Sensor board w/ liPo charger and fuel gauge +BMP180 +HTU21
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Does anybody have any comments about the new version of the universal sensor board, the ceech board?
Here are some of the new features:
LTC4067 Li-Po, Li-ion battery charger with voltage and current measurements,
XC6210, 700mA voltage regulator with 35uA supply current,
BMP180 pressure and altitude sensor,
HTU21 temperature and humidity sensor,
24LC512 EEPROM.
It is a work in progress and is not quite finished yet. -
I am actually considering something similar. But I am contemplating skipping the charger part, and leave a connector for the charger to be connected externally when needed (I already have one of these). And use sockets/headers to be able to re-use the Arduino modules, RF and sensors.
@Anticimex Do you have any experience with that charging board that you've mentioned? It uses MCP73861, right? I'm asking if you tried to charge a battery with a solar cell using this module? Because that is my main goal in developing this board. To be able to properly charge a lithium cell using solar power. MCP73861 is a nice chip, I chose the LTC4067 because I would like to monitor the current that flows to the battery.
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@ceech Looks promising. A little worried about the price when using a HTU21.... A suggestion from experience with the current ceech board: add a little more information on the silk screen. Especially for the breakout headers..
@AWI Which humidity sensor do you think would be more appropriate?
I'll post a 3D picture with more detailed description of the current version of the board under its thread. -
@Anticimex Do you have any experience with that charging board that you've mentioned? It uses MCP73861, right? I'm asking if you tried to charge a battery with a solar cell using this module? Because that is my main goal in developing this board. To be able to properly charge a lithium cell using solar power. MCP73861 is a nice chip, I chose the LTC4067 because I would like to monitor the current that flows to the battery.
@ceech I am afraid not. I have just bought myself a pair of cells and that charger as a kickoff to investigate what power source I should use. I am also considering 9V cells and button cells. Solar power is not really available to me where I live at the moment so I have not consider that as a source yet I am afraid. Currently, I believe I am going for LiPo on the more "active" nodes (temp/humidity/motion) and a 9V cell for the more "passive" (soil/door/window). And I think I want to keep the charger off-board to keep the boards simple and see if I can get my theoretical sample based voltage measurement circuit to work independent of the source used.
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@AWI Which humidity sensor do you think would be more appropriate?
I'll post a 3D picture with more detailed description of the current version of the board under its thread. -
@ceech I am afraid not. I have just bought myself a pair of cells and that charger as a kickoff to investigate what power source I should use. I am also considering 9V cells and button cells. Solar power is not really available to me where I live at the moment so I have not consider that as a source yet I am afraid. Currently, I believe I am going for LiPo on the more "active" nodes (temp/humidity/motion) and a 9V cell for the more "passive" (soil/door/window). And I think I want to keep the charger off-board to keep the boards simple and see if I can get my theoretical sample based voltage measurement circuit to work independent of the source used.
@Anticimex You went all this way just to eliminate leaking? That is impressive. Are you going to implement this on your board or is this only a test? Did you also test the current leakage in voltage divider circuit connected all the time? What is the difference?
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@AWI Which humidity sensor do you think would be more appropriate?
I'll post a 3D picture with more detailed description of the current version of the board under its thread. -
@Anticimex You went all this way just to eliminate leaking? That is impressive. Are you going to implement this on your board or is this only a test? Did you also test the current leakage in voltage divider circuit connected all the time? What is the difference?
@ceech said:
@Anticimex You went all this way just to eliminate leaking? That is impressive. Are you going to implement this on your board or is this only a test? Did you also test the current leakage in voltage divider circuit connected all the time? What is the difference?
Well, it's not that complicated :)
No, I have not made any comparisons whatsoever. But I am pretty confident it will be less leaky than a voltage divider. That I simply won't use because the higher resistance you use, the more noise you get, which will in the end translate into a meaningless measurement. But I have not made any real-world measurements for comparison, as this is so use-case dependent. Also for a voltage divider, the current draw is small, and depending on the nodes power consumption, that current may, or may not, be negligible. -
Why not just use ordinary Alkaline AA batteries? Cheap, available everywhere in any store, excellent self-discharge etc. Couple that with a suitable voltage regulator (boost/step-up) that can start as low as 0.6-0.7V and you should be good to go even with a single AA/AAA.
