Sleep mode / Cut Power with RTC-Timer

Hi,

i’m working on a bachelor-thesis project with an arduino and want to power it with an akku-pack.

I use a normal Duemilanove with the ethernet shield and want to send the arduino to sleep and wake it up every minute or so to save power.
Using an adapter or Power-over-Ethernet is out of the question, sadly.

If I understood correctly, the arduino won’t save much power in sleep mode anyway since the regulator consumes power etc. And adding the ethernet shield will not make it any better.

What is the simplest way to completely cut power to arduino and wake it up via a timer? (And put it to sleep from with the arduino program).

I don’t want to get rid of the arduino and use only the avr-chip itself, since this would make the connection to the ethernet shield a new problem.

fabian

The simplest way would actually be to use the plain chip. The ethernet shield will do no good either.

What exactly would be your power budget / you admissible average current consumption? Depending on this number one can see how tight your constraints actually are.

Udo

I need the ethernet.

Rough calculated the circuit need ~300mA in Standby with seldom short peaks (<50ms) of 1500mA.

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What got me was:-

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@fab1an: I inquired how much current you want it to consume. If you really allow for 300mA average, then this absolutely no big deal.

Udo

@udo

I'm afraid I don't get your question. It is an Arduino+Ethernet-Shield, from the Internet I found, that that will consumer about 250-350 mA. A bistable display is connected to it, which needs 1500 during update.

I made another post in the Sparkfun forums which are connected to this topic: http://forum.sparkfun.com/viewtopic.php?f=14&t=22796 (I'm thinking of completely cutting off power)

fabian

@fab1an:

If I get you right your circuit currently consumes “to much” power. I am asking what exactly is “to much” and what exactly would be “acceptable”. That is:

  1. How much does your circuit consume currently under which exact conditions?
  2. How much capacity has the biggest acceptable battery?
  3. How much capacity are you aiming at?
  4. How much runtime are you aiming at.

(3) and (4) define your “power budget”. (1) tells how far you are away.

Example for (1) and (2): current consumption today: 200mA, biggest acceptable battery: 2000mAh @ 3V → Runtime 10h @ 3V

Example for (3) and (4): target capacity 2000mAh @ 3V, desired runtime 4 weeks = 28*24h → admissible average power consumption 2.97mA.

It follows that for 1s @200mA the device must sleep 67s @ <28 uA in order to stay within budget.

What I am asking for is the numbers. That is for the quantitative definition of “to much” and "acceptable. Once the numbers are known it is much clearer how hard your budget constraints are to meet and what measures are appropriate.

BTW: you can get down the controller chip to <30uA but getting a standard Arduino <30uA - no way. Either you modify it or you will not get even close.

Udo

  1. How much does your circuit consume currently under which exact conditions?

I haven’t tested it yet, because I’m missing some hardware parts. I can say that when it does nothing it needs <500 mA, when it update the display it needs 1500-2000 for a very short time.

2) How much capacity has the biggest acceptable battery?

I found an emmerich battery with 13000mAh, that would be ok.

3) How much capacity are you aiming at?
4) How much runtime are you aiming at.

Well, i’d like to run the circuit for at least a month without having to recharge it. I only have to power it up every 3 minutes or so, and even then it eventually doesn’t have to do anything.

So now we know that the average power consumption must not exceed 18mA.

You still did not tell how much current you will require and for how long. What are you actually doing? If you want help you have to provide more detailed information.

For example: why do you require a battery? And what are you actually trying to achieve? Why does your circuit draw up to 1.5A? Why does it have to be ethernet?

Udo

It’s a actually a doorsign, using a bistable lcd which displays status updates from twitter or any other internet-feed. It has to be ethernet because I can’t think of any other data-transfer solution which is that cheap and easy to use.
We thought about power-over-ethernet but that is not available in the target area.

What do you mean by how much current I will require? Isn’t mA current? The arduino+ethernet shield need about 350mA (from forums posts), but I will measure that, when I have time.

The power spike of 1.5A is the lcd when it updates, but that lasts only for 150ms or something (depends on the outside temperature).

Waht about Xbee? Xbee is designed for low power.

"mA" is a unit for current. But I was asking for how much current for how long. So now we know: 1.5A for 50ms for the LCD. Still we do not know for how long the ethernet has to run. Most probably much longer because it will need to connect.

I would go for xbee and get rid of the Arduino board. You can still use it for development but for the real application you should go for a less power consuming voltage regulator. A switching (buck) regulator would be a reasonable choice.

Udo

I could try Xbee yes, but I want to get most ouf of the hardware I already bought, and since it's "just" a bachelor project, i can't spend much more money on it.

The ethernet has to run for 1-5 minutes if there's an update (~5 times a day) and 30 seconds if there's no update.

Isn't it possible to build the circuit I initially suggested? I guess it would make a lot of people's life easier...

Ok, so basically you have no really tight power constraints. The only issue you should take care of is to limit the power consumption of you regulator.

Besides that you might want to follow this example: http://interface.khm.de/index.php/lab/experiments/sleep_watchdog_battery/

With regard to cutting the power of the ethernet shield: this can be achieved with a suitable transistor.

Of course you will need to tweak your hardware a little bit but this is the price for buying the hardware before researching the problem. It's considered part of the fun ;)

Udo

I finally built a working circuit which permits the arduino to cut it’s own power off and restart after some time. The thing in them iddle is a 555 timer.

EDIT: updated schematics, since i forgot a resistor
Please give me feedback: :wink: