I have been playing around with the new WeatherShield. It works great and I really like the proto type area on the board to add additional small circuits.
I'm trying to get the low power state under 200-300ua and having some problems. First, I noticed that the voltage divider was always on when the mote is plugged into the USB 5v supply. From some investigation I find that A3 just can't go high enough to turn off the p-FET completely with a 5.1volt supply - does this makes sense? If I run it on a 3.7v lipo, then A7 does go to zero volts ( or very close - .7mv ) and the voltage divider is off. Using 3 AAA cells, the voltage divider is still on, again since A3 can't go high enough. Since I am using a lipo battery, this seems to be working for me. Am I missing anything here that would allow the p-FET to switch off on higher Vin's?
Also, something else seems to be consuming power. Is there a low power mode for the Si7021 or the BMP180 that I should try? I am using the LowPower.powerDown library and I had about 15ua current flow just on the Mote alone without the weathershield. Any thoughts appreciated here?
thanks
Jim
Update - I had commented out the code to initialize the flash while debugging other initialization problems. Once I put that code back in, sleep current dropped to 36ua. I am happy with that.
It's 180ua sleep current if I run on 3AAA's versus the lipo at 36 ua.
Hi Jim,
As seen in the WeatherShield.ino sketch (https://github.com/LowPowerLab/WeatherShield/blob/master/WeatherShield.ino), here's how you turn ON the P-mos to read the voltage:
//*************** READING BATTERY VOLTAGE *********************
//turn MOSFET ON and read voltage, should give a valid reading
pinMode(A3, OUTPUT);
digitalWrite(A3, LOW);
Serial.print(" BATT: ");
Serial.println(analogRead(A7));
pinMode(A3, INPUT); //put A3 in HI-Z mode (to allow mosfet gate pullup to turn it OFF)
//*************** READING BATTERY VOLTAGE *********************
You have to make sure the A3 switch is HI-Z otherwise the Pmos will be closed and allow current to flow. It is a very sensitive Pmos and almost anything will turn it on (Vgs). HiZ on A3 will allow the gate to be pulled up to Vin and hence open the switch and turn off the voltage divider.
And yes there are low power modes for the sensors, although they are quite low power already in standby. For more savings please see the datasheets and the libraries.
Hi Felix,
I still can't get the voltage divider to turn off while running at 5volts vcc using the usb adapter. I am running the WeatherShield exactly as it is on github so A3 should be high Z mode. I see about 3.9 volts on A3 , 3.4 volts on A7 with vin at 5.1v. pmos s to g is 1.02 volts. Using a 3.7v lipo battery the voltage divider does turn off.
I have the pins gnd through A3 connected from the motino to the weathershield and no other connections.
Any thoughts?
OK, I think you found a "bug" :P
Basically when the voltage is higher than about 4.3-4.5V the Vgs is too large and the PMOS stays ON, it's that sensitive - the Vgs (ON state) for this PMOS is (min -0.4 to max -1V).
To fix this for most cases where we expect a battery range from 3.5 to 5V+ we can replace the 10K pullup on the gate with a 1K, as seen in photo attachment.
But otherwise the PMOS should turn off when a LiPo battery voltage is used, or less than 4.5v.
I have a large batch of WeatherShields with 10K gate pullups, I need to decide whether I want to fix all these by hand :P
I will fix the current batch to replace the 10K with 1Ks. The first batch was only 36 units that are out there in the wild and will likely not need this fix if they run off battery of less than 4.5V.
I've updated the schematic to reflect this change:
(https://farm8.staticflickr.com/7321/16216361830_7a4c380aa6_o.png) (https://flic.kr/p/qGZ6pm)WeatherShield schematic (https://flic.kr/p/qGZ6pm) by Felix Rusu, LowPowerLab.com (https://www.flickr.com/people/15304611@N03/), on Flickr
Hi Felix,
Thanks for checking into this so quickly. As you mention this shouldn't be a problem for me on my lipo batteries. It is good to hear that a simple 1k resistor substitution will fix the problem. I guess for a higher vin over 5v you might need something like an additional transistor to switch on and off the gate - although I am not a hardware engineer but I did see a circuit on another forum with an npn transistor to turn the gate on and off when using a 15v supply.
Analog design is not my forte either, but wouldn't the following work?
4k7 10k
Vin---/\/\/\/---+---/\/\/\/---A3
|
|
A7
No transistors of any kind. A3, A7 are normally input, thus Hi-Z and floating, drawing no power. When measuring, A3 is set to output, low and thus grounding the right side of the R network. While A3 switched to L, a measurement can be taken on A7. I'm hoping that experienced folks say something about the feasibility of this solution.
Quote from: Jim111 on February 16, 2015, 11:50:37 AM
Thanks for checking into this so quickly. As you mention this shouldn't be a problem for me on my lipo batteries. It is good to hear that a simple 1k resistor substitution will fix the problem. I guess for a higher vin over 5v you might need something like an additional transistor to switch on and off the gate - although I am not a hardware engineer but I did see a circuit on another forum with an npn transistor to turn the gate on and off when using a 15v supply.
Yes a transistor would work but would increase the BOM and take more space. May be a consideration for R2. But this divider will saturate the range of A7 when exceeding 3.3V (ie when VIN is about 5.3V or so). So it's really meant to be used only with batteries under 5V. The reasoning behind that is that the larger VIN is the less efficient it becomes for the Moteino linear regulator.
Quote from: kobuki on February 16, 2015, 12:18:03 PM
Analog design is not my forte either, but wouldn't the following work?
4k7 10k
Vin---/\/\/\/---+---/\/\/\/---A3
|
|
A7
Not really, you would sink current into A3 and A7 when in HI-Z, depending on how high the voltage then it could be a LOT :)
Well, yeah. Good ol' Jeelabs has been through it and back...
http://jeelabs.org/2013/05/17/zero-powe-battery-measurement/
http://jeelabs.org/2013/05/18/zero-power-measurement-part-2/
That circuit with the MOSFET is awfully familiar from a certain design :-X
Yep, great articles.
Quote from: kobuki on February 16, 2015, 03:12:25 PM
Well, yeah. Good ol' Jeelabs has been through it and back...
http://jeelabs.org/2013/05/17/zero-powe-battery-measurement/
http://jeelabs.org/2013/05/18/zero-power-measurement-part-2/
That circuit with the MOSFET is awfully familiar from a certain design :-X
Quote from: A on February 25, 2014, 09:14:15 PM
I'm thinking of using a mosfet off of D3 to turn on and off all of the non-1-wire sensors. Anyone see an issue with this? I might even add in a second fet in the style of http://jeelabs.org/2013/05/18/zero-power-measurement-part-2/ to rework the battery sensor pin.
Felix, and anyone else who wants to chime in, do you have a preferred SMD mosfet? It looks like p-channel is ideal for the battery voltage sensing, but I am more flexible for the sensor power.
It sure does look familiar ;)
Did changing the resistor from 10k to 1k have any effect on the voltage reading that one would see on the analog input?
I have a moteino & weathershield running from USB (so presumably 5V DC though I don't have my multimeter handy) and running the WeatherShield sketch. I see the following output:
************ Si7021 *********************************
C: 3134 F: 8843 H: 64% DID: 21 BATT: 966
************ BMP180 *********************************
provided altitude: 218 meters, 716 feet
C: 31.46 F:88.63
abs pressure: 999.87 mb, 29.53 inHg
relative (sea-level) pressure: 1026.15 mb, 30.31 inHg
computed altitude: 218 meters, 716 feet
*****************************************************
A BATT reading of 966 indicates 9.66V DC? If so, that seems far too high. Or is the analog reading directly in V DC?
(I just bought 8 of the moteino units & weathershields so am guessing I have modified shields)
966 means 966 out of 1023, or 95% of acceptable range.
The ratio of the resistor voltage divider of the voltage reader is BATT > 4.7K > A7 (this reads your 966) > 10K > GND.
The resistor divider is there to make sure your voltage is below 3.3V which is the voltage the Moteino runs at. If you pass in a voltage more than that your analog range will max out.
Hmmm, this explains a lot.