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Why not just use ordinary Alkaline AA batteries? Cheap, available everywhere in any store, excellent self-discharge etc. Couple that with a suitable voltage regulator (boost/step-up) that can start as low as 0.6-0.7V and you should be good to go even with a single AA/AAA.
@bjornhallberg the impression I get on the forum from people doing that is that they get roughly one month of lifetime of a charge. To me that is simply not good enough. Not by a long shot.
Do you feel secure today? No? Start requiring some signatures and feel better tomorrow ;)
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@bjornhallberg the impression I get on the forum from people doing that is that they get roughly one month of lifetime of a charge. To me that is simply not good enough. Not by a long shot.
@Anticimex I've run my sensors, including SR-501, DS18B20 and DHT22, on AA batteries for 4-6 months with little or no issues. And that is without a regulator. What happens eventually, with the DS18B20 for instance, is that the temp readings keep declining with the declining voltage. I'm actually very surprised that the SR-501 is still alive. The SR-501 sensor itself leaks like 50uA and I have a voltage divider to read the voltage (but I can't take the reading since the MQTT gateway doesn't seem to work). I read somewhere that that the SR-501 would produce massive false readings with the voltage drop but so far so good.
With a proper regulator you should be good for 1-2 years.
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@Anticimex I've run my sensors, including SR-501, DS18B20 and DHT22, on AA batteries for 4-6 months with little or no issues. And that is without a regulator. What happens eventually, with the DS18B20 for instance, is that the temp readings keep declining with the declining voltage. I'm actually very surprised that the SR-501 is still alive. The SR-501 sensor itself leaks like 50uA and I have a voltage divider to read the voltage (but I can't take the reading since the MQTT gateway doesn't seem to work). I read somewhere that that the SR-501 would produce massive false readings with the voltage drop but so far so good.
With a proper regulator you should be good for 1-2 years.
@bjornhallberg Ok, well that sounds much more reasonable to me then :)
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@Anticimex I've run my sensors, including SR-501, DS18B20 and DHT22, on AA batteries for 4-6 months with little or no issues. And that is without a regulator. What happens eventually, with the DS18B20 for instance, is that the temp readings keep declining with the declining voltage. I'm actually very surprised that the SR-501 is still alive. The SR-501 sensor itself leaks like 50uA and I have a voltage divider to read the voltage (but I can't take the reading since the MQTT gateway doesn't seem to work). I read somewhere that that the SR-501 would produce massive false readings with the voltage drop but so far so good.
With a proper regulator you should be good for 1-2 years.
@bjornhallberg Have you tried to compare regulated and non-regulated supply? It would be reasonable to assume you can get more out of the batteries if you can suck them down to 0.5-0.6V. But the step-up regulators are quite "leaky" so will that really translate to a longer runtime in the end? The regulator will be on even if the node is sleeping (and efficiency drops with current drop). So perhaps (depending on usage of course) a regulated supply will actually drain the batteries faster and the end result is that it causes shorter runtime even if more juice is pulled from the cells.
I have not yet set up a proper test environment for this myself.
I was considering having a regulator you could switch off. So that the Arduino itself runs unregulated but the sensors uses regulated power. Then you could turn off the regulator when sleeping. Like one of these.
A cool variant would be to have a regulator that turns itself on when battery voltage drops below a known safe level. The trick is to implement a power rail that can switch from unregulated to regulated supply. The switching can just be done with a comparator. But feedback between regulator output and input is a bad idea I suppose...Do you feel secure today? No? Start requiring some signatures and feel better tomorrow ;)
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@bjornhallberg Have you tried to compare regulated and non-regulated supply? It would be reasonable to assume you can get more out of the batteries if you can suck them down to 0.5-0.6V. But the step-up regulators are quite "leaky" so will that really translate to a longer runtime in the end? The regulator will be on even if the node is sleeping (and efficiency drops with current drop). So perhaps (depending on usage of course) a regulated supply will actually drain the batteries faster and the end result is that it causes shorter runtime even if more juice is pulled from the cells.
I have not yet set up a proper test environment for this myself.
I was considering having a regulator you could switch off. So that the Arduino itself runs unregulated but the sensors uses regulated power. Then you could turn off the regulator when sleeping. Like one of these.
