Outdoor sensor node (Relatively low cost)

[davinci]

I have not yet seen any "template" for creating a moteino driven outdoor sensor node that is waterproof, powered by battery and features solar charging. (I know there has been discussions on the need of solar charging on other topics on this forum).

Would be interesting to just start an open discussion about this, and look at "Seeeduino Stalker - Waterproof Solar Kit" (Found here:  http://www.seeedstudio.com/depot/Seeeduino-Stalker-Waterproof-Solar-Kit-p-911.html ) as a good example of this kind of a setup and share links and experiences with alternative materials for this approach.

Personally I've been planning to create some outdoor nodes monitoring temperature, humidity and barometric pressure as a start.

For indoor sensor nodes i find the waterproof casing i linked to, too big and bulky. A smaller white casing with a separate battery room for quick replacement of batteries would be nice. Any tips here would be appreciated.

Already bought some of the waterproof enclosures that I later noticed that the seeduino stalker kit use.

Title	Comment	URL	Cost
Moteino R4	Select the one you prefer	https://lowpowerlab.com/shop/index.php?_route_=moteino-r4	$20
Waterproof enclosure	Clear plastic cover for solar panel compatability	http://www.ebay.com/itm/281392320490	$2.69
Solar panel	55x70mm. Have not found this on ebay at this size. Perhaps someone else is able to find it, or a similar?	http://www.seeedstudio.com/depot/05w-solar-panel-55x70-p-632.html	$1.95
Li-po battery	1000mah 3.7v. One with lower capacity battery could be used to lower the cost for this task?	http://www.ebay.com/itm/181601591660	$8.90
Solar Lipo Charger (3.7V)	No idea if this board is compatible with the other parts. Any experiences?	http://www.ebay.com/itm/151331887062	$5.50

Cost of material per node would be roughly 40$ with this setup. I find that a fair price. You will ofcourse need to add some sensors that bumps up the materials cost depending on your requirements.

Any thoughts / feedback would be nice.

08.12.14 Update: I bought a couple of each of the components on the list i was missing. (Battery, lipo charger and solar panel)
Will update this post when i get a simple node up and running (probably with a temp sensor).

[ColinR]

I prefer an American-made, IP-rated enclosure, with mounting flanges: http://www.polycase.com/wc-20f

A 600-650mAh LiPo would make up the difference in price above.

Interested to see how the solar charging works out for you.

C

[davinci]

Thanks for the link.

The enclosures from polycase looks better and seems to be of a higher quality than the one I linked to.

Yeah, the battery is probably a bit overkill. I will look into replacing it with a smaller one, perhaps I can downscale the solar panel too.

[ColinR]

One issue I had with larger batteries is that they are, well, bigger. A 600mAh seems to fit perfectly in my remote node cases, still allowing a screw to reach the PCB boss.

[davinci]

What size are the 600mah batteries you use?

I found one on ebay with these dimensions:

Size:
5 mm(H) *30 mm(W)* 40 mm(L)
0.19 inch (H) *1.18 inch(W)* 1.57 inch(L)

[ColinR]

These fit:

http://www.ebay.com/itm/USA-SYMA-X5C-Quadcopter-Upgrade-600mAh-3-7V-20C-Li-PO-Batteries-Battery-Spare-X5-/321532127307?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2047675.l2557&nma=true&si=N4wCnqyJ1lf47Q%252B5uCMaHe%252FGrmw%253D&orig_cvip=true&rt=nc

The pdf on that case has interior dimensions that you can use to see if it should fit.

C

[kobuki]

Be aware that most small sized batteries for RC modeling, quads, etc. don't have the PCM built-in so you can damage them by over-discharge. You can ask the seller though.

[davinci]

Thanks for the heads up Kobuku! I've been aware of this for the batteries.

There is definitely one big challenge that probably makes the lipo batteries useless for my use.
I should have known that they are not tolerant of charging at temperatures below 0 degrees celcius, and here in Norway (Europe) it's normally below 0 degrees for a few months. It's alot milder climate here in the west, but up north lipo batteries are probably useless.

Do we have any known charger boards for lead acid or nicd batteries,  to get a small-factor charger board and small-sized batteries to charge with a solar panel as we quite easily do with lipos?
Been searching around different sites and reading some blog posts, and it gets complicated..

