I've finished my project and now I'm measuring the current but there is something wrong. I'm using an Arduino Pro Mini board and the LowPower library but the consumption is about 3.5 - 5 mA and not less than 500 uA (the board remains into sleep mode almost all the time).

When I began to work with the board its LED was removed but I think that this work was not made correctly. How can I check that LED was removed correctly?

Thanks to all.

EDIT1: The strange power consumption is not associated with board's LED.

EDIT2: @Gerben has suggested me to review the state of SPI pins connected to the board. I use in this project a SD card module and GSM/GPRS module but the guilty of this excessive power consumption is the first. Then I've disconnected all SD card module's pins and then I get about 60 uA, so the problem is on those pins but I can't reduce the power consumption. SD card module pins are 10,11,12 and 13 so I've used statements like digitalWrite(10, LOW), digitalWrite(11, LOW) and so on after reading/writing on the SD card but it is useless.

EDIT3: I've decided to upload a representation of my project using Fritzing. The external modules are not identical but they contain the same pins.

General view of the circuit:general view of the circuit.

Detail of the connections:

more detail

I use these external components:

In my project there are some important details:

  • GPRS module is powered individually. The other battery is dedicated to power on the Arduino board and the SD card module.
  • Batteries are 6v.
  • Transistors base are controlled by 2 and 3 digital pins respectively.
  • The 8 and 9 pins of the Arduino board act like RX and TX pins using AltSofSerial.h library.
  • See Power saving techniques for microprocessors for some tips. I doubt it is anything to do with the non-existent LED.
    – Nick Gammon
    Feb 4, 2017 at 8:33
  • How would you remove an LED in such a way that the missing LED draws 5 mA? That doesn't make any sense. Either it is still there, or it is not there. If the removal shorted the pins then you would have a lot higher current drain than 5 mA.
    – Nick Gammon
    Feb 4, 2017 at 8:34
  • @NickGammon I think that the problem is the SD card module because if I disconnect the CS, DI, DO and CK pins then the consumption is around the 60 uA.
    – cpinamtz
    Feb 6, 2017 at 14:56
  • @PinaGamer did you just disconnect those pins or also the VCC and GND pins of the SD card module? If you didn't, try leavinf those pins connected: if it is a module it should have an onboard converter and maybe a level shifter which remain powered (if it is the case, power it through an arduino pin and turn it off when not needed). If you only disconnected those pins and left VCC and GND connected, see with an oscilloscope if the status is changing. If it isn't, try measuring also the current sinked by the SD card (module) when in sleep
    – frarugi87
    Feb 6, 2017 at 15:51
  • 2
    @PinaGamer because if you switch off the transistor, every node on the SD should float up to VCC, the only remaining connection. If you apply a 0V on any pin, you put a differential voltage over the board, thus turning on something. Try with a high value (so everything is at VCC) or put the pins in high impedance (aka input mode). A PMOS transistor (or a PNP) is used to interrupt the VCC pin instead of the GND one, so you can keep the grounds together (it's usually a better approach, since usually grounds are designed to be together)
    – frarugi87
    Feb 8, 2017 at 10:57

2 Answers 2



My problem was that the SD card module was consuming when it was controlled by a transistor and my Arduino board was into the sleep mode. So I wrote into the void setup() the digitalWrite(PIN, HIGH) statements where PIN represents all pins connected to the board that belong to the SD card module (DI, DO, CS, and CK pins), to enable the internal resistor of that pins. Then, I checked the power consumption and I reached less than 100 uA.


If you physically removed the LED make sure the pads for it aren't shorted together by old solder. If they aren't then you removed it correctly.

However: 5mA may be a perfectly reasonable current consumption for your project. Without seeing a full schematic and analysing your code it's impossible to say what kind of current you would expect to see.

  • I've upload a simple project like this: #include <LowPower.h> void setup(){ LowPower.powerDown(SLEEP_TIME, ADC_OFF, BOD_OFF); } void loop(){ } And the consumption is a bit less than 3.5 mA. So I think that the code is not the problem
    – cpinamtz
    Feb 3, 2017 at 12:00
  • Like what? Also, how are you powering the board?
    – Majenko
    Feb 3, 2017 at 12:03
  • I power the project using 4 AA batteries with 1900 mAh.
    – cpinamtz
    Feb 3, 2017 at 12:05
  • 1
    Interesting... I've isolated the board, I've measured again the current and now I'm getting 60 uA. So the problem is in the circuit... There are connected an SD card and GSM modules both controlled using transistors.
    – cpinamtz
    Feb 3, 2017 at 12:13
  • 2
    @PinaGamer If you remove power using a transistor, you must also make sure not the the SPI/UART pins are HIGH. Otherwise power will flow into the modules via this pin (and the clamping diodes in the modules ICs).
    – Gerben
    Feb 3, 2017 at 13:33

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