💬 Battery Powered Sensors
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Another battery related question that I really do not understand.
Are there different versions on how to read battery consumption?I see some sketches uses:
long readVcc() { long result; // Read 1.1V reference against AVcc ADMUX = _BV(REFS0) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1); delay(2); // Wait for Vref to settle noInterrupts (); // start the conversion ADCSRA |= _BV (ADSC) | _BV (ADIE); set_sleep_mode (SLEEP_MODE_ADC); // sleep during sample interrupts (); sleep_mode (); // reading should be done, but better make sure // maybe the timer interrupt fired while (bit_is_set(ADCSRA,ADSC)); result = ADCL; result |= ADCH<<8; result = 1126400L / result; // Back-calculate AVcc in mV```However some (like the original one in this thread) uses:
int sensorValue = analogRead(BATTERY_SENSE_PIN);Is it due to different libraries or maybe it is the same but just programming wise different?
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If you are using the first sketch you dont have to use a seperate pin to measure the input voltage. There are also no resistors.
You can run this on a bare ATmega with minimal hardware.
@gloob thanks!
One would think running with no resistors and not using a separate PIN would be better.@hek or @mfalkvidd , any comments as to why the original sketch is preferred over the other 'way' in this article?
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@gloob thanks!
One would think running with no resistors and not using a separate PIN would be better.@hek or @mfalkvidd , any comments as to why the original sketch is preferred over the other 'way' in this article?
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@hek , I've read that post several times :)
Since it was so outdated (2 years) I naturally assumed the 'battery powering article' was a newer way to do it (especially since mys2.0).
Also, the post you linked to is attributed if you use no voltage regulator.
And in the article this is also one of the things you are recommended to remove, hence making it even more confusing as to why the article describes another way than the post. -
i just want to get this once and for all, so others coming by gets it directly instead of going through all the 2 threads posts, please correct me if i am wrong:
1- using the voltage divider is needed if there is a voltage regulator / booster where where VBatt != Vcc.
2- using the voltage regulator is not needed if the voltage regulator is removed / no booster is used (powering directly from 2 x AA batteries) where VBatt == Vcc.*I've noticed the 2nd method requires inputting battrie's DMM measured values vs arduino ones for correction, is this a down side if you need to change the battery later on ? or is it just programmed once ? and does the 1st method rquirs these corrections too ?
Cheers
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i just want to get this once and for all, so others coming by gets it directly instead of going through all the 2 threads posts, please correct me if i am wrong:
1- using the voltage divider is needed if there is a voltage regulator / booster where where VBatt != Vcc.
2- using the voltage regulator is not needed if the voltage regulator is removed / no booster is used (powering directly from 2 x AA batteries) where VBatt == Vcc.*I've noticed the 2nd method requires inputting battrie's DMM measured values vs arduino ones for correction, is this a down side if you need to change the battery later on ? or is it just programmed once ? and does the 1st method rquirs these corrections too ?
Cheers
@Meshx86
actually, you need a voltage divider if the voltage to be measured is above the maximum allowed by the processor at the speed you are running it.If Vcc is 5V, then any voltage above 5V should be measured via a voltage divider.
If Vcc is 3.3V same principle, but you could get away with measuring 5V directly (would not kill the processor), but your values may be off. -
@Meshx86
actually, you need a voltage divider if the voltage to be measured is above the maximum allowed by the processor at the speed you are running it.If Vcc is 5V, then any voltage above 5V should be measured via a voltage divider.
If Vcc is 3.3V same principle, but you could get away with measuring 5V directly (would not kill the processor), but your values may be off.@GertSanders following the instructions of this post suggest using Alkaline batteries (apparently Li-ion aren't a good idea for sensor nodes ?! plus they are expensive), the optimal solution would be using 2 x AA batteries as some ans this post suggested.
I believe there is no way 2 x AA batteries in series would measure anywhere near 3.3v, the max i measured with brand new batteries was 3.2v.
my major concern is:
would i still need to the do the voltage corrections when using the voltage divider ? if so, does that need to be reprogrammed every time you replace the battery ? -
@GertSanders following the instructions of this post suggest using Alkaline batteries (apparently Li-ion aren't a good idea for sensor nodes ?! plus they are expensive), the optimal solution would be using 2 x AA batteries as some ans this post suggested.
I believe there is no way 2 x AA batteries in series would measure anywhere near 3.3v, the max i measured with brand new batteries was 3.2v.
my major concern is:
would i still need to the do the voltage corrections when using the voltage divider ? if so, does that need to be reprogrammed every time you replace the battery ?@Meshx86
No problem to ask. I use the intern measurement method, which uses the internal 1.1V reference of the atmega328, so even if the Vcc value changes from 3.2V -> 2.6V, the reference will always be 1.1V, and the internal method allows you to calculate the actual measured battery voltage based on a difference with the reference, even with a declining value on Vcc (if powered by the same batteries). -
@Meshx86
No problem to ask. I use the intern measurement method, which uses the internal 1.1V reference of the atmega328, so even if the Vcc value changes from 3.2V -> 2.6V, the reference will always be 1.1V, and the internal method allows you to calculate the actual measured battery voltage based on a difference with the reference, even with a declining value on Vcc (if powered by the same batteries).@GertSanders sorry mate, am more of a software guy..
according to the lib i've seen and @Yveaux's example for the internal method, at the begining you need to define a corrective value :
const float VccCorrection = 1.0/1.0; // Measured Vcc by multimeter divided by reported Vcc Vcc vcc(VccCorrection);is this necessary for an accurate reading ? and is the corrective value need to be just entered once (like a calibration per arduino) or need to be reconfigured every time you replace a battery ?