[kobuki]

An interesting (sub)project would be to replicate what some companies do, such as in Davis weather stations. Its outdoor sensor suite uses a non-rechargable CR123 lithium battery and a 2.5F supercap. The supercap is charged in daylight using a small solar panel and discharged in the night or when the sunlight is inadequate to charge it and power the electronics. The CR123 is only used as a backup power source when recharging the supercap is not possible and/or there's no sunlight hitting solar panel either. The battery in these stations usually lasts for several years and the supercap is charging below 0 °C without problems.

[davinci]

Very interesting approach. I'm afraid designing such a solution is ahead of my skills within electronics (I'm a C#/Java programmer)

If someone came up with a project/solution on how to do it, I would be keen on trying it out on my future outdoor sensors.

But that would be a big jump towards a nice design for running outdoor sensor nodes with Moteino.

A little inspirational video: https://www.youtube.com/watch?v=xbjpQmjwMyU

[kobuki]

Well, you can just use primary batteries with the same chemistry as the CR123 (Lithium Manganese Dioxide, usually just Lithium), they're common in the standard sizes. If you can afford space for 3 AA cells, you have like 9 Ah and that should last plenty without a solar cell, even. They're good from -40 °C or so, without capacity loss.

[davinci]

Yeah. I can try 3x aa batteries to start with, and see how long the node will run, it might be just a ok solution to get started and add these solar chargering features later.
Sleeping and not submitting too frequently will help.

[TomWS]

Well, you can just use primary batteries with the same chemistry as the CR123 (Lithium Manganese Dioxide, usually just Lithium), they're common in the standard sizes. If you can afford space for 3 AA cells, you have like 9 Ah and that should last plenty without a solar cell, even. They're good from -40 °C or so, without capacity loss.

One correction, AA batteries are 3300 mAh, 3.3Ah, but 3 of them in series doesn't give you 3X the Ah, it gives you 3X the voltage, including some extra as margin above the 3.3V to operate.   You have more Wattage available, but not longer battery life at given current drain.

Lithium AA cells will supply power reliably at below freezing temperatures, alkaline will not.  (This was probably assumed, but wasn't explicitly mentioned anywhere). 

Good luck with your project!

Tom

[kobuki]

Reading the datasheet of a well known brand and emploiyng a 10% safety margin on the textbook value, I'd rather say it's 3 Ah than 3.3 Ah. It's debatable though. What is your real life experience with them?

OTOH, I admit that multiplying the Ah capacity by the number of batteries is a little over-simplifying things, but as you pointed out, it provides 3x the energy so the Wh increases approx. 3-fold. It means around 1/3 of the amperage thus 3x longer service time, in general. The end result is the same from this standpoint, and that's what is important.

I explicitly mentioned the usability below freezing temperatures in the post you answered to. Please also see the DS I linked above.

[davinci]

Am I correct?

One AA battery at 1.3v x 3 in series would provide 3.9~.3.7v as a end result?

[kobuki]

The Lithium batteries we're discussing are 1.5V. You can directly power a moteino using 3 of them in series, or employ tricks to be able to use 2  cells at 3V or use a boost converter. I think the simplest would be 3xAA or 3xAAA, depending on the available room in your project box. That would provide 4.5V nominally.

[TomWS]

Reading the datasheet of a well known brand and emploiyng a 10% safety margin on the textbook value, I'd rather say it's 3 Ah than 3.3 Ah. It's debatable though. What is your real life experience with them?

My real life experience is running PIC-based remote wireless soil moisture sensors in a harsh Texas environment (extreme hot and cold) for several years and getting up to 4 years of operation without a battery change.  As you say, it's hard to tell the difference between +/-10% when the average drain is so microscopically small.

OTOH, I admit that multiplying the Ah capacity by the number of batteries is a little over-simplifying things,

uh, with all due respect, I wouldn't say that is 'over-simplifying', it is incorrect.  Wh is multiplied, yes, Ah is not.  My comment wasn't intended as a dig and I'm sure you understand the relationship, but I just wanted to make sure those who are learning to learn the correct things.

I explicitly mentioned the usability below freezing temperatures in the post you answered to. Please also see the DS I linked above.

Yes, I missed the 'with the same chemistry' reference.  Sorry.

Tom

[kobuki]

What is the average power draw on your PIC nodes? Have you ever measured it or tried to estimate?

OK, then I'd like to add for completeness that Ah isn't multiplied is not entirely correct either. It's not multiplied in a series topology. It is in a parallel one. I don't know if it's recommended though, for these batteries. But it wouldn't be very useful for davinci's (cool name btw) project, I think.

[TomWS]

What is the average power draw on your PIC nodes? Have you ever measured it or tried to estimate?

