Battery Life of Uno when not running a sketch

Has anyone tested the battery life of an alkaline 9 volt battery powering the Uno in a ready state but not actually running a sketch?

What I envision for my project is a reset button that executes the code for a period of time (say 30 minutes) to poll a barometric sensor. After the 30 minutes has ended, I want the Uno to 'turn off' or go into a sleep more until and external reset button is pushed. During the 'sleep time', how much is the current draw and or what is the anticipated battery life?

I understand the power regulator on the Uno consumes a few Ma but if someone has figured this out already I would appreciate the help.

Thanks!

A multimeter should answer that question fairly quickly.

Those little PP3 9V batteries are a hideously expensive way of providing power, and to add insult to injury the 5V regulator will throw away almost as much power as the UNO uses.

The chip itself uses microamps when sleeping but I remember reading that the voltage regulator and USB drivers both use a lot of current so even asleep your UNO would kill the battery quite quickly. There are various low power Arduinos that are designed to minimise power consumption and there are power management libraries that will take of powering down the on-chip devices for you. But none of this will do much good if you're using an UNO since the chip itself isn't the main problem.

If you really need to use a UNO, perhaps you could put a transistor in the power supply and have the UNO actually disconnect the battery when it's done?

I measured 11.4mA for an ATmega328P on a breadboard running an empty sketch. In power down sleep mode, it draws so little current that for all practical purposes, it can be considered to be zero.

I measured 42mA for an Uno running the same empty sketch. In power down mode, it measured 31mA. Not only is the Uno's voltage regulator still drawing current, so are other components on the board, including the ATmega8U2 MCU.

Looking at the specs for a Rayovac 9V alkaline no. A1604, I wouldn't expect more than about 12 hours life, and that's keeping the MCU in power down mode most of the time, and not running any other devices. Could be as short as 3 or 4 hours.

This is why there's aren't a lot of fans of the 9V rectangular batteries on this forum.

Just curious, what sort of sensor takes 30 minutes to poll?

Don't use an Uno, build your own custom board. Don't use a 9V cell, use 4x AA batteries. Lasts longer.

I've had reasonable success with an Arduino Fio sleeping, powered from a 2000mAh LiPo battery. I have it sleeping for 10 minutes and running for a few seconds when it wakes up (does a sensor reading, sends the reading out via an XBee). It runs for a couple of months between charges.

KirAsh4: Don't use an Uno, build your own custom board. Don't use a 9V cell, use 4x AA batteries. Lasts longer.

Agree, much better approach. @KirAsh4, have you used 4xAA? What do you use to get it down to 5V?

UNO is not designed to be low power with the components used in it check Olimexino-328 uses real low power LDOs and can consume as low as few micro-ampers in power down when powered with the li-po battery, the schematic also have build-in automatic battery charger

Based on everyone's response I now understand that the Uno is a pretty good development board and a way to program the chip. But for a device that I want to use in the field, the better solution will be to use the chip alone in my circuit with a set of AA batteries and perhaps a different voltage regulator. Thanks for all the great ideas.

[quote author=Jack Christensen link=topic=90194.msg677405#msg677405 date=1328311012] Just curious, what sort of sensor takes 30 minutes to poll? [/quote]

The project is interesting. I fly a plane with a ballistic parachute built into it. This device is only effective at an altitude of 400 to 500 feet above the ground.

What I want to create is a device that will let me know that I have reached 500 feet during my flight (but I only need the information once per flight). That way, if I have an engine issue during takeoff, I will know at what point the parachute is viable without having to do a mental calculation looking at the altimeter.

The idea is as follows -

Prior to takeoff, I go through a checklist of about 20 items. One of the items will be to push a momentary button (think reset) on a small box with the controller chip attached to a barometric sensor.

The sensor will detect the current atmospheric pressure on the ground.

Since I should be taking off within 30 minutes, the routine will be set to loop for that time frame.

At the moment the barometric sensor sees a drop in pressure equal to about 500 feet, I want the program to send a signal to an LED or a buzzer letting me know that I have reached 500 feet.

Once the program has done this one time or after 30 minutes has elapsed, I want it to power itself down and wait until the reset button is pushed again.

This is my first arduino project. (well the second, I did get the LED on the board to blink ;-)

Two questions: I assume this aircraft has electrical power - can you use that instead of AAs? Also, I'd assume that you'd like to know the viability of the parachute on approach too - why do you only want it on climb out?

mwrich: Based on everyone's response I now understand that the Uno is a pretty good development board and a way to program the chip. But for a device that I want to use in the field, the better solution will be to use the chip alone in my circuit with a set of AA batteries and perhaps a different voltage regulator.

Exactly. 2xAA or 3xAA with no VR can be a good way to go as well.

I assume this is an ultralight or similar with no convenient source of power, hence the need for a battery. Given the important nature of the cargo (i.e. you) I'd be giving a lot of thought to failure modes and human interface issues. For starters, when the button is pressed, how do we know the device is on and working? How do we know the battery is good? LEDs might be hard to see in direct sun, buzzers might be hard to hear over the engine.

Interesting project indeed! Good luck, have fun, and make sure the number of landings equals the number of takeoffs.

Can’t you look outside and see how high you are? I’m a pilot as well, and estimating altitude in the 400-500 ft range isn’t hard.