I started off with Motes and ds18b20 sensors, powered from a 9V PP9 battery. I was getting months of battery life.
I "upgraded" to the weathershield, and now my battery life is less than two weeks.
Recommendations?
Ross,
The sensors on the weather shield are very low power even if you don't do anything. There is a mosfet driven battery monitor on the WS which is 0 power unless you pull down A3 to enable it. Make A3 hi-z (input) to disable the battery monitor. I don't see any reason other than code not being low power that would cause a weather shield to draw any significant amounts of power.
Quote from: rosswakelin on May 26, 2015, 03:27:31 AM
Hmmm, this explains a lot.
I started off with Motes and ds18b20 sensors, powered from a 9V PP9 battery. I was getting months of battery life.
I "upgraded" to the weathershield, and now my battery life is less than two weeks.
Recommendations?
Are you still powering your Mote from a 9V battery? If so, it's no wonder that the battery life is so short.
Weathershield can NOT be powered from a 9V source due to it's 'switchable' battery monitor. With a 9V source, the PMOS transistor is ALWAYS biased on and, as a result, you're pulling a constant 3.5mA from your battery (2.8mA due to the 1.5K+1K gate network, and 1.3mA due to the 4.7K that is overdriving the A7 pin). And this increased power is just due to this circuit alone. You'd have to modify or, at least, remove the battery monitor circuit and it's associated resistors to use the Weathershield with Vin=9V.
Tom
Huh, just noticed this thread as I was going to post something similar. I'd been seeing much higher than expected power usage due to the voltage measurement circuit, and intended to do some detailed analysis to figure out what was going on, but the hard work has already been done. :-)
Since I'm running these off of 4 AA, I'm going to exceed the threshold voltage even with the described modification. For me, the Weathershield proto area works out quite well to put on a transistor to fully switch the measurement circuit; pull the pin from the connecting header on A3 (so it is disconnected from the Moteino), then I put in a BC547 with a 1K bias resistor from A2, which now switches the circuit.
There's an associated problem for me with the measurement: the voltage divider doesn't provide enough range for these cells (max of 4.8V, as I recall).
It occurs to me now that I might as well put my own divider in the proto area, easier than switching around the SMT resistors to adjust the existing divider.
Felix, I'm not sure what to suggest for the Weathershield; in a sense it already supports the modifications I need for higher voltage operation (due to the proto area). A note on the product description page mentioning the voltage 'limit' would be nice.
If I were to make a suggestion for a 'V2', at the moment it would just be to ask that VIN and A0-A3,A7 had convenient pads next to the proto area, and the built in voltage circuit had some cuttable links to allow it to be disabled.
Ideally, yes, I'd like it to support low-power measurement for the full Moteino regulation range.
In any case, this is a cool board, the sensors are great and I do have the thing running at ultra low power. I'm trying out environmental sensor nodes based on the Weathershield, and a Weathershield/Moteino sandwich makes a lovely form factor, much tidier than breadboarding everything. Nice stuff. I just now need a case with some appropriately positioned vents.
Quote from: kalbanowski on May 27, 2015, 01:10:54 PM
Huh, just noticed this thread as I was going to post something similar. I'd been seeing much higher than expected power usage due to the voltage measurement circuit, and intended to do some detailed analysis to figure out what was going on, but the hard work has already been done. :-)
Since I'm running these off of 4 AA, I'm going to exceed the threshold voltage even with the described modification. For me, the Weathershield proto area works out quite well to put on a transistor to fully switch the measurement circuit; pull the pin from the connecting header on A3 (so it is disconnected from the Moteino), then I put in a BC547 with a 1K bias resistor from A2, which now switches the circuit.
There's an associated problem for me with the measurement: the voltage divider doesn't provide enough range for these cells (max of 4.8V, as I recall).
It occurs to me now that I might as well put my own divider in the proto area, easier than switching around the SMT resistors to adjust the existing divider.
Felix, I'm not sure what to suggest for the Weathershield; in a sense it already supports the modifications I need for higher voltage operation (due to the proto area). A note on the product description page mentioning the voltage 'limit' would be nice.