I did calculate it, measure it, and prove (through battery life) that the calculations were 'close enough'.  Precise calculations, as in this case, weren't feasible because it was DEFINITELY not a controlled environment 

I designed those over 8 years ago so, sorry, I don't remember the specifications.

BTW, I was using Linx Technology radios in that system.  They worked pretty well, but I had to code the comms protocol myself and I'm glad that I don't have to do THAT again!

Later...

[ColinR]

OTOH, I admit that multiplying the Ah capacity by the number of batteries is a little over-simplifying things, but as you pointed out, it provides 3x the energy so the Wh increases approx. 3-fold. It means around 1/3 of the amperage thus 3x longer service time, in general. The end result is the same from this standpoint, and that's what is important.

With three batteries, you either get three times the lifetime at the same voltage of one battery by putting them in parallel, or three times the voltage by putting them in series.

You can think of three 1.5V AA batteries in series as a 4.5V battery with the combined energy of the three. If you had a fixed power load, you would indeed have three times the capacity, at 1/3 the current, giving you 3x lifetime. If you had a fixed current load, your rate of power discharge would be 3x, and your lifetime would be the same as a single cell. If you have a fixed impedance load (like a resistor), you'd get three times the discharge current at three times the voltage, and your lifetime would actually be cut by 3x.

For something like a linear regulator, the power required for the load is the same, but you lose everything above the required voltage, meaning higher voltage actually reduces the effective capacity you have available. A 600mAh 3.7V LiPo is roughly as effective at powering a 3.3V device through a linear regulator as 600*9/3.7= 1459mAh at 9V.

C

[TomWS]

<...snip>

You can think of three 1.5V AA batteries in series as a 4.5V battery with the combined energy of the three. If you had a fixed power load, you would indeed have three times the capacity, at 1/3 the current, giving you 3x lifetime. If you had a fixed current load, your rate of power discharge would be 3x, and your lifetime would be the same as a single cell. If you have a fixed impedance load (like a resistor), you'd get three times the discharge current at three times the voltage, and your lifetime would actually be cut by 3x.

Correct, so far... although I'd never put batteries in parallel, especially LiPo!

For something like a linear regulator, the power required for the load is the same, but you lose everything above the required voltage, meaning higher voltage actually reduces the effective capacity you have available. A 600mAh 3.7V LiPo is roughly as effective at powering a 3.3V device through a linear regulator as 600*9/3.7= 1459mAh at 9V.

C

uh... not quite.  The current load (not the power load), at the power source, is the same in both cases (3.7V LiPo or 9V alkaline) so a 600mAh battery in either case would last the same time.  Your own example demonstrated that, 3 batteries would last the same as a single cell with the same current load.

It's true, with the 9V alkaline, you would be throwing away a lot of wattage in the form of heat across the linear regulator (roughly 9/3.7 X) but we're talking about mAh rating of the battery.  A 600mAh 9V battery COULD deliver more power, if it wasn't thrown away in the regulator.  If it was a switching regulator, then the current load would be dramatically reduced in the 9V power source and a 600mAh 9V battery would last a lot longer (9/3.3) vs (3.7/3.3) if the efficiency of the switching regulator was the same for both voltages (not entirely realistic, but good enough for the example).

Tom

[kobuki]

@ColinR

OK, but we're talking about Moteinos, not theoretical loads. We can assume the Moteinos are in the "fixed power load" category.

The LDOs are a different matter, now we're just looking at the devices as black boxes consuming power. But as I've also mentioned in this thread too, it's possible to remove the LDO from the Moteino and use AA cells directly and thus increasing power efficiency. There's a thread about it with recent posts too.

The rest is more adequately answered by TomWS than I would have written.

[ColinR]

<...snip>

You can think of three 1.5V AA batteries in series as a 4.5V battery with the combined energy of the three. If you had a fixed power load, you would indeed have three times the capacity, at 1/3 the current, giving you 3x lifetime. If you had a fixed current load, your rate of power discharge would be 3x, and your lifetime would be the same as a single cell. If you have a fixed impedance load (like a resistor), you'd get three times the discharge current at three times the voltage, and your lifetime would actually be cut by 3x.

Correct, so far... although I'd never put batteries in parallel, especially LiPo!

For something like a linear regulator, the power required for the load is the same, but you lose everything above the required voltage, meaning higher voltage actually reduces the effective capacity you have available. A 600mAh 3.7V LiPo is roughly as effective at powering a 3.3V device through a linear regulator as 600*9/3.7= 1459mAh at 9V.

