some first impressions

Arjun Sarwal arjun at
Wed Aug 15 06:57:35 EDT 2007

Hello all,

Thank you for your emails.

1) eToys:
It would be very nice to have support for Analog Input in eToys.

You could use my code -

(getting samples)

(toggling between AC/DC modes and controlling bias voltage etc.)

Or I could easily provide you with a class that you could use. I could make
functions in that class that could simply return to you the required values.
For example there could be a function that you could call to return avg
voltage or rms voltage, select between ac/dc modes, set bias_on, set

Let me know if I can help in any way.

I have opened the following ticket . See here -
I have not assigned the ticket to any one nor set a time line for it as of
now. Please feel free to set those.

2) Output Analog/Digital:
The USB is an interesting idea as I had discussed with Mitch. I could simply
make a board using a USB to parallel kind of a chip. I will be getting down
to doing something similar shortly.
Anybody would suggest to explore audio out for a similar purpose ?

3) Other ideas for sensor input :
Mitch and Wad had suggested regarding exploring some basic medical
applications using the Analog Input port. For example maybe be able to
measure pulse rate ...
I am quite excited about these ideas and plan to think about things to do on
these lines too. Any initial suggestions ?


On 8/11/07, Mitch Bradley <wmb at> wrote:
> Hal Murray wrote:
> >>  - some parallel port (or similar) should be made available, for
> >> children to play with in physics. I remember playing with a PC
> >> parallel port with some simple software to turn leds on and off. When
> >> you are a kid, being able to send commands to projects you create is
> >> great (think about modern legos, but using simpler stuff like leds,
> >> motors, etc) : it translate the "virtual part" ie the software you
> >> create on the computer to the "real world" where you make leds blinks
> >> in sequence, or a motor move.
> >>
> > ...
> > There are USB connectors.
> >
> > ...
> > USB to printer port adapters are also available.  I've never played with
> one.
> >  Prices are under $40.
> >
> >
> > There are also things like this with 24 GPIO lines.
> >   USBIO24R
> >
> >   US distributor:  $75
> > ...
> >
> > There is also the microphone input and audio output for A/D and D/A.  I
> think
> > the XO hardware supports a DC coupled mode.
> >
> > We should work on a collection of hacks to demonstrate how they work and
> a
> > list of which ones are known to work.
> >
> OLCP just had a summer intern, Arjun Sarwal, who developed some low-cost
> gadgets to plug into the mic port - temperature sensor, intrusion
> detector, etc.  He plans to document them and set up a framework for
> documenting other similar hacks.
> We also talked about an OLPC digital gadget prototyping dongle with a
> USB-equipped microcontroller like those available from, for example,
> Atmel.  Those chips cost a dollar or two and Arjun can get all the other
> parts really inexpensively in India where he lives.

Arjun Sarwal
One Laptop Per Child
arjun at
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