๐Ÿ’ฌ Battery Powered Sensors

  • Hi guys, if your Arduino is equipped with an ATMega 328P then it could go down to 1.8V at lower frequencies like 1MHz (8MHz internal RC oscillator / 8 by default).
    Or you can use the internal low power 128KHz RC osc eventually ...
    It means you could power both the Arduino and the radio directly from the battery string and consume even less current.
    Just wondering if anyone tried these cases so far?

  • Mod

    There have been some users that went that way but personally I am preferring to use a single AA LiFePo4 battery with standard voltages and clocks

  • I am a newbie and have some thoughts about the battery level that I did not find in this forum.
    The 8MHz 3.3V Arduino Pro Mini can handle down to roughly 2.8V.
    If I have understood the calculations in the sketch correctly then the analog value of A0 is 1023 at 3.44V and 0 at 0V.
    This means that at 2.8V the value is about 830 = 83% and under this, the Arduino stops working. Is this right?
    If this is correct, I wonder if someone has changed the calculation in the sketch so that the battery percentage becomes 0 at 2.8V?
    This would mean that the battery percentage becomes a more real value on the battery level.

  • Mod

    It's a simple percentage calculation that you can do it in the code

  • @gohan Thanks for your reply, you can show me how the code should look.

  • Mod

    void batM() //The battery calculations
      // Battery monitoring reading
      int sensorValue = analogRead(BATTERY_SENSE_PIN);
      // Calculate the battery in %
      float Vbat = sensorValue * VBAT_PER_BITS;
      send(msgVBat.set(Vbat, 3));
      int batteryPcnt = static_cast<int>(((Vbat - VMIN) / (VMAX - VMIN))*100.);
      Serial.print("Battery percent: "); Serial.print(batteryPcnt); Serial.println(" %");
      // Add it to array so we get an average of 3 (3x20min)
      batArray[batLoop] = batteryPcnt;
      if (batLoop > 2) {
        batteryPcnt = (batArray[0] + batArray[1] + batArray[2] + batArray[3]);
        batteryPcnt = batteryPcnt / 3;
        if (batteryPcnt > 100) {
          batteryPcnt = 100;
        Serial.print("Battery Average (Send): "); Serial.print(batteryPcnt); Serial.println(" %");
        batLoop = 0;

    This is the function I use, I just define the VMAX and VMIN in the beginning of sketch. The function calculates an average of 3 measurements before sending the value

  • Hardware Contributor

    @gohan said in ๐Ÿ’ฌ Battery Powered Sensors:
    Hello, i didn't know why you add 4 measures (batarray) and you divide by 3 the sum .

  • Mod

    @tonnerre33 good catch! maybe it's an optimistic value ๐Ÿ™‚

  • Mod

    I actually didn't look much at battery percentage, but I prefer looking at the voltage that gives me a better idea of how the battery is doing since I can log the values on a graph

  • @magnusf It is important to know that the battery voltage is non linear in respect to how much juice left. Just search for "battery discharge curve" to see how much it depends on battery type, current and temperature. So calculating the percentage is actually meaningless unless You exactly know how much current your board sucks at what temperature and what type of battery You use.

  • Instead of using "DC-DC Step Up Boost Module 5V" for a HBS, wouldnยดt it make sense to just use 2 AA batteries for the nano and 2 additional batteries (i.e. four in a row) for the HBS?

  • Mod

    What's the hbs?

  • Same as on the motion example - HC-SR501, 4.5V- 12V.

  • Maybe only a third Battery, as the HBS only needs 4.5V..

  • To answer my own question: yes, it seems to work. Searched around and read a while, found this:
    Best addition imho ,no need for step up / down. ๐Ÿ˜„

  • Hi,
    I'm trying to build a Soil Moisture sensor with NiMh battery and solar panel as in another post. I use a stepup converter to 3.3V connected on the VCC of a pro-mini 3.3V. The sensor seems working when connected to FTDI USB device, ut once I remove the power from FTDI, no more communication. I measured the voltage on the output of the stepup which indicates 3.26V. Is it norml or a defective step-up ? And should I remove the regulator of the pro-mini as suggested above or not ? (in article above, it states the regulator is not necessary, but it doesn't say if pro-mini would still work if regulator remains there).
    Thanks for your support

  • Mod

    @ricorico94 what does the debug output from the node and the gateway say?