If I were to make a suggestion for a 'V2', at the moment it would just be to ask that VIN and A0-A3,A7 had convenient pads next to the proto area, and the built in voltage circuit had some cuttable links to allow it to be disabled.
Ideally, yes, I'd like it to support low-power measurement for the full Moteino regulation range.
In any case, this is a cool board, the sensors are great and I do have the thing running at ultra low power. I'm trying out environmental sensor nodes based on the Weathershield, and a Weathershield/Moteino sandwich makes a lovely form factor, much tidier than breadboarding everything. Nice stuff. I just now need a case with some appropriately positioned vents.
To my mind, a switch to control a battery measurement is unnecessarily complicated/power consuming. I generally use very high value resistors with a 0.01uF cap at the analog input pin to handle the capacitive load when the analog mux is switched over. You can keep the current below 1uA and still get reliable readings.
I almost always use a 3.3M resistor from the analog pin to ground and then tailor the upper resistor to match the intended battery supply. So, for example, with the cited case of 9V, I'd use a 6.8M resistor which gives me an almost direct reading in 10mV units at the ADC (10.10 volts would be full scale 1023 reading). For the 4AAs, I'd use 2.7M and 6.0V would be full scale 1023 counts (actually I'd probably allow for some margin and use 3.3M, but you get the idea). For a 5V supply I use 1.8M and can divide the ADC value by 2 to get 10mV units.
Last I checked, this comes to 1uA of current without any hassle...
For the Weathershield you can remove the transistor and the two gate resistors, jumper the Drain and Source pads, and replace the divider resistors appropriately. I think you'll find that an 805 cap will piggy back nicely on the resistor.
Tom
PS: I agree it's a cool board.
Couldn't agree more about the battery measurement without switch. In fact you don't even need the capacitor if you call analogRead twice as described for example here: http://forum.arduino.cc/index.php?topic=169000.10;wap2
That's the approach I'm using (also with huge resistors). I generally like to use as few hardware components as possible esp since I don't create custom PCB's.
Good points and suggestions, thanks TomWS for actual numbers. When I switch to passives only I will need to fight the other camp who wants the switch because a constant drain of *anything* bothers something in their brain ::)
Quote from: Felix on May 28, 2015, 07:33:07 AM
...I will need to fight the other camp who wants the switch because a constant drain of *anything* bothers something in their brain ::)
Yes, I can understand that, after all, in the 9V case, with 1uA constant drain, the battery life will be reduced by a factor of 1/565000...
It just occurred to me that those who are REALLY concerned about every last uA won't (or shouldn't) be using Vin anyway...
@Joelucid, if you are willing to do multiple analogRead()s or only have the one ADC input and can leave the mux selecting the single source, yes, you can get away without some buffering on the input. In my case, I always measure VCC in addition to the divider so that I can accurately scale the divider input (VCC is not always 3.3V ;)
T
A dedicated battery monitor chip might be an alternative. But I'd have to do the research to pick one, cost might be magnitudes more, and the protocol to read it might be another learning barrier. I think the resistor + 0.1uF method works fine, I usually stayed below 1Meg so far but your findings are promising.
If you go the large resistor route you could add battery monitoring to the regular Moteino design. Given the huge resistance you wouldn't be sacrificing an analog input: If an application needs the pin for other purposes the input would easily overpower the divider output. Obviously you'd have to size the resistors to enable the full possible VIN range, but that would still be enough to detect a dying battery.
It would be really useful to have battery monitoring part of the basic package, esp with the battery focus of Moteino!
While Moteinos are battery friendly they were not specifically designed for exclusive battery operation, hence I did not include a monitor onboard. We would be huge debate on the forum about the implementation, the resistors chosen, people would complain that it doesn't work for them and they want different values/range covered, or they want jumpers to disable it, or they want it on a different analog pin or this or that and it never ends.
Hence monitors were offered in separate boards like the MotionMote, PowerShield, and WeatherShield. Also some of these boards have proto areas where you can make your own if you'd like.