A cool variant would be to have a regulator that turns itself on when battery voltage drops below a known safe level. The trick is to implement a power rail that can switch from unregulated to regulated supply. The switching can just be done with a comparator. But feedback between regulator output and input is a bad idea I suppose...@Anticimex Sorry, I don't have any long time data to offer. So I also don't know if bothering with the SHDN / EN pins (where applicable) is actually worth it. Quiescent current is usually pretty low on some of the better regulators (like TPS61221, LTC3525 etc) so I wonder if it is worth tampering with?
I still think you will gain a few months of run-time using a regulator. Still, no big savings there. The main reason (for me at least) to explore regulators is to enable sensors that would otherwise malfunction as the voltage drops. I.e. most of the common sensor we use (DHT22, DS18B20, Motion). Particularly the DS18B20 has been spotty for me.
Another point is to be able to build really compact sensors that use only one AA/AAA. Not even the nrf24 / atmega would work at 1.5V (and dropping) after all.
Also, according to my latest calculations, a separate pcb with the TPS61221 will cost about $1.75 in materials. So, it wont break the bank.
I wish we could fast-track the entire project a bit and come up with a standard form factor like LowPowerLabs or Harizanov where we could make shields that just plug. Btw, did you see this on the topic of LiPo batteries:
http://lowpowerlab.com/blog/2015/02/03/chinese-lithium-cells-freezing/ -
@bjornhallberg Have you tried to compare regulated and non-regulated supply? It would be reasonable to assume you can get more out of the batteries if you can suck them down to 0.5-0.6V. But the step-up regulators are quite "leaky" so will that really translate to a longer runtime in the end? The regulator will be on even if the node is sleeping (and efficiency drops with current drop). So perhaps (depending on usage of course) a regulated supply will actually drain the batteries faster and the end result is that it causes shorter runtime even if more juice is pulled from the cells.
I have not yet set up a proper test environment for this myself.
I was considering having a regulator you could switch off. So that the Arduino itself runs unregulated but the sensors uses regulated power. Then you could turn off the regulator when sleeping. Like one of these.
A cool variant would be to have a regulator that turns itself on when battery voltage drops below a known safe level. The trick is to implement a power rail that can switch from unregulated to regulated supply. The switching can just be done with a comparator. But feedback between regulator output and input is a bad idea I suppose...@Anticimex Just thinking out loud. Looking at the schematics of the predecessor of this board. There is a mosfet circuit connected to D4. Couldn't you use this to power up an external. regulator or step-up?
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@Anticimex Just thinking out loud. Looking at the schematics of the predecessor of this board. There is a mosfet circuit connected to D4. Couldn't you use this to power up an external. regulator or step-up?
@AWI yea, but the problem is not activating the regulator. That is a simple IO operation. The problem I think is the output of the regulator, if you want it to power the Arduino itself. And you probably do, since the Arduino packs up probably before your sensors. I need to study some more before I got a plan for that, but I also have a LOT of other things to do so don't expect me to provide the One Solution to it in the coming weeks ;)
Do you feel secure today? No? Start requiring some signatures and feel better tomorrow ;)
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@AWI yea, but the problem is not activating the regulator. That is a simple IO operation. The problem I think is the output of the regulator, if you want it to power the Arduino itself. And you probably do, since the Arduino packs up probably before your sensors. I need to study some more before I got a plan for that, but I also have a LOT of other things to do so don't expect me to provide the One Solution to it in the coming weeks ;)
@Anticimex Switching the Arduino is probably not a good idea :) but powering up the voltage sensitive sensors with a mosfet switched step-up converter is an option?
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@Anticimex Switching the Arduino is probably not a good idea :) but powering up the voltage sensitive sensors with a mosfet switched step-up converter is an option?
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The main reason why I was dragged to the LTC4067 is the fact that it has so called Power path technology. It only uses the battery if there is no other available source of power. The benefit is much longer battery lifetime. It also has a proper 2A Lithium charger. Last but not least is the current monitoring, which can be translated into battery state of charge, which is another thing that interests me.
I chose the voltage regulator for the fact that is fairly efficient and powerful even for ESP8266 modules and as simple as possible to implement. It only uses 35uA, which is as low as I ever saw. And the LTC4067 has Suspend mode that only uses a couple of uA as well.
@tbowmo Prices for the HTU21 are lower, for me at least. And since the pinout is the same it is all for the better.
I'll put some thought into the separate power options. The first thing that can be fairly simply done is to power the Atmega328 from the battery, and the sensors from the regulator.
