. He knows his website is
down, and said he hasn't got around to redoing it.


--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.

 

[rickman]

On 11/6/2014 1:36 PM, Michael A. Terrell wrote:

I just spoke to John Fields. He said he was tired of the bickering on
the electronics newsgroups, and quit using them. He knows his website is
down, and said he hasn't got around to redoing it.

I know the feeling. But there are groups without so much of the crap.
This is one of the worst.

--

Rick

 

[Tim Wescott]

On Thu, 06 Nov 2014 13:44:47 -0500, rickman wrote:

On 11/6/2014 1:36 PM, Michael A. Terrell wrote:

I just spoke to John Fields. He said he was tired of the bickering
on
the electronics newsgroups, and quit using them. He knows his website
is down, and said he hasn't got around to redoing it.

I know the feeling. But there are groups without so much of the crap.
This is one of the worst.

Oh, heavens Rick -- you need to become an amateur machinist and subscribe
to rec.crafts.metalworking.

Then you'll see how civil and on-topic this group really is!

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

 

[rickman]

On 11/6/2014 1:49 PM, Tim Wescott wrote:

On Thu, 06 Nov 2014 13:44:47 -0500, rickman wrote:

On 11/6/2014 1:36 PM, Michael A. Terrell wrote:

I just spoke to John Fields. He said he was tired of the bickering
on
the electronics newsgroups, and quit using them. He knows his website
is down, and said he hasn't got around to redoing it.

I know the feeling. But there are groups without so much of the crap.
This is one of the worst.

Oh, heavens Rick -- you need to become an amateur machinist and subscribe
to rec.crafts.metalworking.

Then you'll see how civil and on-topic this group really is!

I think you are proving my point...

--

Rick

 

[DecadentLinuxUserNumeroUn]

On Thu, 06 Nov 2014 13:44:47 -0500, rickman <gnuarm@gmail.com> Gave us:

On 11/6/2014 1:36 PM, Michael A. Terrell wrote:

I just spoke to John Fields. He said he was tired of the bickering on
the electronics newsgroups, and quit using them. He knows his website is
down, and said he hasn't got around to redoing it.

I know the feeling. But there are groups without so much of the crap.
This is one of the worst.

Yeah... all of YOUR "assessment posts" and pussy crybaby posts are a
major part of the noise level. Might as well throw in some filter file
edit session announcement posts to further clutter things.

Oh... yeah... you already did that too.

The Zimmerman complex abounds.

One can learn about the human condition so much by watching a modern TV
show, like "The Walking Dead".

John Lennon said it best though.

"A working class hero is something to be."

I'll let you figure out what the next line is, and what it means about
you.

 

[DecadentLinuxUserNumeroUn]

On Thu, 06 Nov 2014 12:49:46 -0600, Tim Wescott
<seemywebsite@myfooter.really> Gave us:

On Thu, 06 Nov 2014 13:44:47 -0500, rickman wrote:

On 11/6/2014 1:36 PM, Michael A. Terrell wrote:

I just spoke to John Fields. He said he was tired of the bickering
on
the electronics newsgroups, and quit using them. He knows his website
is down, and said he hasn't got around to redoing it.

I know the feeling. But there are groups without so much of the crap.
This is one of the worst.

Oh, heavens Rick -- you need to become an amateur machinist and subscribe
to rec.crafts.metalworking.

Then you'll see how civil and on-topic this group really is!

So, then they all use "FORD tools" "over there", eh?

Heheheh... BRL! BRL!!

Ford lovers are so dumb!

 

[amdx]

On 11/6/2014 12:49 PM, Tim Wescott wrote:

On Thu, 06 Nov 2014 13:44:47 -0500, rickman wrote:

On 11/6/2014 1:36 PM, Michael A. Terrell wrote:

I just spoke to John Fields. He said he was tired of the bickering
on
the electronics newsgroups, and quit using them. He knows his website
is down, and said he hasn't got around to redoing it.

I know the feeling. But there are groups without so much of the crap.
This is one of the worst.

Oh, heavens Rick -- you need to become an amateur machinist and subscribe
to rec.crafts.metalworking.

Then you'll see how civil and on-topic this group really is!

Yes, but rec.boats is even less on topic and more on uncivil.

oh, and I plead guilty. (not about the uncivil part)

Mikek

 

[amdx]

On 11/6/2014 2:24 PM, amdx wrote:

On 11/6/2014 12:49 PM, Tim Wescott wrote:
On Thu, 06 Nov 2014 13:44:47 -0500, rickman wrote:

On 11/6/2014 1:36 PM, Michael A. Terrell wrote:

I just spoke to John Fields. He said he was tired of the bickering
on
the electronics newsgroups, and quit using them. He knows his website
is down, and said he hasn't got around to redoing it.

I know the feeling. But there are groups without so much of the crap.
This is one of the worst.

Oh, heavens Rick -- you need to become an amateur machinist and subscribe
to rec.crafts.metalworking.

Then you'll see how civil and on-topic this group really is!


Yes, but rec.boats is even less on topic and more on uncivil.

oh, and I plead guilty. (not about the uncivil part)

Mikek

I should have added, in rec.boats the OP will warn you if
his post is boating related. lol
Mikek

 

[DecadentLinuxUserNumeroUn]

On Thu, 6 Nov 2014 12:56:40 -0800 (PST), Bill Sloman
<bill.sloman@gmail.com> Gave us:

On Friday, 7 November 2014 06:52:10 UTC+11, DecadentLinuxUserNumeroUno wrote:
On Thu, 06 Nov 2014 13:44:47 -0500, rickman <gnuarm@gmail.com> Gave us:

On 11/6/2014 1:36 PM, Michael A. Terrell wrote:

I just spoke to John Fields. He said he was tired of the bickering on
the electronics newsgroups, and quit using them. He knows his website is
down, and said he hasn't got around to redoing it.

I know the feeling. But there are groups without so much of the crap.
This is one of the worst.

snip

The Zimmerman complex abounds.

Or would, if it existed.

One can learn about the human condition so much by watching a modern TV
show, like "The Walking Dead".

Probably not.

John Lennon said it best though.

"A working class hero is something to be."

I'll let you figure out what the next line is, and what it means about
you.

http://www.metrolyrics.com/working-class-hero-lyrics-john-lennon.html

Since the quoted line is the refrain, and is thus followed by a variety of different lines, DecadentLinuxUserNumeroUno is being as off-the-wall as ever.

It is more than a little obvious which line I was referring to, Usenet
peasant.