[Testing] [OLPC New Zealand] New prototype XO-1.75s in Auckland, New Zealand

[Walter Bender]

On Wed, Aug 24, 2011 at 6:48 AM, Tom Parker <tom at carrott.org> wrote:

> On Wed, 2011-08-24 at 07:38 +1000, James Cameron wrote:
> > On Tue, Aug 23, 2011 at 10:39:38PM +1200, Tom Parker wrote:
> > > Nice! I made a simple "position the turtle based on accelerometer x and
> > > y" and found the sensor to be quite noisy.
> >
> > Could you quantify that please?
> >
> > Normal shaking of hand, or the earth under you in your case, or nearby
> > sound, may generate what appears to be noise.
>
> I must say I hadn't thought about where the noise might be coming from,
> I merely wanted to process it out. Is it really sensitive enough to pick
> up normal sound (not just boom sounds!)?
>
> Going back to what I was trying to do, I was trying to make a spirit
> level, so I'm not interested in vibration. I'm interested in enough
> averaging to smooth out the noise (whatever the source) while retaining
> enough speed to such that the turtle moves smoothly.
>
> I'm not really familiar enough with Turtle Blocks to know if the
> performance I am seeing is because reading the sensor is slow or because
> computing the average is. I had the blocks turned off because my program
> was in the way of seeing what was happening and I did discover this
> greatly speeds things up, but updates were still slow enough to make
> finding the zero point difficult.
>
> I suppose exposing the raw data is good for teaching about the
> properties of the sensor and the real world (if it is indeed picking up
> small vibrations). However I suspect many applications would like some
> signal processing and a lot of those would like fast signal processing.
> If the sensor is up to it but turtle blocks itself isn't, perhaps some
> signal processing could be built in. Either as a separate "average n
> values" block, or a property of the accelerometer block?
>

You could create such a block in Python and import it into your Turtle Art
project. See
http://wiki.sugarlabs.org/go/Activities/TurtleArt#Programmable_Brick

You can also do in-line math using the 'Python' block, as per Tony's example
or: http://wiki.sugarlabs.org/go/File:Sine.png


>
> Then you can have a conversation about the sensor and signal processing
> without having to introduce loops and boxes?
>
> There might also be a use case for a "zero" transformation where you
> declare the current orientation as zero and thereafter return the offset
> from that. My vector math isn't quite good enough to work out how to do
> that, never mind express it in Turtle Blocks. I say this because the
> first thing I did was wonder why only one axis was near zero with the
> laptop sitting "flat". I quickly realized the sensor is in the screen
> and the screen was tilted backwards!
>
> Can you make subroutines in turtle blocks? My program was a bit unwieldy
> with just two loops in it. I guess I should look at the examples.
>

Yes. See the blocks palette:
http://wiki.sugarlabs.org/go/Activities/TurtleArt#Blocks_Palette

>
> Also, we're more than 750km from Christchurch, I didn't feel any of the
> big earthquakes, never mind the (still numerous) aftershocks.
>
>
good luck.

-walter


-- 
Walter Bender
Sugar Labs
http://www.sugarlabs.org
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