Altair 8800 - Circuit for Music System not working for me.

[Antonio Tamairón]

Hello.

I try to assembly the music system circuito connected to INTR pin (Arduino Due) but nothing occurs.

I have tested that INTR pin is between 0 to 1.2v when SALLY.HEX is playing after signal be inyected to the RC filter proposed in the documentation. Is correct?

Is there an alternative sound circuit? I thnik that the output voltage is very low.

Thanks in advanced.

[Chris Davis]

It is a line-level output.  Are you using an amplified speaker? 

BTW, for anyone else replying: he has built his own Altair 8800 emulator, not from a kit.

Antonio, you might want to mention that in your posts, as this group is mostly people that have built from a kit.

[Antonio Tamairón]

Ok.

This group is refered in the GitHub of David Hansel and I thought that someone assembled DIY version of Altair 8800. Sorry.

Yes, I'm using a amplied speaker, typical 90's PC speakers with 100W RMS.

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[Chris Davis]

Don't get me wrong, it's completely ok that you're here, yes there are a few here that built the project from David's instructions.  You just might want to mention you built this DIY without a kit on new posts, otherwise you're going to get a lot of answers assuming you have the kit version which may not be useful for you.

[Chris Davis]

Back to your question about the Pertec Music System -  it's pretty foolproof, just one resistor and two capacitors.  The ACUTER software is not very user-friendly, so make sure you're following David's instructions exactly.

[Antonio Tamairón]

Ok. Thank you so much Chris, I take your suggestion into account.

To view this discussion visit https://groups.google.com/d/msgid/altair-duino/5459693c-b940-4e6e-9329-c19e9f6c0e1cn%40googlegroups.com.

[Antonio Tamairón]

Yes, about Acuter all was ok, even INTR led blinks when I put PLAY command in the console.

To view this discussion visit https://groups.google.com/d/msgid/altair-duino/d0ef5c47-0b2f-40f3-b54f-c958a6eeacfen%40googlegroups.com.

[Chris Davis]

Darn, maybe David will chime in here soon.

[Antonio Tamairón]

These were my test.

- Connect in the led terminal - unsuccessful.

- Connect in the Arduino Due pin (before led driver) - unsuccessful

I have checked voltage in the INTR anode terminal, voltage is between 0 to 1.2v

To view this discussion visit https://groups.google.com/d/msgid/altair-duino/bc20576a-21b4-43e6-b9bb-9bde6806bb2fn%40googlegroups.com.

[da...@hansels.net]

Have you measured the signal on the actual audio connector where you plug in your speaker?

You should measure AC voltage. I can't test it here right now but the voltage should be somewhere

between 0 and 1 Volt (audio line level voltage). Ideally you should look at the signal on an oscilloscope

(if you have one) to see the actual levels.

Test the voltage _without_ the speaker plugged in first. If that looks good then test it with the speaker

plugged in. If the voltage drops to 0 when you plug in the speaker then there is a problem with the speaker

(either it's not amplified or broken).

David

[Antonio Tamairón]

I think that my RC circuit is wrong.

The signal is Vpp_max = 0.2v

To view this discussion visit https://groups.google.com/d/msgid/altair-duino/19923599-6f5b-4293-a69b-f234016eaddcn%40googlegroups.com.

[Antonio Tamairón]

Hi again.

I already solved the issue. I have connected directly the output of INTE drived pin to RCA audio connector, because if I use RC filter the output voltage is very slow maximun about 800mV. Now voltage is around 4v and sound very good!!!

I´m using UDN2981A to drive leds. This device has several channels and provide 5v without voltage dropdown.

Thanks so much.

Regards.

[Antonio Tamairón]

This solution of audio through INTE is only useable with Music System? I try to play with SW3-SW0 (1010) Musica 'Daisy' but I don't ear nothing.

[Chris Davis]

The audio jack is only for the Processor Technology Music System.  The code for Daisy demonstrates how the Altair was used to produce music on a nearby AM radio.

https://adwaterandstir.com/2017/05/30/play-daisy/

[da...@hansels.net]

Just for anybody who comes across this thread in the future: I made some measurements as to what would be the

expected signal and voltage level on the audio output. This was captured while playing "Lay down Sally" with the Music System.

This was captured while playing with just a basic pair of powered PC speakers. I set the volume knob on the speakers
to about 1/4 and had perfectly fine audio volume.

On an oscilloscope you should see short spikes of about 400-600 mV:

Zooming in a bit more the spikes look like this:

Since the spikes are very short, this does not show up as much on a Multimeter.

When measuring voltage in AC mode, I see between 10mV and 50mV when the music is playing.

As I said above, the music plays just fine with these levels using simple powered PC speakers.

David