    What regulator are you using? Most regulators produce power that is too noisy to be usable by the nrf24 radio (you didn't state which radio you're using so I'm just guessing here, based on the most common problems). What capacitor(s) are you using after the regulator?

    See https://forum.mysensors.org/topic/666/debug-faq-and-how-ask-for-help/ for the most common problems and how to diagnose them.

    Also see https://www.mysensors.org/build/battery for more information about battery powered sensors.

  • Hi,
    As regulator I use a stepup like that one:

    I use a NRF24L01 as radio module following the connection guidelines from Mysensors. I did not add any capacitor to 3.3 and ground of the NRF24L01.
    I connected the vO of the stepup to the VCC (the VCC between RX and GRD and not the RAW) of the arduino pro mini 3.3V as indicated in this post:https://forum.mysensors.org/topic/4045/solar-powered-soil-moisture-sensor
    I use indeed a similar lamp with its small NiMh battery (1.2v) and its solar panel.
    The NRF24L01 is connected on GRD (between RST and RAW) and on VCC (between A3 and RST). I hadn't put any capacitor.
    I tried following your advice to add a 0.1uF ceramic capcitor between VCC (the one between RX and GRD) of pro mini and its ground, but apparently, I face same issue.
    (I did not solder the capcitor yet, I only connected through the pins I usually use for the FTDI)

