Author Topic: Beginner Here - Going Low Power  (Read 1248 times)

tonto

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Beginner Here - Going Low Power
« on: August 23, 2014, 07:38:48 AM »
Firstly a huge thank you to Felix for the awesome Motenio units.  Had spent hours researching arduino, radio and sensors.  Found loads of stuff and still have sitting in the kit back some Zigbee units and Ciesco units and then I found Motenio and haven't really found time to play with them yet (hopefully I will).

I am very much a re-beginner to electronics and refound it after falling in love with the Raspberry Pi (what an awesome set of kit to learn linux with) and then looking at how the Pi can extend out into the real world.

My project:
Multi faceted as I want home automation.  Turn on few lights and green house heater etc , then also water my plants and have them run of the Raspberry Pi.  It is low power and flexible.  Sub context has also been to reduce my energy costs.  Big shout out to http://www.desert-home.com/.  So much cool information there and I have the same issue living in Australia, our energy costs are horrific. 

Tools in the Kit so Far.
WEMO - Took me a long time to settle on the WEMO (and there is alot of negative stuff about them).  Key reason I went with Wemo to control my main power stuff is that they are relatively low cost (AUD $56 ish) for the switch, with WIFI.  A WIFI chip here will cost me about $35 AUD alone.  They are fully AUD regulation certified, and big factor is that there are now some really good Python Libraries available to control them.  I've currently played with the libraries (they do work) however at this stage still using the WEMO control software, with very good results. 

RASPBERRY PI
I just love these units.  They are very low cost and yet so powerful (manage your expectations here on the processing power).  Another big shout out to Raspberry XBMC, is amazing and I use it everyday (my apple TV is getting dust).

MOTENIO
Wow, these units are just so cool, builds all the remote stuff into one small very affordable unit and the library from Felix works brilliantly.  Played around learning it as my learning curve and settled on using the Strut example as way to go for remote sensors (saves heaps of issues with converting floasts etc).  So far I've just been able to wack it into a Strut and the gateway gets it

MAIN QUESTION
Okay, sorry for the preamble, just wanted to provide some content here.  Been reading helibot43 and learning heaps from his work.  I ran into a similar problem with my first remote sensor project.  A basic DHT22 on a motenio with 9 volt battery sending every minute with the lowpower sleep library utilised. 

Worked well for a month, but then it died, might have been that the greenhouse went upto 50degrees C which I am sure will kill any battery, but didn't seem right.  So I went off and had a think about the circuit (which in further investigation I got wrong as well), damn old eyesight.  However the thought was still valid.

So question.  When the motenio goes to sleep does the DHT22 still receive some power?  I could spend time working this out, but thinking why not check if someone has done this before.

Then, building on this.  I want to have more sensors attached to my greenhouse sensor.  (A dallas prob for soil temp and soil moisture sensor - ex ebay - gonna bite me there).

Now the big question.  What if I attached all these sensors to a power bar that is control by a transistor circuit and the base is controlled by Motenio?  Say Pin 5.  During sleep mode we power down Pin 5 (so all sensors are off) then when we want a reading 5 mins later (using an appropriate lib) when we power up with take Pin 5 high, wait 1sec so they can do their stuff, take the readings, then power down again?

Have I missed something here, the just having a normal powerdown of the motineo cuts the power to the sensors or are they still drawing some power?

Please go easy on me here.  I'm learning!  thanks

David



Felix

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Re: Beginner Here - Going Low Power
« Reply #1 on: August 25, 2014, 08:31:24 AM »
Hi David, welcome to the forum and thanks for your kind words.
To save power you will need to make sure none of the sensors draw power continuously, in addition to putting the Moteino and the radio (and FLASH if any) to sleep. Actually the FLASH is already in micro amps when not used but could be futher put to deep sleep for sub micro amp power.
Any sensors that are powered directly from your battery or the 3.3V Moteino output will eat your battery.
The transistor approach works fine, I started with that back when I created my first mailbox notifier (http://lowpowerlab.com/blog/2013/03/01/mailboxnotifier-moteino-based-mail-event-notifier/)
Then I realized such a small sensor could just be powered directly from a Moteino digital pin so I ditched the transistor and I only power the sensor during wakup, take the reading, then power down everything again for a few 8sec cycles.
There are many ways you can cut power to your sensors. The transistor/mosfet approaches just work if done correctly. Many google resources there.
Hope this helps.
-Felix