This is not the most original project; many people have come up with
the idea "what if I hook my embedded board to 1980s vintage
sound chips."
I started going down this road when working on my
Apple II KSP project got me thinking about
ancient sound cards, specifically the Mockingboard Sound available
on old Apple IIs.
These boards used the AY-3-8910/1/2 sound chips, which can generate
3 channels of square waves with other effects. They were commonly
used in some Spectrum and Atari computers, among other places.
There is/was quite a scene about generating chiptunes for these chips.
So I ended up spending a lot of time on this project:
a Raspberry Pi playing YM chiptune files on actual AY-3-8910
hardware, with LED visualization.
The AY-3-8910 is fairly straightforward.
Three channels of square waves plus various noise and envelope effects.
Provide a clock (1MHz in our case)
and there are 16 (well, 14) on-chip registers you write to.
Just put the address then the 8 bit value
on the bus, toggle the 3 bus control pins, and you are set.
You'll want to do this fairly fast.
A typical YM music file wants you to write all 14 registers every 50Hz.
In order to save GPIOs I use 74HC595 shift registers driven by SPI.
I drive the AY-3-8910 control bus with additional GPIOs.
Visualization is done with some i2c LED displays.
The amplifier originally was an LM386 design from Figure 16 of the
AY-3-8910 datasheet.
I currently am using an Adafruit MAX98306 breakout instead.
It is currently driven by a Pi-2. I tried a Pi-B+ but with only
a single core there was too much jitter (possibly caused by the
Operating System). I have not tried a Pi-3, I am not sure how
the thermal issues would play out.
Yes it is depressing that a modern overpowered ARM board can't keep
up in real time with an old Apple II
(see the
French Touch "Pure Noise" Demo). I plan to modify
my bare-metal
operating system so it can drive the board, hopefully with less overhead
than Linux can provide.
Features
Dual AY-3-8910 for 6-channel stereo sound
i2c display including 8x16 display, 6 bargraphs,
12 characters, and 8 buttons
i2c real-time-clock so it can be used as an alarm clock
1-wire temperature sensor
Dual 4W speakers, can also output to stereo 3.5mm jack
Currently to access the features you connect via ethernet and do things
from the Linux command line.
Ideally the software will be such that it boots up and into a menu
system, and using only the buttons you can navigate and access all the
features. Also you could do things like plug in a USB key with .YM5
files on it, and it will automatically start up the player and start
playing them.
Build Log
22 May 2019
I've added code so the player can now play unmodified Vortex Tracker II
.PT3 files. This was all part of the work to do the same on
the Apple II. I even added support
for 6-Channel .pt3 files.
18 October 2017
The music being played was occasionally glitchy. I had written that
off to the Pi/Linux not being real-time, but after some e-mails from
someone building their own player I realized I was only driving the SPI
bus at 60kHz. (Probably because I was initially testing on a breadboard).
The board seems to work the whole way up to 64MHz SPI but that seems a bit
high. I'm now running at 15MHz (as that should be in spec for the shift
registers), let's see if it sounds any better.
8 September 2017
So why build one when you can have two for twice the cost:
25 August 2017
Have most of a second device together. Updated the manual to fix
things I left out.
9 June 2017
Finally get the demo movie together. About time, as there are other
things I'm supposed to be getting done this week. See if you can
spot the typo in the movie, I don't have time to fix it right now.
6 June 2017
Finally got "Still Alive" recorded. It was a lot of work and turned
out more or less OK.
1 June 2017
The hardware is mostly done, work on finishing up the writeup as well
as working on the software.
Working on the still alive video. The ym5 file I tracked myseful was
too boring sounding, so I'm writing a xm to ym5 converter so I can
play the more chiptuney version. Also working on a custom file format
so I can play 6-channel audio.
21 May 2017
Was drilling holes in the case.
Should probably invest in some more modern tools.
15 May 2017
Finally got a chance to post a video of the soldered together board.
I had a student using the Pi2 for a final project so I couldn't connect
it to the chiptune player. I tried using a Pi-B+ but it turns out that
sadly it can't keep up, at least with the current code you need a Pi2
(more for the extra core to handle OS stuff rather than speed I think).
I really should write a bare metal version of the player software.
It's embarassing that a modern day system can't keep up with a 40 year
old 6502 implementation.
10 May 2017
Connected the display board to the sound board.
The hardest part was making the connectors to attach the speaker
and i2c cables.