    26 TSM:INIT
    28 TSF:WUR:MS=0
    36 TSF:SID:OK,ID=4
    38 TSM:FPAR
    75 TSF:MSG:SEND,4-4-255-255,s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=OK:
    2086 TSM:FPAR
    2123 TSF:MSG:SEND,4-4-255-255,s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=OK:
    4132 TSM:FPAR
    4169 TSF:MSG:SEND,4-4-255-255,s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=OK:
    6178 TSM:FPAR
    6215 TSF:MSG:SEND,4-4-255-255,s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=OK:
    8222 !TSM:FPAR:FAIL
    8224 TSM:FAIL:CNT=1
    8226 TSM:FAIL:DIS
    8228 TSF:TDI:TSL
    18229 TSM:FAIL:RE-INIT
    18231 TSM:INIT
    18237 TSM:INIT:TSP OK
    18241 TSF:SID:OK,ID=4
    18243 TSM:FPAR
    18280 TSF:MSG:SEND,4-4-255-255,s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=OK:
    20289 !TSM:FPAR:NO REPLY
    20291 TSM:FPAR
    20328 TSF:MSG:SEND,4-4-255-255,s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=OK:
    22337 !TSM:FPAR:NO REPLY
    22339 TSM:FPAR
    22376 TSF:MSG:SEND,4-4-255-255,s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=OK:
    24385 !TSM:FPAR:NO REPLY
    24387 TSM:FPAR
    24424 TSF:MSG:SEND,4-4-255-255,s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=OK:
    26433 !TSM:FPAR:FAIL
    26435 TSM:FAIL:CNT=2
    26437 TSM:FAIL:DIS
    26439 TSF:TDI:TSL
    36442 TSM:FAIL:RE-INIT
    36444 TSM:INIT
    36450 TSM:INIT:TSP OK
    36454 TSF:SID:OK,ID=4
    36456 TSM:FPAR
    36493 TSF:MSG:SEND,4-4-255-255,s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=OK:
    38502 !TSM:FPAR:NO REPLY
    38504 TSM:FPAR
    38541 TSF:MSG:SEND,4-4-255-255,s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=OK:
    40550 !TSM:FPAR:NO REPLY
    40552 TSM:FPAR
    40589 TSF:MSG:SEND,4-4-255-255,s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=OK:
    42598 !TSM:FPAR:NO REPLY
    42600 TSM:FPAR
    42637 TSF:MSG:SEND,4-4-255-255,s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=OK:
    44646 !TSM:FPAR:FAIL
    44648 TSM:FAIL:CNT=3
    44650 TSM:FAIL:DIS
    44652 TSF:TDI:TSL
    54657 TSM:FAIL:RE-INIT
    54659 TSM:INIT
    54665 TSM:INIT:TSP OK
    54669 TSF:SID:OK,ID=4
    54671 TSM:FPAR
    54708 TSF:MSG:SEND,4-4-255-255,s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=OK:
    56717 !TSM:FPAR:NO REPLY
    56719 TSM:FPAR
    56756 TSF:MSG:SEND,4-4-255-255,s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=OK:
    57493 TSF:MSG:READ,0-0-4,s=255,c=3,t=8,pt=1,l=1,sg=0:0
    57499 TSF:MSG:FPAR OK,ID=0,D=1
    58765 TSM:FPAR:OK
    58767 TSM:ID
    58767 TSM:ID:OK
    58769 TSM:UPL
    58806 !TSF:MSG:SEND,4-4-0-0,s=255,c=3,t=24,pt=1,l=1,sg=0,ft=0,st=NACK:1
    60815 TSM:UPL
    60852 !TSF:MSG:SEND,4-4-0-0,s=255,c=3,t=24,pt=1,l=1,sg=0,ft=1,st=NACK:1
    62861 TSM:UPL
    62863 TSF:MSG:SEND,4-4-0-0,s=255,c=3,t=24,pt=1,l=1,sg=0,ft=2,st=OK:1
    64872 TSM:UPL
    64909 !TSF:MSG:SEND,4-4-0-0,s=255,c=3,t=24,pt=1,l=1,sg=0,ft=0,st=NACK:1
    66918 !TSM:UPL:FAIL
    66920 TSM:FPAR
    66957 TSF:MSG:SEND,4-4-255-255,s=255,c=3,t=7,pt=0,l=0,sg=0,ft=1,st=OK:
    68964 !TSM:FPAR:NO REPLY
    68966 TSM:FPAR
    69003 TSF:MSG:SEND,4-4-255-255,s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=OK:
    71012 !TSM:FPAR:NO REPLY
    71014 TSM:FPAR
    71051 TSF:MSG:SEND,4-4-255-255,s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=OK:
    73060 !TSM:FPAR:NO REPLY
    73062 TSM:FPAR
    73099 TSF:MSG:SEND,4-4-255-255,s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=OK:
    75108 !TSM:FPAR:FAIL
    75110 TSM:FAIL:CNT=4
    75112 TSM:FAIL:DIS
    75114 TSF:TDI:TSL

    Apparently, it sends correctly packets but can't receive any ACK or message from the gateway.
    I got this log by connecting a FTDI adapter with only the RX/TX cables. If ever I connect also the GRD and 3.3V of the FTDI, then I get no error message at all (even without the capacitor) and Domoticz receives all updates (and also sends as I use Domoticz to send customized sleep duration to the sensor).

    Should I try adding both the 0.1uF to VCC/GRD of arduino and also a 4.7uF to the 3.3/GRD of the NRF24 as suggested in the "Connect the Radio" page ?
    Any idea ?

  • Mod

    @ricorico94 yes add the recommended capacitor.
    Also check the gateway log at the same time you check the node log. That will let you know if the gateway isn't hearing the node, or if the node isn't hearing the gateway.

  • Thanks for the advice, I'll try that.
    For the log on the gateway side : I use a gateway on the raspberry pi itself (as per https://www.mysensors.org/build/raspberry ) of my Domoticz installation. Is there an easy way (like via telnet) to get the logs other than by creating the new line in the config file ? Maybe the 3rd option proposed with "mysgw.pipe" ? (in such case, do I need to reboot whole raspberry after modifying the config file?)

