Short Battery Life

[jack0987]

I am using a ---
Arduino Pro Mini 328 - 3.3V/8MHz
https://www.sparkfun.com/products/11114
With a ---
SparkFun RFM69 Breakout (915MHz)
https://www.sparkfun.com/products/12775
I am powering it with 4 AA batteries connected to the RAW input.
Under normal operation it should only transmit or receive about six times a day.
My batteries seem to have gone dead in two weeks or less.
I had the system in an outdoor electrical box which got quite wet inside
and blew one of my Arduino minis which I replaced.
Might this be the cause?
What should I expect for battery life?
Is there a better way?

 

[Pommie]

Do you put the transmitter and Arduino in sleep mode between transmission?

Mike.

 

[Ian Rogers]

Also.. Both those devices run at 3.3v I'm sure they work down to 2.2v but alas the battery curve will be letting you down.

If you are using two by two 1.5 Alkaline / lithium to achieve 3v.. THEN!! A 1.5v battery is only1.5v for a short while... They spend most of their time at 1.1v so you will only have 2.2v to power your circuits...

If you are going to power these devices, make sure you A) Follow mike's advice and B) power from a 3.7v Lithium...

 

[Nigel Goodwin]

As already mentioned, you need to design for low consumption - both hardware and software. You also need to MEASURE what it is, under 100uA is generally low enough to make most products viable (and the sort of figure that's aimed at commercially).

Here's a short list of things you MUST do:

1) Switch the power to the RFM69 using a I/O pin, so you can switch power to it only when you need to.

2) Place the processor in sleep mode when not transmitting.

3) Use a low power 32KHz oscillator as the sleep clock, PIC's have this capability build in - presumably an AVR does as well? PIC's use TMR1 for sleep, and you normally set it to generate an interrupt every second, and use that to run an RTCC which also sets the trigger for the next transmission. There doesn't appear to be any such crystal on the Pro Mini, so you might need to choose something else?.

4) Make sure nothing is using power that doesn't need to - such as the LED on the Pro Mini - remove it.

5) There's a link on the Pro Mini board to bypass the regulator for low power applications, the datasheet of the existing regulator doesn't tell you how much it wastes - you might be better using an external regulator, and bypassing that one. The ones I'm using only use 16uA quiescent current.

If it's any help, I'm looking for 5+ years battery life, and probably transmitting once a day - using a PIC, with no special precautions (no sleep), and transmitting every 5 minutes (for crude battery life testing) I got over 5000 transmissions, and this is via a GPRS modem. As the PIC wasn't going to sleep, that wasted 6.5Ah battery life - more than your AA's could even provide.

So it's vitally important to use sleep, and you'll probably need to change your processor to something more sleep friendly?.

 

[jack0987]

So it's vitally important to use sleep, and you'll probably need to change your processor to something more sleep friendly?.

Have you looked at this equipment?
It appears they have low stock. Are they going out of business?
https://lowpowerlab.com/shop/

 

[jack0987]

Do you put the transmitter and Arduino in sleep mode between transmission?

Mike.

Hi Mike.

The serial stuff is still in my code.
If I remove it, will there be a power savings?

 

[Pommie]

Between transmissions you tell the transmitter to go into sleep mode - see datasheet. Plus you put the Arduino into sleep mode. You should end up using less than 0.5mA and hopefully much less(20uA). You will have to unsolder the power LED.

 

[Nigel Goodwin]

Have you looked at this equipment?
It appears they have low stock. Are they going out of business?
https://lowpowerlab.com/shop/

No idea, but I don't see the connection between 'low stock' and 'going out of business'?.

I've not looked at them, as I'm not interested in using a module, just a bare IC - and preferably a PIC

But as we've all told you, and as that website says, you MUST put the processor in sleep (and obviously must have some method of waking it up again when needed) - and as I also said, remove power to the transmitter as well.

 

[jack0987]

Between transmissions you tell the transmitter to go into sleep mode - see datasheet. Plus you put the Arduino into sleep mode. You should end up using less than 0.5mA and hopefully much less(20uA). You will have to unsolder the power LED.

The way it is right now is that it waits for a magnetic switch to open or close and then it sends a transmission indicating the state of the switch each time it changes.

The only thing I can think of is that I will have to have it sleeping and wake it on any change of switch state.
I have been looking on google to learn about this.

Please advise.

 

[Pommie]

Have a read of https://learn.sparkfun.com/tutorials/reducing-arduino-power-consumption

And the transmitter datasheet has details of putting that to sleep as well.

Mike.

 

[Nigel Goodwin]

The way it is right now is that it waits for a magnetic switch to open or close and then it sends a transmission indicating the state of the switch each time it changes.

The only thing I can think of is that I will have to have it sleeping and wake it on any change of switch state.
I have been looking on google to learn about this.

I can't comment on Arduino, but on a PIC I use TMR1 to wake up every second to run the RTCC, and 'interrupt on change' to wake up from a switch change, and process the action. I know the Arduino has some interrupt input pins, and I presume they can be used to wake up from sleep?.

 

[Pommie]

I read an article a couple of days ago about putting Arduinos to sleep and only waking on key change interrupt. With the power LED disconnected they were using just a few micro Amps. Alas, can't find the article now but it can be done.

Mike.

 

[Nigel Goodwin]

I read an article a couple of days ago about putting Arduinos to sleep and only waking on key change interrupt. With the power LED disconnected they were using just a few micro Amps. Alas, can't find the article now but it can be done.

Mike.

I presumed it could, as it's an obvious requirement for a micro-controller.

 

[jack0987]

Have a read of https://learn.sparkfun.com/tutorials/reducing-arduino-power-consumption

And the transmitter datasheet has details of putting that to sleep as well.

Mike.

As a first step, I followed the tutorial you mentioned above and the power usage dropped from 20.4ma to 16.5ma.

For the second step, I disconnected one end of the onboard power LED.
The board will no longer accept an upload.

 

[Pommie]

Disconnecting the power LED cannot cause the board not to accept uploads. You must have done something else. Double check what you did.

Mike.

 

[jack0987]

Disconnecting the power LED cannot cause the bourd not to accept uploads. You must have done something else. Double check what you did.

Mike.

Not sure yet.

I reconnected the power red LED since I only lifted one end of it and it is back to accepting uploads.
There is a green LED near pin 10 that is staying lit and sometimes it goes out. I do not think it should be doing that.

 

[Pommie]

If you look at the schematic the LED is next to an isolation pad. Could you have unsoldered that?

Mike.

 

[jack0987]

If you look at the schematic the LED is next to an isolation pad. Could you have unsoldered that?

Mike.

I looked at it under my 4x magnifier and everything looks good.
No solder bridges, nada.
when I run my finger along the pins near pin 10 the green LED there goes out
and sometimes it goes out on its own.

Well, guess I'll have to order up another pro mini so it will be a while before I am back online.
Shucks. Just as I was having fun.

 

[Pommie]

Why can't you reconnect the LED to try and work out what went wrong?

Mike.
Edit, the solder pad should be bridged to power the board.

 

[Pommie]

Found the article. **broken link removed**

Mike.