8 May 2017
The PCBs finally arrived! Finally had time to put the sound board together.
Here's the front and back mostly assembled but not yet populated.
Alarmingly one of the 74HC595s got really hot when doing bringup testing.
It seems like that particular chip had issues, as a replacement one was fine.
So aside from a few clearance issues (the oscillator in particular) the boards
are more or less just fine.
Here's the fully assembled board playing some music:
I'm still not 100% happy with the sound quality though :( Need to hook up the
scope and figure out if it's something inherent in the chips, or just something
stupid in my design. I am following the the reference design in the datasheet though,
and even though a Class-D amp might not be the best idea for amplifying square waves,
the raw audio from line-out sounds about the same. I'm a lot better at digital
design than analog.
22 April 2017
Sent off the PCB, now just waiting for it to come back...
21 April 2017
Here's a picture of the final prototype, including the slider subassembly,
an amp cutoff switch, and the real-time clock. It all checks out, so
hopefully the PCB matches. I'm adding a ground fill, which I've never
done before, so hopefully it all works. I also gave up on trying
to autodetect the status of the headphone/line-out jack,
ran into lots of complications with that.
14 April 2017
Have the PCB for the sound board about 75% done then realized I had
put the Pi-2 flush against the corner where a mounting screw would be
in the way. Had to move everything over 300mils. Need to find time
to finish this.
22 March 2017
Got the volume control on the max98306 working using GPIOs.
The 74AHCT125N chips work wonders, though I'm wasting a lot of gates
as I don't have a nice even amount of signals.
Next up is seeing if I can sort out the headphone issues.
21 March 2017
Finally got SPI working! 8ms latency (versus 14ms when bitbanging)!
Level shifters made all the difference.
Here's a picture of me debugging the issue with LEDs before reconfiguring
the shift registers to use SPI.
20 March 2017
I was doing some timing.
To hit 50Hz you can't have more than 20ms of latency each frame.
Adding the 3 additional i2c displays (14-seg alphanum) pushes it up
to 21ms. So time to see if I can get SPI going for good, as that's much
faster than bitbanging the shift registers like I'm doing now.
The parts order finally escaped from New Jersey, which is good, because
they contain the key to getting
SPI working (at least with LEDs).
The problem seems to have been that the 3.3V inputs weren't
consistently high enough to drive the 5V serial/parallel latch.
And the level converter I was trying to use was optimized for i2c
and somehow wasn't working right. A more boring 74AHCT125 seems to
be working.
17 March 2017
More or less have the display part working. A demo of it in action:
I need to get some shades for that window, makes it hard to see the display.
Now I need to see if I can get the audio board working. Still having
problems with hum, dropouts, headphone detection, high-Z inputs. Analog
is so much harder than digital!
13 March 2017
The purple package finally arrived!
Assembling the board wasn't too bad. Most of the problem was various
holes not being aligned properly, but nothing disastrous.
And it even worked, first try! Not bad. I need to get a better setup
where I can take pictures without glare. The LEDs are so bright they
confuse the camera a bit and having a big window behind things doesn't
help.
Now to get back to debugging the analog side of things.
10 March 2017
I spoke too soon. Never solder things unless they work in a breadboard
first. The level shifter was floating high when the Pi was trying to
do high-Z (which makes sense as it's an i2c optimized level shifter).
I tried dropping the supply to 3.3V to avoid the shifter.
I somehow thought the Pi GPIOs went high impedance when put
into "in" mode, but apparently not high impedance enough, as both the
headphone detect and gain select were leaking enough current that things
weren't working.
Frustrating. Also the 4 Ohm resistors don't sound as nice as the 8 Ohm
resistors. And the filter caps add both pops and hum, which is odd
because they should be a low-pass filter.
Also the headphone jack isn't working with the filter caps on.
Anyway I ordered some different level shift hardware to see if I can
at least get the gain/jack detect working. The package is currently
trapped in New Jersey by a blizzard though.
8 March 2017
The PCB for the display board was finally sent off to be made, now it's
just a matter of waiting for the purple package from OSH Park.
In the meantime I've been working on the sound board. I've even put together
this prototype board that in theory allows software headphone jack detection
as well as software volume control (all level shifted down to 3.3V for
Pi GPIO). Time to hook it up and see if any magic smoke escapes.
22 February 2017
I've been sidetracked on writing code that does the "Still Alive" demo,
with synchronized lyrics. The idea is I can have one chunk of code
that will create a Pi-chiptune Demo, as well as one that can
target my Apple II code.
