Let's Make Robots!

So, this weather hmm?

Ok, this blog is meant to post content related to the progress of my little garden monitor.

Objectives:

- Low power node (using an atmega chip)

- Measures: temperature, humidity, luminosity, soil moisture

- Reports it back to a central node (via nRF24L01+ modules) at specified time intervals

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October, 25th 2013

And here is yet another iteration, this time it was validated through Seeedstudio DRC's rules (I'll probably have them made there if the breadboarding passes the tests) and also had the input/tweaks of Great Eagle Master Bajdi!

(click to enlarge)

I had to "ugly up" the schematics part... because I was having an error I couldn't make go away, and well since the layout is more important in the actual board I didn't cared much.

(click to enlarge)

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October, 22th 2013

Ok, I finally "finished" the circuit (for examining & testing) and took a stab at a complete board routing.

 

(click to enlarge)

 

(click to enlarge)

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October, 17th 2013

After, some slow iterations over the last few days I further modified my initial (and incomplete) schematics draft into a Rev. 2 where I hope I've included everyting I want/need on this board. I may cut stuff out if I find I can't route everything into a desirable footprint.

(click to enlarge)

 

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October, 12th 2013

Currently I'm at the stage of circuit design/breadboarding tests. Also I already have code to take all measurements, now I just need to mesh it with RF24 code and try to make it as small as possible so it fits an atmega8 (preferably).

This was my first tentative circuit (rev1):

 

 

 

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October, 12th 20113 and

October, 17th 2103 ?

 

Me thinks Kariloy has been time traveling...

 

Perhaps, but this would be like robbing the bank and getting caught because of a parking ticket! :P

And posting stuff at 2 A.M. is not always the best idea... ;_;

 

Also, if you're in the mood to catch "time travellers" I invite you to go through Hoff's photo collection :P

I don't know if you've seen SparkFun Nordic fob or not, but it may give you some ideas on using the nRF24L01+ in low power mode.

I'm not sure if it would be practical or not but it may be possible to power some low current sensors from an I/O pin. I've had mixed results powering a nRF24L01+ module from a Propeller I/O pin. A couple of modules worked on I/O power but most of the ones I tried didn't work correctly when powered from an I/O pin.

Well I do what that part covered (in theory). I've been using the nRF24l01+ on some of my applications with the RF24 library, so I'be been having this under my eye.

So the plan yeah, is to make the radio and whatever I can make sleep for X amount of time, wake-up, take reading and send them, then back to sleep. So that coupled with the solar cell should (hopefully) get me a long run time. Well at least sometime goes wrong due to bad design :P

 

Don't forget to put some caps at the input/output of the voltage regulator and near the VCC pins of the ATmega. Don't have to be big caps. I would also replace the BAT42 (that's a signal schottky diode) with another schottky diode with a lower forward voltage. BAT42 has a forward voltage of 400mV at 10mA current and 1V @ 200mA. You should be able to find schottkys with a lower forward voltage.

How will you switch between battery power and the solar panel? Now the VCC of battery and solar panel are tied together?

I think I got the BAT42 suggested off somewhere for a similar application, I mean I didn't have them arrived. Anyhow, I don't expect to draw more than 10mA out of the solar panel. Plus I'm not too good at finding components with specific requirements, the BAT42 was my finding after searching for quite a while :P

well, they are parallel to each other (batt and solar panel), so it shouldn't be a problem? I may have mis-drawn it, because I've used a couple of individual pads to represent the battery, since I don't have a specific part for it in Eagle, nor I was eager to make one/look for one! But yeah, regardless I'm feeling a bit dumb/unsure about that myself. :s

 

For low power operation there are lots of tricks you can play.  The atmega8 datasheet http://www.atmel.com/Images/Atmel-2486-8-bit-AVR-microcontroller-ATmega8_L_datasheet.pdf has lots of good info.  Start on pg 35.  A few notes:

1.  Turn off peripherals you aren't using or ones you are using when not being used.  There are registers to turn off most peripherals.

2.  Use sleep modes when not doing anything.  Use a timer to wake up ever so often.

3.  Use slow clocks.  Instead of running at 8 MHz, use the clock divider or a different clock (watchdog).  Slower clock means less power.  You can switch back to full speed when needed.

1 . black magic... must look into it

2. that is the plan :)

3. I was thinking 8MHz because it was easier to mooch part of the work of someone who already done something like running @ 8MHz

Regardless, I think I may still be stumbling/tripping over simple stuff in the circuit design :s

 

I'm liking this idea Mr. Clementime. Not sure if Processing is your cup of tea but having a centrelized computer graphic display of all readings would be farily nifty. Bet you could probably use something else, just Processing for me is what comes to mind.

Well, I have some other plans that do not include Processing and yet include visualization :P