C

uh... not quite.  The current load (not the power load), at the power source, is the same in both cases (3.7V LiPo or 9V alkaline) so a 600mAh battery in either case would last the same time.  Your own example demonstrated that, 3 batteries would last the same as a single cell with the same current load.

It's true, with the 9V alkaline, you would be throwing away a lot of wattage in the form of heat across the linear regulator (roughly 9/3.7 X) but we're talking about mAh rating of the battery.  A 600mAh 9V battery COULD deliver more power, if it wasn't thrown away in the regulator.  If it was a switching regulator, then the current load would be dramatically reduced in the 9V power source and a 600mAh 9V battery would last a lot longer (9/3.3) vs (3.7/3.3) if the efficiency of the switching regulator was the same for both voltages (not entirely realistic, but good enough for the example).

Tom

Yes, tis true. They hide the potential energy of the battery by reporting it in units that divide it out. The 600mAh LiPo has energy roughly proportional to 3.7 * 600mAh, while the 9V is 550mAh * 9V, so it's just how much you're throwing away that comes out as the ratio of voltages.

C

[TomWS]

<...snip>
Yes, tis true. They hide the potential energy of the battery by reporting it in units that divide it out. The 600mAh LiPo has energy roughly proportional to 3.7 * 600mAh, while the 9V is 550mAh * 9V, so it's just how much you're throwing away that comes out as the ratio of voltages.

C

To my mind, mAh rating is the most useful parameter there is.  If you know the average current load, you know how long any battery will last given its mAh rating.  I have a spreadsheet that, given the load model, tells me how many hours (or years, as the case may be) any of most commercially available batteries will last.

Tom

[ColinR]

It really depends on what you're powering. Wh is plenty useful for comparison across power sources.

[ColinR]

@ColinR

OK, but we're talking about Moteinos, not theoretical loads. We can assume the Moteinos are in the "fixed power load" category.

With the LDO, the Moteino will take 3.3V * whatever current it needs. The power consumed is input voltage * whatever that current happens to be. To be most efficient, you want just enough voltage to satisfy the LDO regulator.

I'll eat the efficiency loss of that tiny LDO for the peace of mind and stability it offers.

C

[kobuki]

Well, yeah, you're right. And with all the battery-powered low power devices that's why the mAh rating is probably the most useful one. And LDOs are very cheap and simple components compared to small switching regulators.

[davinci]

Found these Lithium-Ion batteries interesting: http://www.tadiranbat.com/index.php/tli-series-rechargeable

Datasheet: http://www.tadiranbat.com/pdf/TLI-1550A.pdf

Perhaps they could be charged with existing standard li-po solar charger boards?

Does not look like many stores are stocking them.. Any experiences with this specific battery or similar products?

[TomWS]

I think the only thing I like about this battery is the voltage.  4.1V is perfect for 3.3V LDOs.  However, the battery voltage drops almost immediately and pretty linearly to about 2.7V and then falls off a cliff.  The worst of it is how it collapses pretty quickly at cold temperatures and, if you were using the RFM69HW, it wouldn't take too many transmits to get the voltage down below the LDO dropout voltage. 

I doubt that LiPo chargers would work with this battery, although I did NOT research that.  It's just that the charging protocol is different than LiPo.  The protocol is simple, but dependent on temperature and, IIRC, rate of discharge usage.

I'm also not impressed with the mAh rating. 

They make a grand claim about battery life, but then advise that voltage falls off much faster after about 3000 charge cycles.  At the rate this thing discharges, you'd have to charge it every day or more.

Net: These are my 'impressions', I did not do a thorough analysis and do not plan to, given these impressions.

Tom

[davinci]

Tom, when you mention that the voltage drops more quickly after the 3000 charge cycles, would you calculate with one charge cycle a day for a Moteino running a sensor or two, transmitting once a minute?

If it is so, the voltage drops are first after 8 years of usage... (365/3000 = 8,21)

[TomWS]

What I was trying to say was that the battery dropoff is bad enough when the battery is fresh, but after 3000 charge cycles, the voltage drop off rate is significantly worse.  Further, the fact that the voltage would drop below your 3.3V limit after just a few transmits (even with a fresh battery) at very cold temperatures, means that you will need to charge much more frequently than once a day, hence, battery life won't be anywhere close to the 8 year life you're calculating.

One thing I don't know is which radio you're using?  Is it the RFM69W or the RFM69HW?