Over time I have received a ton of great suggestions to include all kinds of features in the basic package, all tempting. Looking at the big picture, it's really hard to satisfy all the needs. Moteino will likely stay largely the same over its existence. I think addon boards is where such options are more feasible and appropriate. It's separation of concerns.
I have to agree with Felix on this one, which pin would you use? What divider resistor would you use? A filter cap would be required to my mind, but then this would eliminate the possibility of using the pin as a GP pin for some other purpose. Adding the three components external to Moteino isn't really a problem, even on a standalone config.
Along these lines, even adding the components manually to a WeatherShield would be less of a problem than the current implementation.
Tom
I just built a water thermometer for the lake at the weekend house today. It could all be so simple. I have wireless boot and I bought a water resistant DS18B20. So I would only need to solder 4 pins: vin, gnd, and 2 wires for the sensor and program wirelessly. Easy. The board would be completely flat.
Instead I have to solder on the headers, do a ISP programming of the bootloader, add a board to add the vin measurement divider etc. etc. This makes it complicated and much larger than it really needs to be. Or I could purchase PowerShield and double the cost of the project.
I used 3 megaohm : 6 megaohm today since I'm planning to use a 9v battery.
Here's how it would work for everybody:
Use 1 : 6 megaohm to cover the whole range of the voltage regulator which is clearly the general purpose range. Use A7 which doesn't interfere with digital in/outputs. Don't use a cap - not needed just call analogRead twice. Layout the board such that if somebody doesn't like it they can sever the connection between divider and A7 - similar to the USB adapter.
The atmega328p allows me to measure vcc natively. So really the need for the voltage divider originates from the fact that the Moteino comes with a voltage regulator and vcc breaks down very rapidly in the end. Just view the divider as part of the power system of the Moteino and it really belongs in the basic package.
Now if somebody needs a special implementation, or a cap, or finer resolution etc. Fine, let them add their own circuit on an add-on board.
Then I would only need to convince Felix to preburn my bootloader for my Moteinos ;)
Joe
I bought 8 moteino boards & 8 weathershields, putting each of them in rooms in the house, 1 outside and 1 in the fridge! Just doing some experiments to see if I can determine patterns of behaviour and maybe generate alerts if the behaviour changes. I do notice humidity in the bathroom sensor jumps up 10% within 1 minute when someone takes a shower so should be possible to detect these kinds of activities.
The systems are powered from 9V batteries as they are in locations that don't have powerpoints nearby and I want them to be unobtrusive so they are in small plastic boxes. I did manage to log temp, humidity & pressure for a week or 2 but now have some questions:
1) I am using the code obtained here but always get a battery reading of 1023.
pinMode(A3, OUTPUT);
digitalWrite(A3, LOW);
battV=analogRead(A7);
pinMode(A3, INPUT);
I posted a related question on May 16th when I was powering the system off USB and hadn't tested on 9V but then I was getting a reading of 966. With 9V it seems the battery detection isn't working, or at least not like I thought it would. Anyone know why? I did read somewhere about a resistor being changed from 1k to 10k and as I bought the boards recently I would assume I have the newer boards which should have fixed any problem? Or will the battery detection just not work with a 9V input as it is? If not, what changes could I make?
2) Out of 8 systems, 3 stopped working about 1 week after the battery went flat. I still have 5 going after about 2 weeeks but I assume they won't run a lot longer. I see a posting from TomWS saying "Weathershield can NOT be powered from a 9V source due to it's 'switchable' battery monitor. With a 9V source, the PMOS transistor is ALWAYS biased on" but I am also a bit confused by that - isn't the A3 enable/disable & the new resistor supposed to fix that?
I want to try increasing the battery life as much as possible so would like to understand this more and make whatever change is needed.
3) Anyone have any experience modifying the weathershield one step further to turn the whole board off when not in use? I am (with the present version at least) measuring every 1 minute and am trying not to poll less often than this as I will miss events. In fact I was thinking of adding a light sensor to the unit in the fridge and including light readings but I guess most people don't leave the fridge open for a whole minute so if I could get better battery life then I would even experiment with 30 seconds updates. Looking at the specs for the si7021 it seems that giving it 5 seconds to settle down before taking the reading might be plenty so I could have the board turned off until 5 seconds before the readings are needed.
