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Ideas for what to do with an FM chip?
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Ideas for what to do with an FM chip?
äggmedskägg
So, I was in Tokyo, and in an electronics store they had this ball-type machine, where you insert a coin, twist a knob and out comes a ball with a random toy. But this random toy was second hand FM chips. (Getting them off old sound cards seem to be the only way to find these nowadays).

Obviously, I couldn't help myself and ended up with a YM3824 chip! Cool.

But what should I do with it? Sure, I can in theory connect it up to some controller and program it from the computer over USB or something. But what fun is THAT? I already have a Yamaha TX7.

Does anybody know more about how these work? Could I, for example, program it by stuffing semi-random data in it, and use it as a semi-random noise-box? That would be pretty damn cool. But I'm WAAAAY out of my depth here.

Ideas of how to do that, or well, anything else really, are very welcome. Off the wall is good, simple is good.
Ayab
Here is the data sheet that has some description but I am not familiar with most of the terminology:

https://www.datasheet.live/index.php?title=Special:PdfViewer&url=https %3A%2F%2Fpdf.datasheet.live%2Fdb0d4e1d%2Ftoko.com%2FYMZ280B-F.pdf
nrrrd
Have a look at Akemie's Castle by ALM Busy Circuits:

http://busycircuits.com/alm011/

I'm not necessarily suggesting you build a Eurorack module, though! smile

I'd try to build a self-contained instrument, controlled by an Arduino or Teensy, but with some analog modulation sources and maybe an analog filter on the combined output.

Think Ciat-Lonbarde, or Lorre-Mill, or Hordjik's Benjolin but using an FM chip and micro-controlled.

Mmmm, you've got me thinking now. To eBay!
jorg
Ayab wrote:
Here is the data sheet that has some description but I am not familiar with most of the terminology:

https://www.datasheet.live/index.php?title=Special:PdfViewer&url=https %3A%2F%2Fpdf.datasheet.live%2Fdb0d4e1d%2Ftoko.com%2FYMZ280B-F.pdf


That's a different part.
joem
Some of those old Yamaha FM chips needed another chip to work right... I really can't remember what or why, though. (Some kind of amplifier, maybe?) Anyway, if this one is one of those Yamaha ones, you're going to want to hunt down that companion chip.

You'll definitely want to find a datasheet, otherwise you won't be able to do much of anything. I think most/all of those Yamaha chips take their data in digitally instead of analog, so without a datasheet you won't know the protocols or the pins.

I like the idea of feeding it semi-random data. I picked up some old FM chips (I think they were OPL2?) once with the intent of doing something similar, but by the time the chips arrived I had moved on to something else. Maybe I'll revisit that sometime.
commodorejohn
joem wrote:
Some of those old Yamaha FM chips needed another chip to work right... I really can't remember what or why, though. (Some kind of amplifier, maybe?) Anyway, if this one is one of those Yamaha ones, you're going to want to hunt down that companion chip.

That'd be the DAC. I think there's a list out there somewhere of which FM chips require which specific Yamaha DACs; I think some of the more integrated-sound-solution ones do it onboard, but I can't recall.

The thing I've long wanted to do with old Yamaha chips is take one of the 2-op ones and build a proper knobby early-'80s-style poly out of it. But that's gonna have to wait until I've brushed up on low-level electronics a good deal...
ranix
äggmedskägg wrote:

Does anybody know more about how these work? Could I, for example, program it by stuffing semi-random data in it, and use it as a semi-random noise-box? That would be pretty damn cool. But I'm WAAAAY out of my depth here.

Ideas of how to do that, or well, anything else really, are very welcome. Off the wall is good, simple is good.


The YM series chips that I've used have a parallel data bus and a parallel bank select bus. You twiddle your data pins to select which register you want to modify, then twiddle your bank select, then twiddle the data pins a second time to set the data in the previously-selected register to the bus value.

The later YM chips are more advanced, have more features, and may separate the data bus into two busses so you can clock in your register address over a different line than your register content and get the job done faster. I don't think all the YM chips are FM, some of them might be PCM.

joem wrote:
Some of those old Yamaha FM chips needed another chip to work right... I really can't remember what or why, though. (Some kind of amplifier, maybe?) Anyway, if this one is one of those Yamaha ones, you're going to want to hunt down that companion chip.


iirc this did have something to do with a DAC but something in my long term memory is making me want to call this chip an "accumulator"

I don't remember this very well but I think some YM-series chips had this accumulator chip to mix the outputs of all FM operators together, but other YM-series chips time-domain multiplexed the outputs instead of using the accumulator. I believe but am not certain the YM2612 and YM3438 are examples of YM series of chips that use time-domain multiplexing instead of an accumulator.
äggmedskägg
nrrrd wrote:
Have a look at Akemie's Castle by ALM Busy Circuits:


Hmmm. What would actually be helpful there would be the circuits. :-)

But, this does help in one way: I might be able to simplify things by just using this as an oscillator. Only change things like frequency, level and algorithm.

Hmmm...
äggmedskägg
ranix wrote:
The YM series chips that I've used have a parallel data bus and a parallel bank select bus. You twiddle your data pins to select which register you want to modify, then twiddle your bank select, then twiddle the data pins a second time to set the data in the previously-selected register to the bus value.


Right. And I was thinking I could maybe somehow do that without an arduino or whatever. Now I'm thinking probably not. :-) Not if I actually want it to make any sort of useful noise, I suspect.

Ah well, I have some other projects I need to do first.
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