The Tandy 1000 ISA sound card brainstorm thread.

Discussion about old PC hardware.

Re: The Tandy 1000 ISA sound card brainstorm thread.

Postby carlostex » 2016-12-12 @ 12:30

I would advise everyone to wait for a rev 2 board, unless you're in a super hurry.

I'll probably sell one of my rev 1 boards though, i have no need for 2 early boards. :happy:
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Re: The Tandy 1000 ISA sound card brainstorm thread.

Postby Scali » 2016-12-12 @ 12:51

carlostex wrote:I would advise everyone to wait for a rev 2 board, unless you're in a super hurry.


Yes, the current board works, as a proof-of-concept. We still have two issues to iron out though:
1) The PC speaker input suffers from high-pitched noise.
2) We're not entirely sure if the current C0h, 1E0h and 2C0h addresses are the best possible choice. Especially the 2C0h one (that was our 'AT compatibility' option, since C0h is taken there, and 1E0h is in a 'reserved range'. C0h is the default for PCjr and early Tandy, and 1E0h is used for later AT-class Tandy machines). We're looking into replacing it with an address in the 00h-FFh range, so that code using C0h can easily be patched in-place. We will probably want to go for port E0h.
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Re: The Tandy 1000 ISA sound card brainstorm thread.

Postby Jo22 » 2016-12-13 @ 02:33

Hello everyone, please forgive me for crashing in into this wonderful thread,
but just recently I've seen something loosely related to the thread's topic.
I've seen a page where someone made a Tandy Sound clone and a hardcore SB replica using TTL chips(!)
The page is here, it also has some wiring diagrams and code for the Tandy emulator.
I thought this could be helpful to improve this wonderful project..
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In what to one race is no time at all, another race can rise and fall..." - The Minstrel

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Re: The Tandy 1000 ISA sound card brainstorm thread.

Postby bjt » 2016-12-13 @ 15:39

Scali wrote:Yes, the current board works, as a proof-of-concept. We still have two issues to iron out though:
1) The PC speaker input suffers from high-pitched noise.


I observed the same issue when connecting a 5160 PC speaker output to a SB Pro 2.
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Re: The Tandy 1000 ISA sound card brainstorm thread.

Postby keenerb » 2016-12-13 @ 15:45

I actually think the 10k adjustable resistor on the pc-speaker input is muting the volume too much; I'm turning up the volume on my external amplified speakers much higher than I'd normally expect and it's magnifying the normal EMI noise you get on these old systems.

That's my guess anyway. When I run the PC-Speaker input through pin 9 on an SN76496 it's really loud and clear with no observable background hiss, but oddly any connection to PIN 9 mutes the tandy 3-voice audio...
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Re: The Tandy 1000 ISA sound card brainstorm thread.

Postby Scali » 2016-12-13 @ 15:46

bjt wrote:I observed the same issue when connecting a 5160 PC speaker output to a SB Pro 2.


I didn't...
These two captures were both done from a 5160 (two different machines), and an SB Pro 2:
https://youtu.be/yHXx3orN35Y
https://youtu.be/uZ6LcSv3NH4
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Re: The Tandy 1000 ISA sound card brainstorm thread.

Postby pearce_jj » 2016-12-15 @ 19:30

Hi All, sorry I've not been following this thread (only the vcfed one).

The issue with the input is that the PC speaker uses an open-collector drive. The level can be bought up to where it should be by adding a pull-up on the speaker audio input, something like 30 ohms or so. Hopefully that will also resolve any noise/hiss issue.
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Re: The Tandy 1000 ISA sound card brainstorm thread.

Postby j^aws » 2016-12-15 @ 19:50

^^ Some great work by all involved. Do you have any idea when we'll see a revised version of this board?
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Re: The Tandy 1000 ISA sound card brainstorm thread.

Postby Scali » 2016-12-15 @ 23:20

I've just completed mine, and it works like a charm: https://youtu.be/jb2kt4t0Xv4
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Re: The Tandy 1000 ISA sound card brainstorm thread.

Postby matze79 » 2017-6-19 @ 08:55

Hi,

i now think i'm waited long enough for the pcb to finish, and since few months there is no progress.
i really want to own a tandy soundcard.
Can you point me into right direction ?

is the R01 Schematic inside this Thread the same used for the current pcb ?
https://www.lo-tech.co.uk/wiki/Tandy_Sound_Adapter


i got all necessary stuff including Prototype ISA Card for testing purposes.
Maybe someone can point me to right direction.
Or even has a PCB left ?
And can scan backside and front?

Thanks for help
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Re: The Tandy 1000 ISA sound card brainstorm thread.

Postby Scali » 2017-6-19 @ 09:16

I believe the redesign for the Rev 2 board got stuck on the design of a decent mute-circuit at bootup.
As you may know (and is obvious from my video), the SN76489 will start up in a non-silent state (doesn't seem to be random). A real Tandy/PCjr will set the volume of all channels to 0 during BIOS POST to work around this issue.
We do not have that option, so you hear an annoying tone from the moment you power on the machine until you get it booted up and can run a utility to shut it up.

We have yet to find a way that is robust and not too expensive/complex to implement, to get around this.
Ideally, there would be a hardware mute circuit (eg some relay), that cuts the circuit somewhere (eg cut the power to the amp). Ideally it would switch on automatically when a command is written to the card. And back off again when you reset the machine (I suppose during a warm reboot, the card will remain silent, so we do not have to solve that case).

Mind you, I personally could live with just having the volume control moved to the back of the card.
That way I could just dial the volume all the way down when I start up the machine.
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Re: The Tandy 1000 ISA sound card brainstorm thread.

