SwinSID SE - reworked by Me

Been toying with the SwinSID which is a decent DIY version of the SID chip. My version takes up no more space than the original and would be a drop-in-replacement with no extra wiring. Programming the atmega would be a little difficult though since there is no room for an ICSP.

Miracle Piano Final Thougts

I finally had time to probe a few pins inside the Miracle Piano.

AS0012 - Pin 21 (PWM)
It turns out this pin controls the master volume and NOT the envelope as I had originally assumed.
Turning on the keyboard, this pin defaults to about 50%, but as you can see, it is not exactly 50%. How odd.
When the volume is reduced, the pulse width is widened and when the volume is increased, the pulse width is reduced. That is because the integrator, U4A is inverting the output.

Each photo has the scope set to 10 microseconds per division:

Default Volume:



Highest Volume:



Lowest volume:



U4 - Pin 1
This pin goes to the LM13700 to control the master volume, or gain of the sound. It appears as a DC voltage and is remarkably solid. There is no visible ripple as would be expected from an integrator.
No photo is needed of this signal.

J004 - Pins 21-24 (OUT1-OUT4)
The signals from these pins are too small to view on my scope, so I chose the amplified versions from U10. Pins 1, 8, 7 and 14 respectively.

OUT1 is not active for all sound samples, apparently. When Harpsichord and Synthesizer are selected, nothing comes out at all.
When the other four sounds are selected however, the waveform is perfectly clear.

OUT2 is the opposite. Only when Harpsichord and Synth are selected, do we see any activity on this pin.

OUT3 mimics OUT1 exactly, or at least as far as I can tell.

OUT4 on the other hand does not seem to react to any button or key. It simply outputs a DC voltage which measures 5.03v at pin 14 of U10.

I can speculate as to why there are three OUT pins. While probing both Pins 8 and 14 of U4 which has the mixed and filtered outputs split to both left and right output terminals, the waveforms are identical for Harpsichord and Synthesizer but are not identical for the other four sounds. It would seem that Harpsichord and Synthesizer were recorded and digitized in mono while the other four sounds were recorded and digitized in stereo.

I am a little saddened that the envelope is not broken out to any specific pin or sub-circuit.

Some other Notes

J004 - Pin 40 (Bus Strobe)
This pin reacts differently for different sounds, however, when the key is pressed with a sound that has an attack and release; the pin will strobe for the full length of the sound and go to 0 when the note is finished.
For a sound that ends only when the key is released, the pin strobes at key press for a moment, then goes to 0 and strobes once again when the note is released.

I could use this pin for creating a gate and trigger, but it would require that I charge a capacitor then feed it through a comparator and set up some logic to keep the signal high when the key is pressed and low when the key is released. This wouldn't require too much effort, but the function would change from sample to sample since the envelopes are all different. I don't thin the modification is worth it in this case.

"Piano" sample is very hard to photograph since the amplitude changes so rapidly in software. It looks very similar to "Organ, but is more rounded whereas the Organ is more triangular.


"Organ:"



This photo shows a sample that is identical on both sound channels. Trust me, they are identical but the channels are not being displayed the same way.


These two photos show sounds that are not identical from OUT1 and OUT2.



PS: Yes, the reflection in my oscope is naked. Deal with it.

CCAM - Crystal Clear Audio Mod for Sega Genesis/MegaDrive by Tiido

I took an afternoon to look at Tiido's circuit to clean up and amplify certain channels on the poorer created versions of the Sega Genesis and megadrive. This circuit separates all of the audio channels, amplifies them individually, mixes, amplifies again, offsets the DC output and applies a low pass filter. This is based on the sound filter inside of the original "HD Graphics" models of the sega genesis which arguably has the best sounding output.

I have taken the liberty of redesigning the circuit with all higher quality 1% tolerant, through-hole components, a low power op amp and easy to solder tie points for installation.

Do not stay at the Guest Quarters Hotels - Dumping The Miracle Piano Teaching System

I had my Willem programmer pulled out for some Sega Genesis programming stuff and decided to finally dump the eprom inside of the Miracle Piano teaching System Keyboard. If you recall from a previous post of mine, it contained a 27c256 OTP eprom. It also contained many proprietary ICs of which I may never figure out. We may never know what microcontroller they used or what language the machine code is suppose to be written in. z80, 6502, etc.

In any case; with many vintage computers and other devices containing ROM, the authors always find the space to sign and date their work and in rare cases they may even decide to add a little easter egg. Although I cannot locate a date, here is some clear text I found in the ROM image:

"This Eprom contains code created by Mike Collins. Anne Graham and Ray Livingston. Do not stay at the Guest Quarters Hotels. Keep that Coke classic and that Piping hot coffee coming."



I got a real kick out of reading that. For anyone who knows what to do with it, here is the binary file:
http://www.mediafire.com/download/eo3zujca7jvw44f/MPTS_ROM.zip