Quote from: DPBaker on June 19, 2015, 11:50:04 PM
<snip>
The systems are powered from 9V batteries
I've commented elsewhere on using 9V batteries - very energy inefficient unless you need a voltage above 5V.
I think you should read the thread on the Weathermote thoroughly. Here are the high points that you should understand:
1. The resistor 'fix' to A3 enable only hid the problem if your Vin is between 3.3V-5V. It completely fails on any voltage above 6V.
2. Understand how the ADC works, specifically how the reading is a ratio of (Ain/Aref)*1023, where Aref is typically, but not always, 3.3V.
3. The thread discusses appropriate resistors to use if you do have a 9V battery. You need to replace the onboard resistors for such a high Vin.
4. The Weathermote circuitry is such very low current that it's probably less than 1% of your sleeping budget in the ideal case. Given that your batteries are dying in days tells me that you have some work to do before you are close to the ideal case. Net: it is not necessary to 'turn off' the Weathermote.
5. Are you powering down (ie sleeping) between measurements?
Tom
1,2, & 3 - Thanks for the info. There is a lot going on in this topic with discussion of just using resistor divider, additional transistor and just changing the resistor values in the existing circuit - mention of also changing the resistor for the FET pullup as well. So, I just want to make sure I am not getting confused.
Only 3 of the batteries have died in less than 2 weeks, but here in Asia isn't not uncommon to get fake or used batteries sold as new so wouldn't surprise me if the actual lifetime is much higher - the other 5 are still going ok although until I get the voltage reader working I can't really monitor to see the battery decline. Could measure with voltmeter but I don't really want to disturb the sensors while I am collecting good data.
I am sleeping between readings. My multimeter might not be accurate but as far as I can tell I am drawing 23mA when system is on for a few seconds every minute and about 0.4uA in between readings.
Good news re the weathershield having such low current though, so at least I can eliminate that.
I think I will place an order for some battery holders for 3 x AA cells and see how that goes - at least then I don't have to mess with the battery monitor circuitry and can just concentrate on code for the time being.
Quote from: DPBaker on June 20, 2015, 11:28:06 PM
<snip>
I think I will place an order for some battery holders for 3 x AA cells and see how that goes - at least then I don't have to mess with the battery monitor circuitry and can just concentrate on code for the time being.
That's a good practical approach.
Tom
I finally managed to find a local source of battery holders for 18650 batteries, so I have replaced my 9V batteries with these items (batteries are easy to find, battery holders no so much so).
Seems to have worked, and battery life has stretched out again.
Thanks for the useful info everybody.
What vendor makes your battery holders? The ones available locally look similar to what's available on Amazon, wires/connectors seem a bit flimsy. The Keystone holders look more substantial but I haven't found a local source for instant gratification.
The holders are not vendor labelled, but the wires appear strong enough, and they only get touched when I need to recharge/replace the batteries.
Just remember that local for me is New Zealand.....
Quote from: jra on June 26, 2015, 03:43:19 PM
What vendor makes your battery holders? The ones available locally look similar to what's available on Amazon, wires/connectors seem a bit flimsy. The Keystone holders look more substantial but I haven't found a local source for instant gratification.
I've purchased both the Keystone and these from Amazon (http://www.amazon.com/gp/product/B00FHKL3KY). You are right, the ones from Keystone are more substantial, much better quality, but, according to the Keystone datasheet, won't accept the slightly longer 18650s with the protection circuit. I'll admit that I didn't try them because the Keystone's I bought had surface mount tabs and, so far, I've needed holders with wires.
I did find that if I drilled out the rivet on both ends of the, ahem, 'inexpensive' ones, I could fit a 1/4" x 2-56 phillips head screw with star washers on both sides, using the head on the inside as the battery contact, that the connection reliability is much better - just make sure you use zinc plated screws to prevent electrolytic corrosion.
Also, a short length of ribbon or even electrical tape wrapped around the battery to serve as a pull handle makes it much easier to remove the battery - otherwise it is VERY hard to remove.
Tom