  • Mod

  • Thanks to another arduino forum, I found what was wrong.. probably indeed a stability of power due to step-up converter. In that forum, they were explaining that receiving is more sensitive to power noise than sending data and that in such case, it's good to add a 100uF capacitor on 3.3V and GRD of radio module. I tried 100uF and it worked.. I then tried with 47uF and it's still working. (I had tried with 0.47uF and it was not working at all)

    In the "Connect Radio" guidelines, of Mysensors, it is stated that a capacitor of 0,47-47uF is improving reliability but that "the exact size usually doesn't matter" which was misleading in my case.
    Could I suggest to rephrase that sentence into "the exact size usually doesn't matter, but you can try 47uF if 0.47uF still doesn't work, especially if sending data works well and not receiving data." ?

    Edit for Erratum: please read 4.7-47uF instead of 0,47uF-47uF. Tests I had made were with 4.7uF as well, not 0.47uF

  • Mod

    @ricorico94 great input, thanks! I have updated the page, except that I changed 0.47uF to 4.7uF in your text since the recommendation is 4.7 - 47)

  • oups, indeed. I'll edit my post as well to avoid confusion as well. Thank you for your support, I appreciated a lot.
    By the way, I could never find how to get the logs in my gateway installed on raspPI. But that's another post. ๐Ÿ˜‰

  • Hello together,

    I'm just trying to get the voltage measurement to work. But there is something wrong. I built everything as shown above and uploaded the program to the Arduino pro mini. The only thing I changed is the sensing Pin A0 -> A3
    In debug mode I see the following (the supply voltage is constant 3.3V):

    Battery Voltage: 3.12 V
    Battery percent: 92 %
    Battery Voltage: 2.40 V
    Battery percent: 71 %
    Battery Voltage: 2.32 V
    Battery percent: 69 %
    Battery Voltage: 2.31 V
    Battery percent: 68 %
    Battery Voltage: 2.29 V
    Battery percent: 68 %
    Battery Voltage: 2.30 V
    Battery percent: 68 %
    Battery Voltage: 2.33 V
    Battery percent: 69 %

    What could be the reason? That doesn't make sense to me.

  • @maschler You may be picking up noise which will give an unsteady voltage during the ADC sample.
    A 0.1uF electrolytic cap between the analogue pin and ground in parallel with the resistor should stabilise it sufficiently.
    I use this arrangement with much higher resistances which are known to increase noise, the capacitor maintains a steady voltage sufficient for the ADC sample period.
    One thing worth checking with a multimeter is what the actual voltage is on supply and on the pin. The 1.1v bandgap is sometimes not exactly 1.1v, particularly on clones. Once you know the two values you can modify the ratio and you should get reliable and accurate readings.

  • Mod

    The 1.1v reference could be + or - 10%, but a small ceramic cap on near the analog pin should help to stabilize the reading. Also taking 3 measures and then sending the average is a good way of minimizing errors

  • Plugin Developer

    I'm looking for a USB rechargeable battery that can deal with very low power drain, so that I can power an Arduino Nano. Most power packs will not work with very small currents - they turn themselves off. So ideally it should not be too clever..

    Does anybody have a favourite?

  • Mod

  • It would be great to add to this arctle that if you want to be battery powered outdoors with temperature below zero - you have to use lithium batteries (FR6 for AA) (yes, batteries, not li-ion accumulators!) (for example ultimate lithium energizer, also could be found lithium batteries from other vendors), because Alkaline (LR6 for AA) will be frozen and loose their capacity heavily. If i remember it is >50% at -10 C and death at -20 C. Same problem for li-ion accumulators - when liquid is frozen - electrons are stucked...
    Also would be great to add some link about battery/accumulator types, advanteges and disadvantages, but i have no links in english, easy-to-read and in one place...

    But i have very great link about battery-powering that really should be added here, but in advanced section:

  • @nekitoss Not sure where you got your information but my Gas Node is on it's second year running on the same two Varta AA alkalines and been down to -20 on more than a few occasions last winter, typically 4 months below -10... Currently the temperature is -3 and headed to -8 overnight, voltage is 2.98, will probably need to replace them in autumn 2019...

  • The tap point could be bypassed with a 0.1 uF capacitor

    Can someone explain, how exactly I should connect this capacitor? Should it be between A0 and GND? Would be great to see this capacitor in the graphic.

