Cheap Oscilloscope measurement of small current?
Hello, all. I'm working (very slowly, but working) on some designs that
will be battery (and possibly solar) powered sensors with a wireless
data backhaul (likely 433 or 915MHz).
As part of my never ending quest for more tools, I'm starting to educate
myself on what I may need to get measurements on current usage over time
for these devices. I want to be able to quantify power usage while it is
asleep, sensing, sending data, etc..."does changing this code shorten
the radio on time?"
I'm sure Agilent would be happy to sell me a fancy oscilloscope current
probe for more than my condo cost, but I'm looking for something more
cost effective.
Suggestions from the hive mind?
Thanks.
-Pete
A current sampling resistor, low offset amplifier (like an IC
Instrumentation amp, and an A/D to a PC with a simple data acquisition SW.
The SW often comes w/ the A/D or is freeware.
You could also use a commercial Hall Effect current sensor.
Once you have the data, a simple addition program or Excel will integrate
up the A-H.
FWIW,
-John
=============
Hello, all. I'm working (very slowly, but working) on some designs that
will be battery (and possibly solar) powered sensors with a wireless
data backhaul (likely 433 or 915MHz).
As part of my never ending quest for more tools, I'm starting to educate
myself on what I may need to get measurements on current usage over time
for these devices. I want to be able to quantify power usage while it is
asleep, sensing, sending data, etc..."does changing this code shorten
the radio on time?"
I'm sure Agilent would be happy to sell me a fancy oscilloscope current
probe for more than my condo cost, but I'm looking for something more
cost effective.
Suggestions from the hive mind?
Thanks.
-Pete
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To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
and follow the instructions there.
Hello, all. I'm working (very slowly, but working) on some designs that
will be battery (and possibly solar) powered sensors with a wireless
data backhaul (likely 433 or 915MHz).
As part of my never ending quest for more tools, I'm starting to educate
myself on what I may need to get measurements on current usage over time
for these devices. I want to be able to quantify power usage while it is
asleep, sensing, sending data, etc..."does changing this code shorten
the radio on time?"
I'm sure Agilent would be happy to sell me a fancy oscilloscope current
probe for more than my condo cost, but I'm looking for something more
cost effective.
Suggestions from the hive mind?
Thanks.
-Pete
Hello Pete,
for comparative measurements you could supply the cirquit from
a (foil) capacitor which is recharged by a relative high-ohmic resistor
or current source. From the voltage dips on the capacitor you could
estimate the (integrated) energy of the wakeup-phases.
with best regards
Andreas
Hi Pete:
I ended up getting the Rigol DS1052E. It turns out that they make the
low end scopes for HP and are very high quality.
See:
http://www.prc68.com/I/RigolDS1052E.shtml
You can get a new one for under US$400 and then do a software hack to
double it's bandwidth (i.e. make it into a $1000 class scope).
Watch the video blogs linked at the above page.
Have Fun,
Brooke Clarke
http://www.PRC68.com
Peter Loron wrote:
Hello, all. I'm working (very slowly, but working) on some designs that
will be battery (and possibly solar) powered sensors with a wireless
data backhaul (likely 433 or 915MHz).
As part of my never ending quest for more tools, I'm starting to educate
myself on what I may need to get measurements on current usage over time
for these devices. I want to be able to quantify power usage while it is
asleep, sensing, sending data, etc..."does changing this code shorten
the radio on time?"
I'm sure Agilent would be happy to sell me a fancy oscilloscope current
probe for more than my condo cost, but I'm looking for something more
cost effective.
Suggestions from the hive mind?
Thanks.
-Pete
volt-nuts mailing list -- volt-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
and follow the instructions there.
I'm doing quite a bit of this and like most things, the answer is "it
depends. "
What I'm doing right now is using a resistor in series with the input
of a low leakage micropower Low DropOut (LDO) regulator because this (15
uA) circuit will run off of a regulated supply. The LDO has a steady
state consumption of a few microamps and that is largely a function of
input voltage and operating temperature at the low operating currents
I'm dealing with. My workshop temperature is constant enough. This
works well below a uA. I just use my plain old Tek scope with two
channels in differential mode. If I neede teh extra channel I'd brew a
diff amp or use something like this:
http://datasheets.maxim-ic.com/en/ds/MAX9938.pdf
I believe you have a much more complex problem. You will be operating
from battery or solar supplies that likely have a defined voltage and
internal resistance over time. This can have a profound impact on
operating time, particularly if subtle considerations are as significant
as you imply they are. You'll either need to take a lot of measurements
and model the supply carefully, or you'll need a good simulator of the
supply.
On 11/4/2010 6:07 PM, Peter Loron wrote:
Hello, all. I'm working (very slowly, but working) on some designs that
will be battery (and possibly solar) powered sensors with a wireless
data backhaul (likely 433 or 915MHz).
As part of my never ending quest for more tools, I'm starting to educate
myself on what I may need to get measurements on current usage over time
for these devices. I want to be able to quantify power usage while it is
asleep, sensing, sending data, etc..."does changing this code shorten
the radio on time?"
I'm sure Agilent would be happy to sell me a fancy oscilloscope current
probe for more than my condo cost, but I'm looking for something more
cost effective.
Suggestions from the hive mind?
Thanks.
