Author Topic: Running Moteino from 2 x AAA cells  (Read 10930 times)

TomWS

  • Hero Member
  • *****
  • Posts: 1929
Running Moteino from 2 x AAA cells
« on: October 25, 2014, 09:37:35 AM »
I'd like to run Moteino from 2 Lithium AAA cells because these have plenty of power and fit nicely inside a 1" PVC tube.  However, with the MCP1703 LDO, there is more voltage drop than I'd like.  Looking at the high level circuit of the MCP1703 (and its low quiescent current), it seems to me that connecting the battery supply to both the PWR and the 3.3V pins shouldn't cause any problem with the 1703 and eliminates the dropout voltage.

Does any one have any experience with running Moteino from two AAA (or AA) cells?  And how have you hooked them up?

Tom
PS: I'd rather not unsolder the MCP1703...

Felix

  • Administrator
  • Hero Member
  • *****
  • Posts: 6522
  • Country: us
    • LowPowerLab
Re: Running Moteino from 2 x AAA cells
« Reply #1 on: October 25, 2014, 10:33:17 AM »
You could use a small LiPoly instead which gives you plenty of head room.
Also at 3v you are grossly overclocking the 16mhz Moteino. You could change the fuse to run on the internal 8mhz oscillator instead but you should also desolder the regulator.

Spexx

  • NewMember
  • *
  • Posts: 30
  • Country: de
Re: Running Moteino from 2 x AAA cells
« Reply #2 on: October 25, 2014, 03:25:46 PM »
As already mentioned from Felix, I think the best way would be if you remove the regulator and change the frequency to 8MHz. I have running some Moteinos in this configuration with 2xAA batteries since several months without problems.

ColinR

  • Full Member
  • ***
  • Posts: 176
Re: Running Moteino from 2 x AAA cells
« Reply #3 on: October 25, 2014, 04:10:53 PM »
Go LiPo!
CuPID Controls :: Open Source browser-based sensor and device control
Interfaceinnovations.org/cupidcontrols.html
cupidcontrols.com

TomWS

  • Hero Member
  • *****
  • Posts: 1929
Re: Running Moteino from 2 x AAA cells
« Reply #4 on: October 26, 2014, 09:30:20 AM »
You could use a small LiPoly instead which gives you plenty of head room.
Also at 3v you are grossly overclocking the 16mhz Moteino. You could change the fuse to run on the internal 8mhz oscillator instead but you should also desolder the regulator.
The last thing I want is a rechargeable battery.  I want to deploy these units in the field (quite literally) and forget about them for 2-4 years.  I also want them to stand up to harsh weather conditions, although not as severe as Michigan  ;) hence the choice of Li FeS2.  A couple of AAA batteries will give me 1250mAh capacity, operate as low as -40C, have LONG shelf life, and, as I said, will easily fit in a PVC/Copper tube with a Moteino on one end and my sensors on the other.  Also, a couple of fresh batteries will have an open circuit voltage of ~3.6V and, while operating an active Moteino, drops down to about 3.2V nominal. 

I do like your suggestion about dropping to 8Mhz as this should be plenty of performance for these applications although 3.2V at the processor would be better than running at 3.7V at the PWR pin with 0.63V dropout at the regulator.

Also, I agree about pulling the regulator from the board.  I had overlooked the fact that it is going to try to drive the output to 3.3V and can't so the current draw will be higher than quiescent due to this (as shown in the Ground Current curve, figure 2-4, in the MCP1703 spec).

Regarding changing the frequency to 8MHz, you say I could "change the fuse".  This sounds pretty drastic and permanent.  Is it?  And, if the base frequency is changed, do the standard delay(), millis(), etc still work properly or do these need to be scaled???

Thanks for the suggestions,
Tom

TomWS

  • Hero Member
  • *****
  • Posts: 1929
Re: Running Moteino from 2 x AAA cells
« Reply #5 on: October 26, 2014, 06:34:37 PM »
As already mentioned from Felix, I think the best way would be if you remove the regulator and change the frequency to 8MHz. I have running some Moteinos in this configuration with 2xAA batteries since several months without problems.
Two questions:
1. Do you use wireless programming to update your code?  If so, did you need to make changes to the bootloader?
2. How did you change to 8MHz?  (new resonator, change to prescaler, or fuse change to set clock to internal 8MHz RC clock)

Tom

Spexx

  • NewMember
  • *
  • Posts: 30
  • Country: de
Re: Running Moteino from 2 x AAA cells
« Reply #6 on: October 27, 2014, 09:41:03 AM »
To your questions:
1. I don't have tested the wireless programming with the 8MHz clock, but I think there shouldn't be any differences because there are no changes to the bootloader needed.

2. I have only changed the fuses (low:0xE2, high:0xDA, ext:0x07) to set the clock to internal 8MHz and I have also disabled the BOD (if I remember me correct, the RFM-module will work down to approx. 2.4V).

