[TIPS] battery powered sensors

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In this topic I want to place all kinds of battery tips like how to reduce power consumption and how to measure your battery life for instance. I’m not a expert on this, but i want to share all the things i found out.

This topic will be based on Arduino Pro Mini’s (3.3V) and Attiny’s.

Hardware mods

The 3.3V pro mini is a easy to use device. It has all the functions you need and its quite small. If you want to use it for a battery powered sensor you must do some modifications because it draws to much power by itself.

Remove the power LED and regulator

The LED uses around 1,5 mA, thats quite a lot. The regulator uses around 50uA. Sounds not that much but imagine that a PIR sensor uses around 240 uA with the regulator. Remove the components according to the image below (please do not cut any lines, removing the components will do it). After that you can’t use the Vcc of the programmer anymore.

Software mods

Change BOD to 1.8V instead of 2.7V

This step is a little bit harder. because you have do change some fuses in the 328P (this is not needed for the attiny’s because the drop-out voltage is disabled by default). By default the Arduino has a drop-out voltage of 2.7V. That means if your batteries are lower than 2.7V, the Arduino stops working. You can adjust it to 1.8V or even disable it. The main thing what its all about is that you have the fuses like this:

LOW: 0xff
HIGH: 0xda
EXTENDED: 0x06

Go to your arduino folder.

Mac: user/library/arduino15/packages/arduino/hardware/avr/1.6.x/
Windows: [arduino folder]\hardware\arduino\

open boards.txt and search for ## Arduino Pro or Pro Mini (3.3V, 8 MHz) w/ ATmega328

a little bit lower your see this:

pro.menu.cpu.8MHzatmega328.bootloader.low_fuses=0xFF
pro.menu.cpu.8MHzatmega328.bootloader.high_fuses=0xDA
pro.menu.cpu.8MHzatmega328.bootloader.extended_fuses=0x05

change it to:

pro.menu.cpu.8MHzatmega328.bootloader.low_fuses=0xFF
pro.menu.cpu.8MHzatmega328.bootloader.high_fuses=0xDA
pro.menu.cpu.8MHzatmega328.bootloader.extended_fuses=0x06

Now all you have to do is re-burn the bootloader with a AVRISP or an arduino as ISP (read here below).

Run the Pro Mini on 1 Mhz

If your arduino is running on 8 Mhz, it can’t go lower than 2.4V. If you change it to 1 Mhz, it can go to 1.8V. To do this you need a custom board and a new bootloader for the arduino IDE.

Go to your arduino folder and edit the boards.txt.

Mac: user/library/arduino15/packages/arduino/hardware/avr/1.6.x/
Windows: [arduino folder]\hardware\arduino\

search for ## Arduino Pro or Pro Mini (3.3V, 8 MHz) w/ ATmega328 and add this after the last line (pro.menu.cpu.8MHzatmega328.build.f_cpu=8000000L) of this device:

## Arduino Pro or Pro Mini (1.8V, 1 MHz) w/ ATmega328
## --------------------------------------------------
pro.menu.cpu.1MHzatmega328=ATmega328 (1.8V, 1 MHz)

pro.menu.cpu.1MHzatmega328.upload.maximum_size=30720
pro.menu.cpu.1MHzatmega328.upload.maximum_data_size=2048
pro.menu.cpu.1MHzatmega328.upload.speed=9600

pro.menu.cpu.1MHzatmega328.bootloader.low_fuses=0x62
pro.menu.cpu.1MHzatmega328.bootloader.high_fuses=0xD4
pro.menu.cpu.1MHzatmega328.bootloader.extended_fuses=0x06
pro.menu.cpu.1MHzatmega328.bootloader.file=atmega/ATmegaBOOT_168_atmega328_pro_1MHz.hex

pro.menu.cpu.1MHzatmega328.build.mcu=atmega328p
pro.menu.cpu.1MHzatmega328.build.f_cpu=1000000L

The next thing you have to do is add a new bootloader. In the arduino folder go to bootloaders/atmega/ and create a new hex file called ATmegaBOOT_168_atmega328_pro_1MHz.hex

In this file add these hex codes and save it:

