[Microbit-Python] micro bit pin drive current

[Nigel Kendrick]

Minor correction - the NJM2113D is a class AB chip. I was also playing
around with a class D chip from Texas Instruments, but used the JRC part in
the end.

-- Nigel

On 1 Sep 2016 12:36, "Nigel Kendrick" <nigel.kendrick at gmail.com> wrote:

> I use a 3v class D bridge amp chip from JRC (NJM2113D - RS Components sell
> them) that works well with the micro:bit.
>
>   -- Nigel
>
> On 1 Sep 2016 11:26, "David Whale" <david at thinkingbinaries.com> wrote:
>
>> That is true, but unfortunately it is only part of the story.
>>
>> It's not the pin drive current that could be the problem, it's the
>> opportunity for an inductive load (a speaker) to cause back-emf that is
>> above the specified pin voltage of the GPIO pins. Although I haven't done
>> the maths or looked at a scope trace to see how high in voltage the
>> back-emf peaks are at given frequencies, it might still be ok in practice
>> without any coupling or protection given the range of frequencies in use..
>>
>> However, I spoke to Nicholas Tolervy about this resource, and he uses a
>> powered speaker such as this:
>>
>> https://www.amazon.co.uk/gp/product/B0039YP37E/ref=oh_aui_de
>> tailpage_o09_s00?ie=UTF8&psc=1
>>
>> connected with one of these:
>>
>> https://sciencescope.uk/product/bbc-microbit-sound-cable-2/
>>
>>
>> I also use one of these...
>>
>> http://www.maplin.co.uk/p/kitsound-pocketboom-portable-bluet
>> ooth-speaker-green-n54dc
>>
>> Which, incidently, has a nice bass response that works really well with
>> this fab Python resource!!
>>
>> https://www.microbit.co.uk/musicfest/that-bass
>>
>> It's very loud with some powered speakers, in my experience, so in some
>> environments you should consider a volume control of some sort!
>>
>> Hope this helps.
>>
>> David.
>>
>>
>>
>>
>> ___________________________________________________________
>> David Whale, B.Sc (Hons), MIET
>> *Software Engineer and IET Schools Liaison Officer, Essex*
>>
>>
>> On 31 August 2016 at 07:23, Damien George <damien.p.george at gmail.com>
>> wrote:
>>
>>> There are no additional buffers on the pins.  The microcontroller will
>>> source/sink its maximum current and then the output voltage will begin
>>> to drop to keep the current at that maximum (and so act like a current
>>> regulator/limiter).
>>>
>>> On 31 August 2016 at 15:48, fresh.bread via Microbit
>>> <microbit at python.org> wrote:
>>> > I'm a bit worried by the diagram on the documentation for the
>>> micropython
>>> > speech module showing a loudspeaker connected directly to pins 0 and 1
>>> (see
>>> > http://microbit-micropython.readthedocs.io/en/latest/tutoria
>>> ls/speech.html)
>>> >
>>> > What is the maximum drive current for the pins. The processor chip only
>>> > seems to be able to sink/source 0.5ma (or 5ma in high current drive
>>> mode)
>>> > .Are there additional buffers connected to pins 0,1,2 that allow a
>>> higher
>>> > current?
>>> >
>>> > Jim
>>> >
>>> > _______________________________________________
>>> > Microbit mailing list
>>> > Microbit at python.org
>>> > https://mail.python.org/mailman/listinfo/microbit
>>> _______________________________________________
>>> Microbit mailing list
>>> Microbit at python.org
>>> https://mail.python.org/mailman/listinfo/microbit
>>>
>>
>>
>> _______________________________________________
>> Microbit mailing list
>> Microbit at python.org
>> https://mail.python.org/mailman/listinfo/microbit
>>
>>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/microbit/attachments/20160901/40089c54/attachment.html>