coin-cell (CR2032) powered temperature sensor

[fleinze]

Kind of. I used a different Arduino and now it works.

[fleinze]

@TheoL: The step-up regulator will most likely drain your battery very quickly. It uses a lot of current in "standby-mode" (when Arduino is powered down)!

You can power an Arduino and most sensors directly from battery but you need to disable BOD (brown-out-detection). To do this you need an programmer ("Arduino as ISP"-sketch is sufficient) and set the extended-fuse to 0x07. This can be done with the Arduino-IDE, but you need to edit the boards.txt file.

[carleki]

what about your nodes after several months ?

[fleinze]

@carmelo42 I just changed coin-cell on one of my sensors. It lasted since for 10 months, this is ok for me.

[fleinze]

Measuring the voltage proofed to be worthless for this kind of battery. It is more dependent of the temperature than from anything else.

[carleki]

@fleinze said:

@carmelo42 I just changed coin-cell on one of my sensors. It lasted since for 10 months, this is ok for me.

10 months ? it's perfect :)

Can you provide the modified version of the library to avoid using 4.7k resistor for the Dallas sensor ?

What is for the resistor on the pic ? for the voltage mesurement ?

[fleinze]

@carmelo42

The no-resistor-library can be found here:
https://wp.josh.com/2014/06/23/no-external-pull-up-needed-for-ds18b20-temp-sensor/

The resistors (there are two but the other one is barely visible) are for voltage-measurement. In a later version I got rid of them using this resistor-less method of measurement:
http://provideyourown.com/2012/secret-arduino-voltmeter-measure-battery-voltage/

[Moebius Lutching]

Just found this post https://www.hackster.io/Talk2/temp-and-humidity-sensor-with-a-cr2032-for-over-1-year-580114 showing some details about using a CR2032 to power a sensor node. By my calculations, if the author removed the LED at all the solution would last for over 2 years!

[carleki]

@fleinze said:

@carmelo42

The no-resistor-library can be found here:
https://wp.josh.com/2014/06/23/no-external-pull-up-needed-for-ds18b20-temp-sensor/

The resistors (there are two but the other one is barely visible) are for voltage-measurement. In a later version I got rid of them using this resistor-less method of measurement:
http://provideyourown.com/2012/secret-arduino-voltmeter-measure-battery-voltage/

great :)

Did you change the bootloader ? Which one did you use ?

[Nca78]

Hello,

there are a few improvements you can do to make your CR2032 nodes last longer:

• add a capacitor of 100-200µF in parallel with your battery. Ceramic is better, but I have no problem with nodes using electrolytic capacitors. This will help when there is a peak power consumption from the radio. If you do not put one, voltage will drop quickly and that's probably what is triggering reboot loop on one of your nodes: maybe radio is less efficient and needs to resend more messages. Or maybe your BOD is not updated so it resets when voltage drops at 2.7V...
• in your code, add a sleep command between message sending to give time for your cell to rest, and for the capacitor to recharge. Do it also at the beginning of presentation method and between each message sending in presentation.
• use a better sensor that can accept a lower voltage, they are more expensive that DS18 but they can work down to 2V and use much less current: BMP180/280 if you want to measure only temperature (with barometer as extra), SI7021 for temp/hum, BME280 for temp/hum more expensive but better.
• do not use voltage divider at all, you don't need one as you can just get Vcc from the A0 pin (with it I have some change of voltage related to temperature but not as wild as you seem to get. Maybe it's related to the DS18 measurement also ?)

With these changes and a si7021 breakout board from which I removed the voltage regulator (it's not consuming much, but without it is even better), I can send every minute, flash a led and I hardly see any drop in voltage after a few weeks of running.

[fleinze]

@Nca78 said:

add a capacitor of 100-200µF

I will try this, thanks! Currently I use the 10uF capacitor which is on the arduino pro minis on the raw pin side.

in your code, add a sleep command between message sending

How long do you sleep? In normal operation there is only one send command per loop, I only send battery level once every hour. I try to read vcc after sending the temperature so the battery is under some load when measuring.

use a better sensor that can accept a lower voltage

I already built one with a Si7021 sensor. But I ran out of CR2032 so I powered it using two AA cells. I should solder it back to coin cell now I got some.

you can just get Vcc from the A0 pin

I don't know this method do you have a link or can you explain it?

[fleinze]

@carmelo42 sorry I somehow missed your post. I use the standard-bootloader as I did not get Optiboot to run on the 3.3V/8MHz pro minis. I set the extended fuse to 0x07 (BOD disabled) by editing boards.txt.

[carleki]

@fleinze said:

@carmelo42 sorry I somehow missed your post. I use the standard-bootloader as I did not get Optiboot to run on the 3.3V/8MHz pro minis. I set the extended fuse to 0x07 (BOD disabled) by editing boards.txt.
thanks !

is is a bit confusing for me :

• we can burn the bootloader from the Arduino IDE : are the fuses written at this moment ?
• we can upload a sketch with the arduino IDE : are the fuses written at this moment ?
• with my researches, I found that for disabling BOD was possible with 0xFF value for efuse ?

I have some lifetime issues with my CR2032 sensor .. and I suspect the fuses are not correctly set ...

If you can light up my mind it will be perfect :)

[fleinze]

@carmelo42 The fuses only are written when you burn the bootloader, not when uploading the sketch. The Arduino IDE takes the fuse bytes from the boards.txt files.
It would also be possible to just set the fuse bytes by using the avrdude-program from a command line, but you will still need to use a programmer.
The extended-fuse setting 0xFF is the same as 0x07 as only the last 3 bits of this bytes are used. Both values will give you BOD disabled.

[fleinze]

I just added an 100uF capacitor to one of my sensors and put an old battery in. Let's see how much more life I can get out of this battery now.

[carleki]

@fleinze
Hi, do you think it's possible to connect de Dallas sensor to pin 7, 8 and 9 of the arduino ?

Like this :

#define ONE_WIRE_BUS 8 // Pin where dallase sensor is connected
#define ONE_WIRE_GND 9
#define ONE_WIRE_VCC 7

I have tried, and the temperature is always 85°C ...

[Nca78]

Hello @carmelo42, pin 9 is supposed to be connected to the NRF24 (CE / Chip Enable) so it cannot work as ground for the sensor as it will be high (and so = to Vcc) most if not all of the time.

[flopp]

@fleinze said:

I just added an 100uF capacitor to one of my sensors and put an old battery in. Let's see how much more life I can get out of this battery now.

Very interest work.
Is it still working?

[Moebius Lutching]

There is a TI paper about adding a big capacitor in series with the coin-cell battery to minimize the voltage drop during high-current peaks: http://www.ti.com/lit/wp/swra349/swra349.pdf, also another interesting article related to low-power and CR2032: http://www.low-powerdesign.com/121312-article-extending-battery-life.htm

[fleinze]

@flopp I added the capacitor and put the old battery in. By old battery I mean the one I had replaced a week earlier for a new one. Sensor running smooth since, so great success!