Here's Chell watching as I test things out. I need some way to block
glare when taking these pictures so the LEDs show up better (my
office window
doesn't have blinds for some reason.)
Also made some art for the 16x8 display. Getting recognizable shapes
in one color is a challenge.
Currently I need to get another Red 14 seg display (looks a bit odd
with that blue one), finish the ym5 chiptune, find some way to get SPI
to work, and then get line-out audio going so I can record without having
all the background noise interfering.
4 February 2017
Still working on things, have been sidetracked trying to write my own
ym5 files to play on the device. Learning a lot about synth envelopes,
ended up almost writing a tracker.
30 September 2016
Further trying to track down why SPI to 74hc595 isn't working for me.
Hooked up a sample driving LEDs and put it on an oscilloscope and
the waveforms from the Pi look perfect. Yet the actual LEDs that
get lit up do not match the signal sent out. Frustrating.
29 September 2016
Tried driving things with SPI rather than GPIO. In theory this should
offload a lot of the bit-twiddling and potentially improve the sound
a bit. Sadly I just could not get this to work. Mysteriously, even
trying to bitbang the SPI GPIOs directly didn't work.
28 September 2016
Improved the player, now looping works.
27 September 2016
Worked on the player. Can now also play YM2, YM3, YM3b and (in theory)
YM4 files. You can also now specify more than one file on the command
line and skip through them using the keypad.
26 September 2016
Use libhasa to decompress YM files, now you no longer have to do
this manually.
23 September 2016
Added a headphone/line-out jack. It is the type with built in switches
to automatically cut off the speakers when a plug is inserted. However
the amp doesn't like floating inputs. I couldn't find the type of jack
with an independent switch that I could have run to a GPIO and cut off
things in software. I'll have to think about the best way to handle
this.
22 September 2016
Worked on improving the 8x16 display. Some new features, and the buttons
now work.
15 September 2016
Cleaned up the ym_play code a lot. It's almost presentable now.
Now there's a hope that if you build a device like this you can
use ym_play and get it working.
It would be nice if people let me know things like this. I noticed my
youtube views had suddenly doubled overnight so I had to do a google search
to find out why.
I admit most of the popularity credit should go to Aleksy Lutsenko's
awesome music (I admit it's the whole reason I started this project).
All I did was hook up a few wires on a breadboard. I doubt this project
would be anywhere near as popular if I had put together a one-channel demo of
Twinkle Twinkle Little Star.
Also, disgruntled Atari and Spectrum users, I do realize that most of
the cool music comes from your scene. I only mention the Apple II
Mockingboard because I actually had a neighbor who had one. For me
growing up
Spectrum and Atari computers were mythical things that only appeared
next to BASIC video game listings saying "to make things work on your
ZX81 Spectrum please make these changes".
13 September 2016
Working on getting the 8x16 display able to print things other
than just the waterfall display.
Have time played indicator working.
Need to put out a new video with the new features.
9 September 2016
Have dual AY-3-8910 working. Stereo!
Of course I don't have any 6-channel music files so I'm just
duplicating the 3-channels out both speakers.
6 September 2016
Moved from LM386 amp to an Adafruit MAX98306 breakout.
The output of the AY-3-8910 is too high to hook directly, you need
to put a voltage divider across the output.
Also tweaked the shifter delays, and now we auto-delay the proper amount.
Now we're having no problems hitting 50Hz consistently.
Also worked on the waterfall display. A bit nicer. Was trying to make
it logarithmic but that didn't really work very well.
4 September 2016
Article on this project posted on
Hackaday.
The video was possibly also trending on Youtube somehow.
2 September 2016
Have sound and LEDs going!
Here's the above, annotated:
1 September 2016
Fixed issues with sound (off by one error, loose address wires).
Working on the visualization.
Also dropped down to a 1MHz clock, as at 2MHz upsampling 1MHz and 1.7MHz
YM files was causing overflows.
30 August 2016
First sound with this setup! Still some issues though
29 August 2016
Testing to see if I can use a 74HC595 shift register.
Simple test getting output on LEDs worked great (once I figured out
upstream Linux [yes I am running 4.8-rc3 on my pi2] wants you to add 970
to the GPIO number).
26 August 2016
Final batch of parts arrived!
25 August 2016
Wrote some code to decode YM file format.
The LHA compression and the interlaced format is a bit of a pain.