-Pete
--
mailto:oz@ozindfw.net
Oz
POB 93167
Southlake, TX 76092 (Near DFW Airport)
Well, there's no hard goal of battery life or consumption. However once
I get things working, I do want to optimize power consumption to get
good battery life, or be able to run it from a small solar cell.
I'm thinking that for the initial work, I can simply use a regulated
bench supply as the power source.
I'll take a look at those MAX parts...might be worth checking out.
Thanks.
-Pete
On Fri, 2010-11-05 at 09:08 -0500, Oz-in-DFW wrote:
I'm doing quite a bit of this and like most things, the answer is "it
depends. "
What I'm doing right now is using a resistor in series with the input
of a low leakage micropower Low DropOut (LDO) regulator because this (15
uA) circuit will run off of a regulated supply. The LDO has a steady
state consumption of a few microamps and that is largely a function of
input voltage and operating temperature at the low operating currents
I'm dealing with. My workshop temperature is constant enough. This
works well below a uA. I just use my plain old Tek scope with two
channels in differential mode. If I neede teh extra channel I'd brew a
diff amp or use something like this:
http://datasheets.maxim-ic.com/en/ds/MAX9938.pdf
I believe you have a much more complex problem. You will be operating
from battery or solar supplies that likely have a defined voltage and
internal resistance over time. This can have a profound impact on
operating time, particularly if subtle considerations are as significant
as you imply they are. You'll either need to take a lot of measurements
and model the supply carefully, or you'll need a good simulator of the
supply.
On 11/4/2010 6:07 PM, Peter Loron wrote:
Hello, all. I'm working (very slowly, but working) on some designs that
will be battery (and possibly solar) powered sensors with a wireless
data backhaul (likely 433 or 915MHz).
As part of my never ending quest for more tools, I'm starting to educate
myself on what I may need to get measurements on current usage over time
for these devices. I want to be able to quantify power usage while it is
asleep, sensing, sending data, etc..."does changing this code shorten
the radio on time?"
I'm sure Agilent would be happy to sell me a fancy oscilloscope current
probe for more than my condo cost, but I'm looking for something more
cost effective.
Suggestions from the hive mind?
Thanks.
-Pete
If you wouldn't mind, I'd appreciate a more detailed explanation of the setup you're using. A stab in the dark gives me this schematic:
On Nov 5, 2010, at 7:08, Oz-in-DFW lists@ozindfw.net wrote:
I'm doing quite a bit of this and like most things, the answer is "it
depends. "
What I'm doing right now is using a resistor in series with the input
of a low leakage micropower Low DropOut (LDO) regulator because this (15
uA) circuit will run off of a regulated supply. The LDO has a steady
state consumption of a few microamps and that is largely a function of
input voltage and operating temperature at the low operating currents
I'm dealing with. My workshop temperature is constant enough. This
works well below a uA. I just use my plain old Tek scope with two
channels in differential mode. If I neede teh extra channel I'd brew a
diff amp or use something like this:
http://datasheets.maxim-ic.com/en/ds/MAX9938.pdf
I believe you have a much more complex problem. You will be operating
from battery or solar supplies that likely have a defined voltage and
internal resistance over time. This can have a profound impact on
operating time, particularly if subtle considerations are as significant
as you imply they are. You'll either need to take a lot of measurements
and model the supply carefully, or you'll need a good simulator of the
supply.
On 11/4/2010 6:07 PM, Peter Loron wrote:
Hello, all. I'm working (very slowly, but working) on some designs that
will be battery (and possibly solar) powered sensors with a wireless
data backhaul (likely 433 or 915MHz).
As part of my never ending quest for more tools, I'm starting to educate
myself on what I may need to get measurements on current usage over time
for these devices. I want to be able to quantify power usage while it is
asleep, sensing, sending data, etc..."does changing this code shorten
the radio on time?"
I'm sure Agilent would be happy to sell me a fancy oscilloscope current
probe for more than my condo cost, but I'm looking for something more
cost effective.
Suggestions from the hive mind?
Thanks.
-Pete
--
mailto:oz@ozindfw.net
Oz
POB 93167
Southlake, TX 76092 (Near DFW Airport)
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Try a secondhand Keithley or Stranford Current Converter
Met vriendelijke groeten
Regards
ElectronicsAndBooks@Yahoo.com
http://www.ElectronicsAndBooks.tk
TEL +31-(0)6-36024590
--- On Thu, 11/4/10, Peter Loron peterl@standingwave.org wrote:
From: Peter Loron peterl@standingwave.org
Subject: [volt-nuts] Cheap Oscilloscope measurement of small current?
To: volt-nuts@febo.com
Date: Thursday, November 4, 2010, 7:07 PM
Hello, all. I'm working (very slowly,
but working) on some designs that
will be battery (and possibly solar) powered sensors with a
wireless
data backhaul (likely 433 or 915MHz).
As part of my never ending quest for more tools, I'm
starting to educate
myself on what I may need to get measurements on current
usage over time
for these devices. I want to be able to quantify power
usage while it is
asleep, sensing, sending data, etc..."does changing this
code shorten
the radio on time?"
I'm sure Agilent would be happy to sell me a fancy
oscilloscope current
probe for more than my condo cost, but I'm looking for
something more
cost effective.
Suggestions from the hive mind?
Thanks.
-Pete
volt-nuts mailing list -- volt-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
and follow the instructions there.