Can I save power like this?

Using Arduino Project Guidance
#1

So, I am a beginner with arduino. I am working on a little project, I have my Arduino, few sensors, few AD convertors, a display and an SD card datalogger. I need this thing to be battery powered and to log data only like every 5-10 minutes. And it needs to last on a battery for at least 24 hours. I was thinking about powering all the other boards through a MOSFET, that would turn them on only for a short time every 5-10 minutes, just to log the data and then turn them off again. Will this work? Or is there a better way to do something like this?

#2

Use a bigger battery?

#3

Yeah, but I figured that my whole circuit is drawing like 100 mA, while the Arduino itself takes only 20 mA, so if I could increase my battery life 4-5 times, that would be great.

#4

arduino sleep library.

http://playground.arduino.cc/Learning/ArduinoSleepCode

#5

But that will only put the Arduino in sleep, is that correct? But what about the other modules? They draw most of the power.

#6

Oh I see.

Well, what modules? Some have quiescent currents of nano amps...some may use mAs.

A more detailed outline of your system may help.

#7

What's using all the power?

Though an Arduino board typically uses about 50mA - they're not designed for low power - they've got two chips instead of one (and you can't sleep the 16u2), and a power light, and a crap regulator.

#8

So I am using a pro micro, MPX10dp pressure sensor paired with HX711 AD converter, micro SD card reader with real time module (labled as deek-robot) and a 2 line display with l2c driver.

#9

I use my arduino's mainly for animatronics.
I often use a traco DC/DC power convertor. It saves me a lot of battery power. Also the batteries I use are 7.2 volts so all my external boards are fed from the traco, NOT from the arduino. This way I can put the boards to sleep when I do not need them by turning them of with a mosfet.

I never needed to put the arduino to sleep with a decent battery. Some of my installations last more than 24 hours without a recharge...

Hope this helps.

#10

Great, thanks. I was thinking about using a 7,4 V lipol and some kind of a regulator, the arduino itself cannot power all the boards that I connect to it. So turing the other boards of with a mosfet is ok? Will they work properly with the arduino after being turned back on?

#11

Any particular reason you are using lipos for this ?

#12

Screpheep:
Great, thanks. I was thinking about using a 7,4 V lipol and some kind of a regulator, the arduino itself cannot power all the boards that I connect to it. So turing the other boards of with a mosfet is ok? Will they work properly with the arduino after being turned back on?

Yet again...these "other boards" are very elusive.

#13

I want to use a lipo because I have a few of them already at home. Is there a better alternative? The "boards" are the same ones as in my previous post, I should have written modules...

#14

Right.

Well those modules will be using essentially nothing.

So I am using a pro micro, MPX10dp pressure sensor paired with HX711 AD converter, micro SD card reader with real time module (labled as deek-robot) and a 2 line display with l2c driver.

The Pressure Sensor (MPX*) uses 6mA.
http://www.nxp.com/files/sensors/doc/data_sheet/MPX10.pdf

The HX711* uses 1.5mA while operational and less than a microamp when "sleeping" (not in use).

The real time clock will use nothing...they usually have a 100mA battery that lasts years.

Your main power suckers are that LCD screen (ranging 100mA+ I bet) and the arduino.

The arduino can go sleep. Have a transistor power off the LCD when not in use.

#15

Screpheep:
I want to use a lipo because I have a few of them already at home. Is there a better alternative? The "boards"

Good answer, i would suggest LA are better bang per buck and safer but if you already have them its difficult to beat 'free'.

#16

While not pertinent to the uno , i have used single cell lipos to power atmel based circuits without a regulator quite successfully. Only up to 8 MHz though.

Being single cell they are easy to charge/use with solar backup.

#17

I made some progress, I made a simple transistor switch to turn on and off the display. Connected the gate to digital pin 8. Tried just this simple code:

#include <Wire.h>
#include <LiquidCrystal_I2C.h>
int value = 0;
LiquidCrystal_I2C lcd(0x27, 16, 2);
void setup()
{
pinMode(8, OUTPUT); 
lcd.begin();
}

void loop()
{
 digitalWrite(8, LOW); 
 delay(2000);  
 digitalWrite(8, HIGH); 
 delay(500);  
 lcd.clear();
 lcd.print("Value: ");
 lcd.print(value);
 value++;
 delay(2000);
}

And this code does not work. The display turns on and initializes, but then it goes dark and never comes back. If I remove this part of the code:

 lcd.clear();
lcd.print("Value: ");
lcd.print(value);

The display turns on and off in the specified intervals, as it should. What am I doing wrong?

#18

Ok, I am an idiot :slight_smile: I am using a PNP transistor, so the display is on when pin 8 is LOW, not HIGH. Now it works.

#19