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Good article/site on why Alkaline is the best way to go for Mysensors nodes :)
http://batteryuniversity.com/learn/article/elevating_self_discharge -
@GertSanders sorry mate, am more of a software guy..
according to the lib i've seen and @Yveaux's example for the internal method, at the begining you need to define a corrective value :
const float VccCorrection = 1.0/1.0; // Measured Vcc by multimeter divided by reported Vcc Vcc vcc(VccCorrection);is this necessary for an accurate reading ? and is the corrective value need to be just entered once (like a calibration per arduino) or need to be reconfigured every time you replace a battery ?
@Meshx86
The corrective value is needed every time you change a battery, AND if you need high accuracy.
On my battery based nodes I do not have a need for absolute accuracy, I just need to see the trend of the Vcc value.
Changing the battery happens every 12-24 months (depends on the use), so I'm not very interested in absolute accuracy. If you need real accurate measuring, I would suggest a real Analog-To_Digital chip. -
@Meshx86
The corrective value is needed every time you change a battery, AND if you need high accuracy.
On my battery based nodes I do not have a need for absolute accuracy, I just need to see the trend of the Vcc value.
Changing the battery happens every 12-24 months (depends on the use), so I'm not very interested in absolute accuracy. If you need real accurate measuring, I would suggest a real Analog-To_Digital chip. -
@GertSanders thanks , i think accuracy isn't a deal breaker, i believe everyone's concern is to just know when the batteries need to be replaced (hopefully that can be done without specifying the voltage correction).
@Meshx86 ok, being quoted so many times I can also add my 5 cents :smile:
The correction factor is optional. You can use it to improve the measured voltage, as the internal voltage reference is only accurate up to so many percentage (have to look up the number). It is unique to the arduino used.
This factor should however not depend on the batteries, possibly on environmental factors (e.g. Temperature)http://yveaux.blogspot.nl
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@Meshx86 ok, being quoted so many times I can also add my 5 cents :smile:
The correction factor is optional. You can use it to improve the measured voltage, as the internal voltage reference is only accurate up to so many percentage (have to look up the number). It is unique to the arduino used.
This factor should however not depend on the batteries, possibly on environmental factors (e.g. Temperature)@Yveaux one last, i promise :P
if max battery voltage is actually 3.2v, does that mean that the battery percentage would show 100% for quite sometime before it starts dropping below 3.0v (assuming vmax is set to 3.0) ? or would it increase the inaccuracy gap ?
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@Yveaux one last, i promise :P
if max battery voltage is actually 3.2v, does that mean that the battery percentage would show 100% for quite sometime before it starts dropping below 3.0v (assuming vmax is set to 3.0) ? or would it increase the inaccuracy gap ?
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Good article/site on why Alkaline is the best way to go for Mysensors nodes :)
http://batteryuniversity.com/learn/article/elevating_self_discharge@Nicklas-Starkel The article mostly talks about rechargeable batteries. I prefer non rechargeable Lithium batteries (like coin cells) for their energy density and very low self discharge.
My major concern with (cheap) alkaline batteries is their leakage of aggressive chemicals. I had to trash my first nodes because of this :unamused: -
@Nicklas-Starkel The article mostly talks about rechargeable batteries. I prefer non rechargeable Lithium batteries (like coin cells) for their energy density and very low self discharge.
My major concern with (cheap) alkaline batteries is their leakage of aggressive chemicals. I had to trash my first nodes because of this :unamused:@AWI in the first part it states:
"Primary cells such as lithium-metal and alkaline retain the stored energy best, and can be kept in storage for several years."
So you are correct and between Alkaline and Lithium-metal maybe the latter would be best. :)
I have no experience with coin cells and will do some testing with them as soon as I can.
Since this is the battery article, would you please tell me what you use and how you use it. What you expected and if the batteries lived up to your expectations. Would be cool to know as you've had more experience then me (and many like me)! -
@Nicklas-Starkel The article mostly talks about rechargeable batteries. I prefer non rechargeable Lithium batteries (like coin cells) for their energy density and very low self discharge.
My major concern with (cheap) alkaline batteries is their leakage of aggressive chemicals. I had to trash my first nodes because of this :unamused:@AWI I'm agree with you but coin cells have less capacity. The difference of the self discharge between coin cells and alkaline is not important (1% vs 2%), but the capacity and size are.
Here is a link with the Battery self-discharge rates :
http://www.gammon.com.au/power -
@AWI in the first part it states:
"Primary cells such as lithium-metal and alkaline retain the stored energy best, and can be kept in storage for several years."
So you are correct and between Alkaline and Lithium-metal maybe the latter would be best. :)
I have no experience with coin cells and will do some testing with them as soon as I can.
Since this is the battery article, would you please tell me what you use and how you use it. What you expected and if the batteries lived up to your expectations. Would be cool to know as you've had more experience then me (and many like me)!@Nicklas-Starkel I mostly use a 'large' version lithium cell i.e. Cr123. These were used large in compact camera's and have a huge capacity and very little self discharge. My best example is the sensor in the fridge which measure temp and humidity every 10 secs and sends with nrf24l01 (MySensors of course). This one runs for almost two years now and has a stable 3.02V since the second month.
The coin cells need special care a these have a high 'internal resistance'. You need to be careful with designing the sketch so that the load is as short and light as possible.
There are some of my postings on this site which elaborate on the subject. (I'm on a mobile phone right now...)
