[Microbit-Python] More musical silliness

Fri Oct 16 01:27:26 CEST 2015

Given more time, it would be possible to double the loudness of the
current music output.  It can be done by connecting the speaker to
pin0 and pin1 (instead of pin0 and gnd) and driving pin1 opposite to
pin0 (so pin0 high would have pin1 low, and vice versa).  This gives
double the voltage swing on the speaker.

The nRF chip is capable of doing this.  It just requires some coding.

On Thu, Oct 15, 2015 at 11:59 PM, Michael <sparks.m at gmail.com> wrote:
> Yep, the catastrophone (and sorting hat) required a basic low pass filter
> and single transistor amplifier circuit - which is a bit of a barrier.
> Leaving the door open though is good.
>
> (The cat piano/catastrophene came out of my daughter seeing this  Jools
> Holland's Hootenanny : https://www.youtube.com/watch?v=fkZp_uTbIKk abd
> asking me if I could make her one...)
>
> Getting it loud enough for a public performance is harder than you might
> expect, so the approach taken at present is really cool.
>
>
> Michael.
>
> On 15 October 2015 at 23:35, Damien George <damien.p.george at gmail.com>
> wrote:
>>
>> Wow, that TI-82 tracker is beautiful!
>>
>> I actually did try to play proper audio samples using the microbit
>> right at the start of all this music module stuff (as Michael says,
>> it's entirely possible).  But, the problem is you need an external low
>> pass filter and amplifier for it work.  You use PWM at a very high
>> frequency (say 1MHz) and then change the duty cycle to match the
>> current sample, samples which are output at the sampling rate, say
>> 8kHz.  Coupled with an external low pass filter, this gives a proper
>> analog output.  So that means you can play an arbitrary sound.
>>
>> You can use a capacitor and resistor to make a low pass filter.  But
>> then there isn't enough power left to drive a speaker, so you need an
>> active amplifier (or use headphones).
>>
>> Since this scheme required more external hardware than most students
>> would be comfortable with, I abandoned the idea.
>>
>> I think currently the music stuff is pretty cool, and accessible: any
>> old speaker will work and give you a decent volume.
>>
>> But, of course, always room for improvement!
>>
>>
>> On Thu, Oct 15, 2015 at 11:10 PM, Michael <sparks.m at gmail.com> wrote:
>> > It's possible. The micro:bit as it stands now is much more capable than
>> > the
>> > prototype device that I built. However the prototype I built was built
>> > around the Atmel 32u4 for the simple reason that it's a very similar to
>> > the
>> > Atmel 328P. The reason I mention that is because for that I created a
>> > singing "cat piano" for my daughter a few years ago. That used PCM
>> > encoded
>> > WAV files - one per key, hard coded in program data. The wav files were
>> > 8Khz
>> > 8bit mono files, which then output to a speaker.
>> >
>> > I reused the same technique to make a Harry Potter sorting hat for a
>> > Harry
>> > Potter themed birthday party later the same year. Videos of these things
>> > aren't online for personal reasons.
>> >
>> > I don't have the time at this instant to rewrite these for micro:bit,
>> > and
>> > haven't raised these previously because I didn't want to derail the
>> > really
>> > cool stuff going on here.
>> >
>> > (This list will go public at some point, so I don't really want to post
>> > a
>> > link to the video for the cat piano here, but happy to send it directly
>> > to
>> > those curious)
>> >
>> > In case it's useful to anyone, I've pushed the code for the cat piano
>> > here:
>> >
>> > https://github.com/sparkslabs/catastrophene
>> >
>> > The code for the harry potter sorting hat is here:
>> >
>> > https://github.com/sparkslabs/sortinghat
>> >
>> > If useful, cool. If useful just as inspiration for *later* (and I really
>> > would suggest *later* :o), that's cool.
>> >
>> > It's worth noting that it should be possible to directly drive a
>> > composite
>> > video display as well, since that's possible to do with the Atmel 32C4
>> > which
>> > is again lower power than we have available for the micro:bit.
>> >
>> > All that said though, on the Computing At School forums I saw the
>> > following
>> > query today:
>> >
>> >> The game could do with having sound effects. Anyone know
>> >> of an easy way to attach a small speaker to a Micro:bit and
>> >> generate sound effects? The only thing I’ve seen so far is the
>> >> Kitronik “Don’t Steal My Micro:bit Alarm” project which uses a
>> >> buzzer with simple ‘on’ or ‘off’ control.
>> >
>> > When micropython gets out there, people are going to be excited by
>> > what's
>> > already working here. (I know I am :-) )
>> >
>> > We don't need to make it perfect immediately, just leave the door open
>> > to
>> > the possible.
>> >
>> > For example, in Star Trek 2, when just before Spock goes into the engine
>> > room, Leonard Nimoy was asked by the director Nick Meyer to say
>> > "Remember"
>> > in a mind meld fashion to DeForest Kelley (McCoy). (I'm carefully
>> > avoiding
>> > spoilers for those who haven't seen these things :-) )
>> >
>> > That wasn't actually in the script, but Nick Meyer had done enough TV to
>> > understand how to add a place where a wedge could be placed to open new
>> > doors. Likewise, I don't think we need to worry about bit banging wav
>> > files
>> > at this stage or implementing polyphony, but leaving the door open,
>> > that's
>> > cool.
>> >
>> >
>> > Michael.
>> >
>> > On 15 October 2015 at 22:03, Nicholas H.Tollervey <ntoll at ntoll.org>
>> > wrote:
>> >>
>> >> On 15/10/15 20:02, Larry Hastings wrote:
>> >> >
>> >> >
>> >> > This guy wrote a simple MOD tracker for the TI 82 calculator:
>> >> >
>> >> >     https://www.youtube.com/watch?v=I6G0CnBSWVk
>> >> >
>> >> > I'll save you a trip to Wikipedia: that's got a 6Mhz Z80, an 8-bit
>> >> > processor.  And he's getting /four/ voices out of it, not to mention
>> >> > effects.
>> >> >
>> >> > Gentlemen, our monophonic bleeping and blooping just got TOLD.
>> >> >
>> >> >
>> >> > Anybody know an audio rendering specialist?
>> >> >
>> >>
>> >> That thud you heard in the distance... that was my jaw hitting the
>> >> floor.
>> >>
>> >> ZOMG etc... :-)
>> >>
>> >> Nice find Larry, nice find..! I wonder if/how this is possible on the
>> >> micro:bit...
>> >>
>> >>
>> >>
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