  • @benhub That rather depends what you are quoting from, as could not find the original statement.
    If it is to do with stabilising voltage from a point on a resistor divider to read it on the analogue pin, the capacitor is from the analogue pin to ground.
    It's purpose to dampen oscillations long enough for the ADC to sample the voltage, but usually only where high value resistances are used.

  • The quote is from this sample : Measuring and Reporting Battery Level

    Use a 1Mโ„ฆ (R1) and 470Kโ„ฆ (R2) resistor in series, connected to the positive terminal on the battery and ground and then connected the tap point to the A0 input on the CPU.

    The tap point could be bypassed with a 0.1 uF capacitor to keep the noise level low, at this otherwise high impedance point.

  • @tonbor Yes, the capacitor goes from the analog input to ground.

  • Mod

    @skywatch @tonbor @benhub @zboblamont thanks for your input. I have updated the page. I added the text in bold:

    The tap point could be bypassed with a 0.1 uF capacitor (connected in parallel with R2) to keep the noise level low

    and updated the image. Please let me know if something is still unclear.

  • Perfect!

  • If you remove the regulator and power with 2xAA batteries, do you only need the TX and RX pins for the FTDI programmer and if so can you use the RX and TX pins on the left side instead of the top FTDI pin connector? Trying to think how to connect the FTDI programmer without connecting to it's VCC and ground when there is no regulator on the pro mini.

  • Mod

    @macgyver33 you need rx, tx and gnd.

    The pins on the left side and the ones on the top work the same way, you can use the ones on the left if you prefer.

  • Is exist something "last wish" in MySensors, when battery go below predefined level the device to send last massage to the GW and go sleep forever.
    The idea is the controller/application to have information about the device and to be known this device is dead and need battery change.

  • Mod

    @tiana the controller will know the last battery level. Just set the predefined level in your controller?

  • Yes but in this case the last massage will be the same like the previous, only the battery level will be below some predefined value. i don't like this. I will think how to solve this.

  • @tiana - Of course you can do this in your code.

    Just read the battery level and when it gets to the lowest level you decide upon (maybe a little testing needed here) then include the line...

    if(battery_level_read < battery_low_level){
    send.msg(your last message)
    sleep(long time period)

    You need to define all the things above as normal for variables (floats for the battery reading and levels and UL for the long sleep)....

  • @tiana I agree with @mfalkvidd , normally it is the Controller which sends out the warning to change battery, certainly Domoticz has this provision incorporated?
    Here the batteries are read at approximate 12 hour intervals, and Domoticz is preset to signal a warning below 1.7v, which is days or even weeks from actually dying. If I'm away or forgetful it will cease updating anyway and flag Red on the display.
    Once you have established the consumption curve for your batteries until flat, easy enough to set the warning threshhold before the Node dies...

  • @tiana
    Create dummy contact sensor on your node and if node sends last message, it will trigger this contact before "die".
    So controller knows, that it was last message and node is off.
    But better is allow controller do its job, like wrote all others.
    I personally check battery level and "no incoming messages in supposed interval" to send alert to my e-mail ( and SMS ).
    In this example tank level sensors sends every 10min, so after 3 messages lost, I will be informed.


  • Thanks for the ideas, i will modify the code to use LowPower lib and will cut the power to the radio module to increase battery live, when last massage is send the node will never power the radio module, will be only short interrupt and go again to sleep forever. This will give me power usage 20times more than self battery discharge. Which have to give me node uptime around 260days with coin cell battery.

  • @tiana
    And for what will be that offline node usefull?

  • Door/Window/Button

  • @tiana
    Forever sleeping door sensor with low battery?

    "when last massage is send the node will never power the radio module"

    Why door sensor, if it never sends message?

  • @kimot
    At all of the time 328p will be in sleep forever, when button is pressed interrupt is triggered and wake the 328p power ON the radio send info power OFF radio and go sleep forever.
    Only when battery level go below critical level. the radio stay OFF and only interrupt and sleep forever.

    I am almost ready with the drawings of the hardware, and next week start work on software... you can see the project in the openhardware.io i gonna upload it later tomorrow.

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