Data Logger Shield current consumption results

[Lapatate]

I've made some mesurments on the power consumption of the Data Logger Shield together with a Atmega328. This was relevant for a a long time logging project. The values are to be associated with the following set-up:

Basically the data logging shiel from Adafruit is directly controlled through the Atmega328 on a breadboard with an external oscillator 16Mhz.

Current when iddle: 26.4 mA

Current in Power Down mode with Watchdog Timer: 0.45 mA

I needed to reduce the power consumption as far as possible, that's why the Atmega is on a breadboard without the arduino periferals that all consume a little current even when the controller is in sleep mode. The watchdog timer is used to wake from sleep once every 59.5 seconds (looping 115 times for 0.5 sec) and the measurents are taken and written to the SD card, the RTC of the Logger shield triggers the controller back to sleep every full minute. The result is approx. 0,5 sec of processing and 59,5 sec of power down mode.

With a Lipo battery of 1730 mAh this allows for app. 90 days operation with a 1 measure every minute.

Gives lot of reasons to be zen...

[adafruit_support_bill]

Nice work! A lot of people ask about low-power operation and will be interested in your results.

[Lapatate]

The previous values where approximativ as the current measured over a 0,5sec interval for logging, so repeating the measurements with more time for the "wake" mode and for every component seperately to see what is consuming how much.

In the earlier described configuration

During Processing, Read-out and Logging:

Data Logger Shield: app. 14.6mA
Atmega328-PU at 16Mhz with external oscillator: 12,9mA
The DHT22 Temperature and Humidity sensor: 1,5mA

Total app.: 29mA

During sleep(Power Down with WDT), no sensor read-out:

Data Logger Shield: 0,160mA
Atmega power down with WDT enabled: 0,28mA
The DHT22 Temperature and Humidity sensor (no readout): 0,012mA

Total app.: 0,45mA

All elements in the circuit are powered at 4,9V through a lipo Rider.

Enjoy your week-end!

[Lapatate]

After further looking into the power saving method it seems the Watch dog timer can be quite usefull when you need the AVR to sleep for longer periods and then to wake up on the choosen interval . To precisely use timing and WDT Prescaler better accuracy can be obtained considering the WDT frequency from graph 29-35 of p345 from the ATmega documentation than the frequency metionned in WDT description on page 54.

The WDT clock is really near 112.5Khz at room temperature and 5V rather than 128Khz which can make difference of a couple of ms for the typical timeouts.

If your WDT is not doing what you want this might the glitch.

[Cra451]

Do you have any docs/links on how the watchdog timer works?

[Cra451]

I found a couple of links on watch dog timers. For my data logger some of the sensors are slow so the 8 second setting worked for me.

http://tushev.org/articles/electronics/ ... hdog-timer

http://www.nongnu.org/avr-libc/user-man ... chdog.html

[Lapatate]

Hello,
A very simple and examplary application using WDT and SLEEP is probably this one:

http://interface.khm.de/index.php/lab/e ... g_battery/

It'll probably turn up in various threads about this topic. For the rest I used the ATmega documentation for more in deept timing settings and sleep modes.

Regards,
Lapatate

[bethesdakid]

Thanks, this is an extremely significant advancement.
My system cant be accessed to change the 4 rechargeable AA batteries or remove the SD for at least 4-5 months.

Data is to be acquired 7 times a day.
Environment is fairly stable at around 55 to 85 F.
4 rechargeable AA batteries can fit in the space or one 9v.
Batteries changed only 4-5 months.

Your program will extend battery life. however, several issues...
A. dont know how to connect the SD to the MAC. Do I need to make a cable w/SD female and USB male?

B. Instead of SD, can the Arduino and RTC write to an USB flash drive? then just plug int MAC
You have ideas on doing this configuration? Can the standard cable to upload programs to the Arduino be revised to have the male USB at the MAC replaced with a female USB and then upload to the Arduino FROM the USB flash and then ECHO TO SERIAL TO the USB flash?

Whatcha think???

[adafruit_support_bill]

Writing to a USB flash drive from the Arduino is not possible (at least not without getting pretty deep into USB protocols).

But most computers these days have SD card slots because that is a common format for digital cameras. Check the specs for your Mac, if it is of recent vintage it likely has one.