[Microbit-Python] micro bit pin drive current

[Nigel Kendrick]

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_
> detailpage_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-
> bluetooth-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
>> >
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>
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