XO-1.75 microphone socket

[C. Scott Ananian]

On Tue, Nov 16, 2010 at 11:38 AM, Walter Bender <walter.bender at gmail.com> wrote:
> On Tue, Nov 16, 2010 at 11:19 AM, C. Scott Ananian <cscott at laptop.org> wrote:
>> On Mon, Nov 15, 2010 at 4:19 PM,  <forster at ozonline.com.au> wrote:
>>>> Just make sure you keep in mind the difference between the specification and what is likely to be acceptable.  One value is better suited to personal tinkering, the other to widespread propagation.
>>>
>>> Good point. As background to my questions Turtle Art 103 now supports sensor input.
>>> http://wiki.sugarlabs.org/go/Activities/TurtleArt/Using_Turtle_Art_Sensors
>>>
>>> As the specification stands, no teacher is going to conduct science experiments with external voltages. If the specification is changed to +-9v then they will have the confidence to conduct experiments with caution.
>>
>> Why not use 1.5V alkaline cells?  Or measure voltage from a lemon
>> battery?  I can think of any number of safe experiments.
>
> Why not indeed. See
> http://wiki.sugarlabs.org/go/Activities/TurtleArt/Using_Turtle_Art_Sensors#Lemon_battery

Right.  You can also do quite a lot of useful experiments using the
built-in 2V bias.   I'm not sure exactly what the problem is -- maybe
Tony can offer a more precise objection?  Perhaps he feels there needs
to be more guidance given on how teachers can construct "fool proof"
sensor experiments that are minimally dangerous to hardware, even if
the teacher isn't watching every kid every minute?
  --scott

ps. my rule of thumb would be "don't involve an external battery more
powerful than a lemon"  -- as I understand the protection circuits,
there's no way you can connect the internal bias voltage coming from
the microphone jack in a way that would damage the input.  You can
construct a lot of experiments (ie, most on the Turtle Art Sensors
page) which are thus "guaranteed safe, even if kids make mistakes" on
an XO-1.5/XO-1.75.  But the "measuring AC amps" example should be
moved to a separate "only with supervision and adequate care" page.
(Maybe also the "Generating electricity" example also, although it
would take a lot of turns of wire, a pretty strong magnet, and very
vigorous motion to exceed 9V.)  And the "Lemon battery" and
"generating electricity" examples should additionally be warned
against on the XO-1 --- maybe also the "burglar alarm", depending on
whether the XO-1 is always safe if its inputs are shorted.

-- 
                         ( http://cscott.net/ )