:107E0000112484B714BE81FFE6D085E08093810001
:107E100082E08093C00088E18093C10086E0809377
:107E2000C2008CE08093C4008EE0BFD0259A86E02B
:107E300023EC3FEF91E0309385002093840096BBC4
:107E4000B09BFECF1D9AA8958150A9F7EE24FF2480
:107E5000AA24A394B5E0CB2EA1E1BA2EF3E0DF2E45
:107E600098D0813461F495D0082FA5D0023829F13B
:107E7000013811F485E001C083E083D07FC08234F3
:107E800011F484E103C0853419F485E09CD076C0F8
:107E9000853579F47ED0E82EFF247BD0082F10E0C2
:107EA000102F00270E291F29000F111F84D07801E1
:107EB00065C0863521F484E086D080E0DECF84364C
:107EC00009F040C066D065D0082F63D080E0E81686
:107ED00080E7F80618F4F701D7BEE895C0E0D1E0D6
:107EE00058D089930C17E1F7F0E0EF16F0E7FF06A2
:107EF00018F0F701D7BEE8955ED007B600FCFDCFBD
:107F0000A701A0E0B1E02C9130E011968C9111977F
:107F100090E0982F8827822B932B1296FA010C0160
:107F2000A7BEE89511244E5F5F4FF1E0A038BF0770
:107F300051F7F701C7BEE89507B600FCFDCFB7BE05
:107F4000E8951CC0843761F424D023D0082F21D0B9
:107F500032D0F70185917F0114D00150D1F70EC0C6
:107F6000853739F428D08EE10CD085E90AD08FE02E
:107F700084CF813511F488E018D01DD080E101D084
:107F80006FCF982F8091C00085FFFCCF9093C600E3
:107F900008958091C00087FFFCCF8091C00084FDD0
:107FA00001C0A8958091C6000895E0E6F0E098E150
:107FB000908380830895EDDF803219F088E0F5DF4B
:107FC000FFCF84E1DECF1F93182FE3DF1150E9F7D5
:107FD000F2DF1F910895282E80E0E7DFEE27FF27CC
:027FE000099402
:027FFE0000057C
:0400000300007E007B
:00000001FF

Start up the arduino IDE and select board arduino pro mini and after that processor: Atmega328 (1.8V, 1 MHz).

Now you can burn your new bootloader with 1 Mhz with a AVRISP or arduinoISP.

The arduino programmer (ISP)

To change the fuses, you need an AVR programmer. The easiest way is to use a Arduino Uno and load the sketch ‘ArduinoISP’ to it. after that set it up like this:

In the programs AVRFuses or AVR studio you can simply use the AVRISP programmer.

Measure your battery

If you attach your batteries directly to the Vcc, the 328p or attiny can measure the voltage. This can be used as battery level (Be aware: this gives you an indication, its not 100% accurate).

Add this to the bottom of your sensor sketch in the Arduino IDE (or add this library):

long readVcc() {
  // Read 1.1V reference against AVcc
  // set the reference to Vcc and the measurement to the internal 1.1V reference
  #if defined(__AVR_ATmega32U4__) || defined(__AVR_ATmega1280__) || defined(__AVR_ATmega2560__)
    ADMUX = _BV(REFS0) | _BV(MUX4) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1);
  #elif defined (__AVR_ATtiny24__) || defined(__AVR_ATtiny44__) || defined(__AVR_ATtiny84__)
    ADMUX = _BV(MUX5) | _BV(MUX0);
  #elif defined (__AVR_ATtiny25__) || defined(__AVR_ATtiny45__) || defined(__AVR_ATtiny85__)
    ADMUX = _BV(MUX3) | _BV(MUX2);
  #else
    ADMUX = _BV(REFS0) | _BV(MUX3) | _BV(MUX2) | _BV(MUX1);
  #endif  
 
  delay(2); // Wait for Vref to settle
  ADCSRA |= _BV(ADSC); // Start conversion
  while (bit_is_set(ADCSRA,ADSC)); // measuring
 
  uint8_t low  = ADCL; // must read ADCL first - it then locks ADCH  
  uint8_t high = ADCH; // unlocks both
 
  long result = (high<<8) | low;
 
  result = 1125300L / result; // Calculate Vcc (in mV); 1125300 = 1.1*1023*1000
  return result; // Vcc in millivolts
}

Now you can call the function readVcc():

float batteryV = readVcc();

To change it to percentages you have to set the minimal voltage (empty) and the max voltage (full).