I have running a Moteino with 8MHz and with a humidity/temperatur sensor (SHT15) since May '14 with 2xAA batteries. At the beginning the voltage was at 3.31V, and now 5 months later the voltage is at 3.17V. The Moteino is sleeping all the time and will be only waked up every 40 seconds to send the humidity/temperature to the base station. I think it should work furthermore for several months :)

Regards,
Christian

TomWS

  • Hero Member
  • *****
  • Posts: 1929
Re: Running Moteino from 2 x AAA cells
« Reply #7 on: October 28, 2014, 07:35:19 PM »
Christian,
thank you for the feedback.  I appreciate it.  To clarify, with the changes you made, do delay() and millis() still work properly without any code changes?  Maybe with reduced accuracy, but that's ok for me.

I've used other wireless monitors with Lithium AA batteries, with updates every ten minutes (our weather doesn't change THAT rapidly  :)
and had batteries last for over 4 years in relatively severe conditions (+118 degrees F).  Ironically, solder joints fail before the batteries do!

I may just put a voltage boost circuit in so that I can run at full 3.3V at the processor and not worry about any code changes or compatibility issues, but I do thank you for the fuse settings to enable 8MHz.  This will help me and others, I'm sure.

Tom


Spexx

  • NewMember
  • *
  • Posts: 30
  • Country: de
Re: Running Moteino from 2 x AAA cells
« Reply #8 on: October 29, 2014, 09:16:10 AM »
Hi Tom,

yes sure, delay() and millis() will work properly without changing the code. The only thing you have to do is to change the f_cpu setting. In case of using the Arduino IDE, you will find in the program directory under \hardware\arduino a file named "boards.txt". You can add another board for the Moteino, where you can set the clock speed to 8MHz.

For example, I have added following lines:
Code: [Select]
Moteino8.name=Moteino@8MHz (D9-LED, BOD disabled)
Moteino8.upload.protocol=arduino
Moteino8.upload.maximum_size=32256
Moteino8.upload.speed=57600
Moteino8.bootloader.low_fuses=0xE2
Moteino8.bootloader.high_fuses=0xDA
Moteino8.bootloader.extended_fuses=0x07
Moteino8.bootloader.path=optiboot
Moteino8.bootloader.file=DualOtiboot_atmega328_1k_d9LED_debugOFF.hex
Moteino8.bootloader.unlock_bits=0x3F
Moteino8.bootloader.lock_bits=0x0F
Moteino8.build.mcu=atmega328p
Moteino8.build.f_cpu=8000000L
Moteino8.build.core=arduino
Moteino8.build.variant=standard

If you start the Arduino IDE, you will find this new board. So you only have to choose the correct board before uploading a new sketch and delay() and millis() will work as before. :)
But as already mentioned in this thread, first of all you have to change the fuses.

Hope this will help you.
Christian

TomWS

  • Hero Member
  • *****
  • Posts: 1929
Re: Running Moteino from 2 x AAA cells
« Reply #9 on: October 29, 2014, 06:01:36 PM »
Cool!  Thanks!  I'll try it out, maybe by this weekend, but, because of all the new ideas I have with Moteino, my project list is pretty huge!

Thank you for taking the time to answer.

Tom

TacticalSnack

  • NewMember
  • *
  • Posts: 6
    • TacticalSnack Blog
Re: Running Moteino from 2 x AAA cells
« Reply #10 on: November 15, 2014, 08:12:57 PM »
I too have been interested in running off 1 or 2 AA/AAA cells. I ran across the LTC3525 on JeeLab's http://jeelabs.org/2010/09/06/running-off-a-single-aa-battery/

TomWS

  • Hero Member
  • *****
  • Posts: 1929
Re: Running Moteino from 2 x AAA cells
« Reply #11 on: November 16, 2014, 08:07:04 AM »
I too have been interested in running off 1 or 2 AA/AAA cells. I ran across the LTC3525 on JeeLab's http://jeelabs.org/2010/09/06/running-off-a-single-aa-battery/
I agree a booster is necessary if you're trying to work with a single 1.5V battery.  If I can fit a 3V source, however, then dropping back to 8Mhz works for me and is a much lower cost and more efficient solution.  If you need a booster, however, the LTC3525 seems VERY expensive to me.  My quick glance at Digikey prices this higher than the AtMega328P!   Alternatives I've looked at are: NCP1402 and MCP1640.

Tom

Saxx

  • NewMember
  • *
  • Posts: 10

Felix

  • Administrator
  • Hero Member
  • *****
  • Posts: 6522
  • Country: us
    • LowPowerLab
Re: Running Moteino from 2 x AAA cells
« Reply #13 on: November 16, 2014, 06:02:47 PM »
I've had very bad luck with such ebay no name boosters. They just don't work or behave very erratically.
I see the one you shared has a LED onboard?!

TomWS

  • Hero Member
  • *****
  • Posts: 1929
Re: Running Moteino from 2 x AAA cells
« Reply #14 on: November 16, 2014, 06:44:17 PM »
Maybe this could be of interest? I just ordered 2.

http://www.ebay.com/itm/DC-DC-Input-0-8-3V-Output-3-3V-Step-UP-Power-Converter-Voltage-Module-RF-/231083181020?pt=LH_DefaultDomain_0&hash=item35cda183dc
Well, that is a choice.  I was specifically referring to the booster ICs themselves and making my own, when the need arises.  As Felix points out, some of the no-name modules are poor quality. 

The chips are SOT packages which are fairly easy to hand solder (for those of us who aren't in mass-production like Felix) and the rest of the parts are low cost and readily available.