High Pass DSP?

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I'm not sure if it's not here already, but I'm often using "aproximated" moving average - I substract averaged value from sum variable and add a new value. That means you don't have to keep track of all the previous values.

Computers don't make errors - What they do they do on purpose.

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>Also interesting what you would do for a sensor that is a hundred feet up in a tree, especially where there are varmints around (especially monkeys).

 

I have ideas, not solutions :)

 

One would think some industry has this problem solved- telephone/power companies, zoos/elementary schools, etc.

 

 

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ka7ehk wrote:
It finally failed in late June.
That's where the analysis comes in for worst case scenario.  Obviously a larger (or higher efficiency) PV would be needed, but how much larger?  A larger battery might suffice.  Or a combination of these.

 

For your test case, did you use an MPPT charger?

 

Also, remember that the sensor will lack the uSD card and the associated power draw.  If you put the trigger smarts into the sensor node's firmware, then you can keep the radio power draw down to a minimum.  Sending 'raw' data over the wireless link rather than formatted uSD file records will likewise reduce air time and power.

 

A variety of low-power radio options exist, even for always-on receivers.  However, you could schedule the link.  Say, Listen for 1 second every 10 seconds.  This immediately cuts radio power by a factor of 10. The sensor could likewise keep track of time, and check in during the listen window.  Packet exchange could also resynchronise clocks on the base with the node to avoid drift.  Worst case is the node would accumulate 9 seconds of data from a trigger that just misses the last exchange.  Nine seconds, 10 sample per second, 3 axis per sample, 32-bits per axis = about 1KB.  No worries for an mcu with 2KB SRAM.

 

 

"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

"Wisdom is always wont to arrive late, and to be a little approximate on first possession."

"When you hear hoofbeats, think horses, not unicorns."

"Fast.  Cheap.  Good.  Pick two."

"We see a lot of arses on handlebars around here." - [J Ekdahl]

 

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Rather than wireless, can you simply used a wired connection from he near ground base & sensor up in the tree?   Of course, then you need 2 cases, weathertight connectors, cable, etc & anything near ground level is subject to theft & tampering---so that could be the biggest drawback.

 

As far as solar--maybe there is a way to mount cells at the very top of the tree (like a selfie stick), so that they are always exposed.   Or perhaps this is a foolish idea, since those limbs would be the weakest, or hard to deal with (too tall).

 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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avrcandies wrote:

can you simply used a wired connection

 

 

ka7ehk wrote:

Also interesting what you would do for a sensor that is a hundred feet up in a tree, especially where there are varmints around (especially monkeys).

"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

"Wisdom is always wont to arrive late, and to be a little approximate on first possession."

"When you hear hoofbeats, think horses, not unicorns."

"Fast.  Cheap.  Good.  Pick two."

"We see a lot of arses on handlebars around here." - [J Ekdahl]

 

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curtvm - pretty sure there are solutions. Its a matter of finding them.

 

joeymorin - the problem was insufficient sizing of the solar cell. Unfortunately, I had no usable data to base any design on. The Boulder test was sort of a best-worst-case scenario. Winter, there is lots of sun. But, elsewhere, its a big problem and especially in realms north of, lets say, 40N, or south of 40S. It would have been a VERY rapid failure at my own house. In a northern hardwood forest, it would have been unworkable, summer or winter; just too much shade and too little sun whole year. That is part of why I've been looking at external power delivery that accommodates more than just solar.

 

avrcandies - wired would probably be the simplest technically and maybe logistically. Simply not having to climb a tree after installation would be a big plus; many kinds of trees are really hard to climb. The unknown is how well a wire link would stand up. In some places, squirrels are a big problem with scientific gear, especially wires (they chew wires). In other places, its bears, or monkeys or other critters. Basically, there is no free lunch! The "something like a selfie stick" is not a bad idea, but something like that that sticks up high is an ideal perch for many kinds of birds and bird poop is a real killer for photo cells (in addition to just covering them up).

 

Some great thoughts and ideas here. It is great to have some of these seemingly "off the wall" suggestions. They really can lead to some useful rethinking, some times.

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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ka7ehk wrote:
something like that that sticks up high is an ideal perch for many kinds of birds and bird poop is a real killer for photo cells (in addition to just covering them up).
These should have a minimal impact on PV effectiveness.

 

Although a PV panel on the end of a 'selfie stick' would bring issues of durability, esp w.r.t wind, likely worse in winter.

 

Pity milliwatt-scale RTGs aren't widely available...

https://www.google.com/search?q=milliwat+rtg

;-)

"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

"Wisdom is always wont to arrive late, and to be a little approximate on first possession."

"When you hear hoofbeats, think horses, not unicorns."

"Fast.  Cheap.  Good.  Pick two."

"We see a lot of arses on handlebars around here." - [J Ekdahl]

 

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"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

"Wisdom is always wont to arrive late, and to be a little approximate on first possession."

"When you hear hoofbeats, think horses, not unicorns."

"Fast.  Cheap.  Good.  Pick two."

"We see a lot of arses on handlebars around here." - [J Ekdahl]

 

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ka7ehk wrote:
Unfortunately, I had no usable data to base any design on.
There's a simple rule that can be adjusted given insolation data.

ka7ehk wrote:
In a northern hardwood forest, it would have been unworkable, summer or winter; just too much shade and too little sun whole year.
One PV installation into the Crosstimbers forest (here, primary are live oaks) resulted in the intentional fell of a tree.

ka7ehk wrote:
In some places, squirrels are a big problem with scientific gear, especially wires (they chew wires).
A neighbor is successful with armored cable and sheet metal junction boxes with buried cable to the power source.

The river plain has some impressive tall (for here) trees that have a nice sway; plain also has hogs and coyotes follow the creeks away from the river.

Data for a local study of bobcats was gathered by trail cameras one of which was stolen (not "stolen" by fauna)

 


Simplify Small Solar Systems* with Hysteretic Controller | Analog Devices

...

It is important to correctly size the battery and the solar panel for a specific application. As a general rule, [it's simple] ...

...

These relationships were derived for Milpitas, California to give 4 days’ run time on unassisted battery power, with the panel oriented for maximum winter insolation.

...

Solar Insolation on Earth Dataset | Science On a Sphere (USA NOAA)

There's mean annual insolation plotted on CONUS but I couldn't recall that URL.

 

edit : typo

 

"Dare to be naïve." - Buckminster Fuller

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gchapman wrote:

One PV installation into the Crosstimbers forest (here, primary are live oaks) resulted in the intentional fell of a tree.

How?

"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

"Wisdom is always wont to arrive late, and to be a little approximate on first possession."

"When you hear hoofbeats, think horses, not unicorns."

"Fast.  Cheap.  Good.  Pick two."

"We see a lot of arses on handlebars around here." - [J Ekdahl]

 

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Problems is that there are places, here in the Coastal NW US, for example, where winter overcast can extend to intervals of several weeks. I would expect as bad in the boreal forest zone. There are places in Oregon and Washington coastal mountains with 200" + rain per year; that rain does not happens when the sun is shining! Similar in coastal British Columbia, Canada.

 

Obviously, there are places where any kind of instrument with any kind of power is challenged!

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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One week, the tree was there; next week, she/he wasn't.

Rush - The Trees Lyrics | AZLyrics.com

...

By hatchet, axe and saw

 

"Dare to be naïve." - Buckminster Fuller

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:-)

 

gchapman wrote:
By hatchet, axe and saw
Someone who hates solar and wanted it gone?  Or someone who loves solar and wanted it for themselves...?

 

"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

"Wisdom is always wont to arrive late, and to be a little approximate on first possession."

"When you hear hoofbeats, think horses, not unicorns."

"Fast.  Cheap.  Good.  Pick two."

"We see a lot of arses on handlebars around here." - [J Ekdahl]

 

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joeymorin wrote:
Or someone who loves solar and wanted it for themselves...?
Love of money (USD/KWh, incentives) versus love of tree ... PV "won".

 

"Dare to be naïve." - Buckminster Fuller

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Pity milliwatt-scale RTGs aren't widely available...

I had the same thought and was about to post the following , when I saw JoeyM had mentioned RTG

 

if it's good enough for pacemeakers, why not for trees?

https://www.orau.org/ptp/collection/Miscellaneous/pacemaker.htm

At present (2003), there are between 50 and 100 people in the US who have nuclear powered pacemakers.

When one of these  individuals dies, the pacemaker is supposed to be removed and shipped to Los Alamos where the plutonium will be recovered.

 

https://uk.reuters.com/article/health-heart-pacemaker-dc/nuclear-pacemaker-still-energized-after-34-years-idUKN1960427320071219

Parsonnet said 139 people received the first versions of the nuclear pacemaker and even after 88 years, when half the plutonium would have decayed, the batteries would have enough power to drive the circuit.

 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

Last Edited: Thu. Jul 11, 2019 - 12:47 AM
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Jim,

 

I believe i have a simple, efficient solution.   It uses a low pass filter to generate biases for each of the three channels, then proceeds to use magnitude based on square-sum of the measurements with bias removed.

 

Problem: Given a sequence of biased accel measurements from three channels x, y and z, find a way to remove slowly varying bias and estimate acceleration magnitude for swaying trees.

Solution:

part 1) Define xb, yb, zb, to be the bias estimate for x, y and z, respectively.   After each measurement, update the bias estimate via the low pass filter

xb = xb - (xb >> n) + (x >> n); yb = yb - (yb >> n) + (y >> n); zb = xb - (xb >> n) + (z >> n);

Given that xb will vary with temperature (time constant on the order of an hour, say, I'd set n to 10-12 (i.e., time constant of 2^10-2^12).

part 2) Define xu, yu, zu to be the unbiased estimate for each measurement

xu = x - xb; yu = y - yb; zu = z - zu;

part 3) Generate a magnitude estimate.  I provided an efficient assember program in another thread by OP.

part 4) average output from part 3 as needed

 

Edit: you will probably want to seed the bias xb, yb, zb.  You could use the first measurement or use from calibration data.

Last Edited: Sat. Jul 20, 2019 - 07:17 PM
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Hi Matt -

 

That basic technique is one that I looked at in detail, earlier. Transfer-function wise, it is exactly equivalent to high-pass though the time constants used, need to be slightly different for same frequency response (not an issue). I did have problems, however, numerically. The subtracted low-pass never turned out as good at eliminating biases as the high pass. I have no clue why. 

 

I really do appreciate the effort that you have taken. I will look at your algorithm in more detail, though I am off for a week long backpack trip near Mt. St. Helens (the one that blew up in 1980). Will respond in more detail when I have been able to look at it.

 

Again, many thanks

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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