I think that I would try really hard not to use batteries for this project unless they wer rechargable type for use as backup power.

There would be few things more annoying than doing the check 30 minutes before take off, and then have the battery go flat at 499 feet and then you have engine failure. It could cancel your entire day.

I am interested to know what sort of output or alarm signal the propsed sensors provide. If they give you a simple onen/close contact then you caould probably do this without an Arduino at all.

It is always hard to help someone's project out when you are not facing, a). the problem and b). the external components.

[quote author=Jack Christensen link=topic=90194.msg677621#msg677621 date=1328330818] Agree, much better approach. @KirAsh4, have you used 4xAA? What do you use to get it down to 5V? [/quote]

I used MIC5205s to drop the voltage. The problem I had was that part of the project needed to be powered at a higher voltage than the uC, so I split Vin, one leg going to half the circuit, and the other leg to the MIC5205 and on to the uC.

Ultimately, during one of my more lucid moments, I realized that I could've added one small component to the one part of the circuit that needed the higher voltage, and actually change its characteristics to where it could've run at the same voltage as the uC. Then I could've used 3x AAs, no regulator and everything would've been just fine. Unfortunately, by then it was too late, the PCBs were already done, and the project was 2 days from completion and use.

Oh well, live and learn.

mwrich: if I have an engine issue during takeoff, I will know at what point the parachute is viable without having to do a mental calculation looking at the altimeter.

I'm struggling to think of any way an experienced pilot would deal with an engine failure that doesn't involve them knowing what altitude they're at. Don't you run through the other options before you decide to deploy the chute? I don't see how you can consider the other options without knowing your altitude.

Do you have a proper altimeter? How hard would it be to put a red marker on it to show your minimum safe recovery height?

KirAsh4:

[quote author=Jack Christensen link=topic=90194.msg677621#msg677621 date=1328330818]
Agree, much better approach. @KirAsh4, have you used 4xAA? What do you use to get it down to 5V?

I used MIC5205s to drop the voltage. The problem I had was that part of the project needed to be powered at a higher voltage than the uC, so I split Vin, one leg going to half the circuit, and the other leg to the MIC5205 and on to the uC.

Ultimately, during one of my more lucid moments, I realized that I could’ve added one small component to the one part of the circuit that needed the higher voltage, and actually change its characteristics to where it could’ve run at the same voltage as the uC. Then I could’ve used 3x AAs, no regulator and everything would’ve been just fine. Unfortunately, by then it was too late, the PCBs were already done, and the project was 2 days from completion and use.

Oh well, live and learn.
[/quote]

Thanks, that looks like a great regulator for the purpose. You’re in good company, I’m going through a slightly similar situation with one of my projects now.

PeterH:

mwrich:
if I have an engine issue during takeoff, I will know at what point the parachute is viable without having to do a mental calculation looking at the altimeter.

I’m struggling to think of any way an experienced pilot would deal with an engine failure that doesn’t involve them knowing what altitude they’re at. Don’t you run through the other options before you decide to deploy the chute? I don’t see how you can consider the other options without knowing your altitude.

Do you have a proper altimeter? How hard would it be to put a red marker on it to show your minimum safe recovery height?

The aircraft does has an altimeter. It is displayed as a tape on PFD (Primary Flight Display). No way to put a red marker on it like the altimeter you are think about.

The problem with an engine out issue at low altitude on takeoff is that you have very little time to make a decision. You basically have to have made your decision as to what you are going to do before you push the throttle forward while still on the ground. If the engine goes to deafening silence in a climb, the first thing you have to do is push the nose over to avoid a stall. Then quickly confirm the fuel pump is on boost, switch the fuel tanks and push the mixture full rich. If the engine doesn’t roar back to life from these actions then you either land straight ahead or if you are high enough, pull the chute. If you are above 1200 feet or so, you may be able to return to the airport.

My decision is to pull the chute if I am above 500 feet. And that is what I want to build the device for - to let me know I am at 500 feet.

rederikus: I think that I would try really hard not to use batteries for this project unless they wer rechargable type for use as backup power.

There would be few things more annoying than doing the check 30 minutes before take off, and then have the battery go flat at 499 feet and then you have engine failure. It could cancel your entire day.

I am interested to know what sort of output or alarm signal the propsed sensors provide. If they give you a simple onen/close contact then you caould probably do this without an Arduino at all.

It is always hard to help someone's project out when you are not facing, a). the problem and b). the external components.

I have 24 volt ship power available. I also plan to use a voice record module to record my voice and have it playback when I hit 500 feet. Basically I will say something along the lines of - "Caps viable, check flaps and Emax" (confirm flaps up and emax is a reminder to set the exhaust gas sensors to a baseline so I can lean the engine as I climb). The sound will come through my headset.

Can I source a voltage regulator that will allow me to use the ships power (24 volts)?

wildbill: Two questions: I assume this aircraft has electrical power - can you use that instead of AAs? Also, I'd assume that you'd like to know the viability of the parachute on approach too - why do you only want it on climb out?

On descent a nice little voice tells me when I am at 500 feet. It just doesn't do it when I am going up.

mwrich: Can I source a voltage regulator that will allow me to use the ships power (24 volts)?

They are readily available.