Tom

[davinci]

Allright. Sure, I would never believe a battery would last for 8 years..

I'm using the RFM69W on my nodes and RFM69WH on the gateway, flashing a SD Card with raspbian wheezy right now. Have not yet decided what solution to run on the RPi.

The system Felix built is quite interesting with NodeJS. But I also think OpenHAB is a good alternative with its modular/plugin based architecture and support for many home automation systems.

[ColinR]

I think the real answer is what you want to write code in, and how much tinkering you want to do.

I use python server-side and keep javascript on the client side, and have a handler for moteinos specifically that squirts data into databases for display. Works with stock code I've written for remote nodes as well.

The serial handler on the gateway is here:
https://github.com/iinnovations/iicontrollibs/blob/master/mote/serialhandler.py

The mote and gateway sketches are on there as well, but I have made a few edits since. The nice part is that if you have the handler running on the pi, when you connect a mote node and enable reporting, the io just magically appear as inputs on the Pi web interface and you may use them in channels.

I just set up a laboratory monitoring system for a buddy that I'll post about shortly that demonstrates, but this gives you a basic idea of how it works:
http://www.cupidcontrols.com/2014/08/adventures-in-moteino-remote-temperature-monitor/

Cheers,
C

[kiwisincebirth]

Just though I would I would share my (short) experience with battery powered Moteino.

I use 3 x AA Eneloop cells powering a remote temperature (DS18B20) sensor. The code sleeps puts the moteino to sleep as much as possible, but wakes up the radio to relay temperature value every minute, and battery voltage every 10 minutes, so 66 messages per hour in total. Every message is exactly 4 bytes. The battery voltage is monitored via 2 x 1 meg ohm series resistors (voltage divider), so there is a few micro Amps constant battery drain. I am located in Sydney, temperature ranges between 10 and 30 degrees C, as measured by the sensor itself.

See attached battery voltage profile.

[TomWS]

Thanks for telling us about your project.  I just wanted to let you know that there is a way to measure the voltage at the Moteino (won't be battery voltage if you're using the LDO) that doesn't require an external divider or added current.  Basically you read the internal voltage reference and calculate the analog reference voltage from the resulting ratio (because the internal reference is very accurate).

Here's some code that does it:

Code: [Select]

/******************************************************************************
*
*		readVcc()
*
******************************************************************************/
unsigned int readVcc() {
  unsigned int result;
  byte saveADMUX;
  
  saveADMUX = ADMUX;
  
  // Read 1.1V reference against AVcc
  ADMUX = _BV(REFS0) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1);
  delay(2); // Wait for Vref to settle
  ADCSRA |= _BV(ADSC); // Convert
  while (bit_is_set(ADCSRA,ADSC));
  result = ADCL;
  result |= ADCH<<8;
  result = 1126400L / result; // Back-calculate AVcc in mV
  
  ADMUX = saveADMUX;  // restore it on exit...
  return result;
}

Cheers!

[kobuki]

I'd like to add that on an unmodified Moteino this is not very useful as you also pointed out since it powers the chip via the 3.3V LDO. OTOH, the internal referenec sadly has some variance on the 328p, from ~1.0 .. ~1.2 V, so it should be calibrated before use. More info here.

[TomWS]

I'd like to add that on an unmodified Moteino this is not very useful as you also pointed out since it powers the chip via the 3.3V LDO. OTOH, the internal referenec sadly has some variance on the 328p, from ~1.0 .. ~1.2 V, so it should be calibrated before use. More info here.

Well I know that the specification table says 1.0-1.2V, but you look at any of the curves in the detailed part of the data sheet you will see that the range is more like 1.126-1.137 over voltage and temperature range, which makes sense since it is a bandgap source.  And it's also good enough for me to monitor battery degradation   

Tom

[Felix]

Just though I would I would share my (short) experience with battery powered Moteino.
I use 3 x AA Eneloop cells powering a remote temperature (DS18B20) sensor. The code sleeps puts the moteino to sleep as much as possible, but wakes up the radio to relay temperature value every minute, and battery voltage every 10 minutes, so 66 messages per hour in total. Every message is exactly 4 bytes. The battery voltage is monitored via 2 x 1 meg ohm series resistors (voltage divider), so there is a few micro Amps constant battery drain. I am located in Sydney, temperature ranges between 10 and 30 degrees C, as measured by the sensor itself.
See attached battery voltage profile.

Wow pretty nice performance, thanks for sharing, still going strong at 3.65v, would be nice to hear back again about the performance, how long before it dies.