Postby matze79 » 2017-6-19 @ 09:38

what about using a small mcu that does that on sn76489 ?
a dip16 mcu should be fine.
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Re: The Tandy 1000 ISA sound card brainstorm thread.

Postby Great Hierophant » 2017-6-19 @ 13:54

I suppose a BIOS extension ROM would be like killing a fly with a sledgehammer. Otherwise, a simple Tandy mute program would work for DOS booting. But it won't work for PC booters, especially if they only use one or two of the sound channels.
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Re: The Tandy 1000 ISA sound card brainstorm thread.

Postby Scali » 2017-6-19 @ 14:29

Great Hierophant wrote:I suppose a BIOS extension ROM would be like killing a fly with a sledgehammer.


Not only that, but you don't know when exactly the extension ROM will be called.
Chances are it will be called after the initial diagnostics and memory test, in which case you're still listening to the beeping for a considerable amount of time.

I guess an externally accessible volume knob is the simplest and cheapest way to deal with this (or perhaps an externally accessible mute-switch, so you can leave the volume in the preferred setting, and just enable/disable audio quickly).

I think there's a workaround for the booters, I see two possibilities:
1) First boot to DOS, run the program to mute the entire chip, do a warm boot to load the booter. Unless your BIOS writes to port C0h (I think my Philips does that, because I can hear the pitch change during bootup, doesn't happen on my 5160), the card should stay muted during the warm boot.
2) Create a simple utility that can load a booter directly from DOS, so you don't have to reboot the machine at all.
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Re: The Tandy 1000 ISA sound card brainstorm thread.

Postby Great Hierophant » 2017-6-19 @ 16:35

Some computers can boot to DOS pretty quickly like my 486 and my Tandy TL. Other computers can take an agonizingly long time to boot anything, like an IBM PC 5150. How difficult would it be to program and integrate a microcontroller to send the four bytes to the chip necessary to mute the volume?
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Re: The Tandy 1000 ISA sound card brainstorm thread.

Postby Scali » 2017-6-19 @ 17:10

Great Hierophant wrote:How difficult would it be to program and integrate a microcontroller to send the four bytes to the chip necessary to mute the volume?


I think the biggest problem is designing the circuit so that both the microcontroller and the ISA port can write to the SN76489. I don't think you can just connect both data lines to the SN76489 directly and just expect things to work.
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Re: The Tandy 1000 ISA sound card brainstorm thread.

Postby keenerb » 2017-6-19 @ 20:02

Scali wrote:
Great Hierophant wrote:How difficult would it be to program and integrate a microcontroller to send the four bytes to the chip necessary to mute the volume?


I think the biggest problem is designing the circuit so that both the microcontroller and the ISA port can write to the SN76489. I don't think you can just connect both data lines to the SN76489 directly and just expect things to work.


I thought about this for a litle while; you'd have to use the microcontroller to trigger some of the ISA bus controls, right, which means it might screw with the ISA bus itself and cause a boot hang or undesired behavior.

Could you use a diode to filter that out?
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Re: The Tandy 1000 ISA sound card brainstorm thread.

Postby Jepael » 2017-6-19 @ 21:32

I don't think the microcontroller would work so well. Except maybe if all sound chip pins are multiplexed to the separate MCU. The hard part is not to code the program, but determine how to mux those pins (few more chips) and how to write the program into MCU flash in the first place (OK, modern ones even have UART bootloaders). But it still has to know when to init the sound chip to silence, like on ISA bus reset signal, and to mux those pins back to ISA bus.

Another solution would be to use the reset pin on ISA bus to just cut audio on cold boots (somehow, like relay, analog mux or whatever). Then, writing some port could activate the output again. Or reading a port enough times. This could be made with an init tool in autoexec.bat, to init the chip before enabling sound output.
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Re: The Tandy 1000 ISA sound card brainstorm thread.

Postby matze79 » 2017-6-23 @ 13:03

I think the biggest problem is designing the circuit so that both the microcontroller and the ISA port can write to the SN76489. I don't think you can just connect both data lines to the SN76489 directly and just expect things to work.


Hm just use a Busdriver and connect it beetween ISA Bus and SN76489
Connect datalines of SN Soundchip directly to Busdriver and to MCU.
MCU executes its Program, enables Busdriver.
PC takes over.

This will work in few ms :O
The MCU Program is rather simple i think just 3-5 lines of code.

EDIT:
https://github.com/skywodd/avr_vgm_play ... 76489_test
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Re: The Tandy 1000 ISA sound card brainstorm thread.

Postby Scali » 2017-6-23 @ 13:18

matze79 wrote:
I think the biggest problem is designing the circuit so that both the microcontroller and the ISA port can write to the SN76489. I don't think you can just connect both data lines to the SN76489 directly and just expect things to work.


Hm just use a Busdriver and connect it beetween ISA Bus and SN76489
Connect datalines of SN Soundchip directly to Busdriver and to MCU.
MCU executes its Program, enables Busdriver.
PC takes over.

This will work in few ms :O
The MCU Program is rather simple i think just 3-5 lines of code.

EDIT:
https://github.com/skywodd/avr_vgm_play ... 76489_test


Well, if you think you can make it work, and also keep the cost and complexity down (the idea is that this card will be affordable and easy to build from scratch, much like eg the XT-IDE cards), perhaps you can suggest it in the 'main' development thread of this card, over at vcfed: http://www.vcfed.org/forum/showthread.p ... atible-PCB
I'm not sure if pearce_jj actively monitors this thread.
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