Lets say 3.2V is full and 2.4V is empty.

then this is the formula:

int MIN_V = 2400;
int MAX_V = 3200;
batteryPcnt = min(map(batteryV, MIN_V, MAX_V, 0, 100), 100);

So if your battery is 2.8V: (((2800 - 2400) / (3200 - 2400)) * 100 ) = 50%

more to be add…

If you have any tips, feel free to post it!

@sweebee very interesting thanks for sharing!

@Yves911 thanks!

The next thing is running the pro mini on 1 Mhz instead of 8 Mhz. With 8 Mhz the arduino can go to 2.4V. With 1 Mhz it can go to 1.8V.

I have to create a new bootloader (hex file) for this, but i’m getting compile errors. So if anyone has already done it?

From my understanding, and my experiences so far, is that if you remove voltage regulator, you can use vRaw not VCC. Suppose you have input greater than 3.3v or 5v (depend from your model) , input from vRaw is processed by voltage regulator then it gives output to Vcc. Therefore if you remove the voltage regulator, you cannot put the input for vRaw.

Please refer to arduino pro mini data sheet for this.

Other tips

• use arduino pro mini 8MHz 3.3v combine with nrf24l01+ radio. While sleep, it only consume 40uA

• removing voltage regulator won’t gives you significant impact

• other way to reduce power consumption is try to downgrade uC speed by using internal oscillator. This method require bootloader modification and custom fuse

@funky81 in my opinion removing the regulator is worth it. Brought my pir node from 250uA to 150uA. And my dht22 node from 50 uA to almost nothing in sleep.

When the regulator is removed you cant use the vcc from the serial header and RAW is also unavailable.

Have you already done it? Changing the bootloader. I want to change it to 1 Mhz. Do you have a compiled hex one?

I can recommend this page for all possible power-saving functions of the arduinos:
http://gammon.com.au/power

Hi @sweebee, sorry for my late response.

@sweebee said:

@funky81 in my opinion removing the regulator is worth it. Brought my pir node from 250uA to 150uA. And my dht22 node from 50 uA to almost nothing in sleep.

Well depends on your case actually, please calculate everything include the risk that you will destroy the arduino in my case, bette to skip this step

When the regulator is removed you cant use the vcc from the serial header and RAW is also unavailable.

After check your picture…yes, you’re right.
You can’t use VCC from serial header.
my bad…

Have you already done it? Changing the bootloader. I want to change it to 1 Mhz. Do you have a compiled hex one?

Yup, I’ve done it, but do to several reason I change it back to 8MHz instead of 1MHz
I take the bootloader from this page

@funky81 Thanks, got it working

[update] Added a easier way to change the BOD fuse and how to change the arduino to 1 MHz.

I don’t know the folder to the boards.txt on windows.

@sweebee very very cool. i will test it with windows and give feedback!

@sweebee said:

I don’t know the folder to the boards.txt on windows.

It’s on [arduino folder]\hardware\arduino\boards.txt

@sweebee how much uA your consumption now?

@funky81 i dont know. Havent changed the clock On my sensors that are in use right now. Just tried it with a loose arduino. But i dont think it Will change a lot because the arduino is in sleep the most of the time. The only great thing of the lower clock is that it can run from 1.8v instead of 2.4v

Still waiting for more pirs to arrive from China and have to test how low they can go. I dont want to test On my sensors that are in use right now.

Arduino 1.8v
Nrf24 1.9v
Pir

@sweebee you should gives pir direct connection to battery or voltage regulator.

@funky81 Yes i bypassed the regulator On the pir. The lowest voltage i tried On the pir was 2.6V and that worked fine. Lets find out low low it can go.

Also tried a dht22, but its bounching up and down under 3V. So had to add a step-up converter for the dht only.

@sweebee yes, you can do that.

i have no board.txt in my IDE…

there is only a “tools” folder in this path: \Arduino\hardware\tools

@n3ro Well i don’t know on windows. But on my mac i have 2 folders. one in my documents but there is also no boards.txt. On mac there is a second folder hidden in the library from the computer.

Maybe there something similar on windows?

have a look here :

or search for boards.txt
shouldn’t be that hard to find - or you can try to use another ide version