|MITS Altair AM Radio Music Jukebox||by Bill Degnan - 05/07/2018 23:13|
MITS Altair "Jukebox" system with GE Radio on top. Click image for larger view.
MITS Altair "Jukebox" system exhibit at the 2018 Vintage Computer Festival. Click image for larger view.
Steve Dompier's May 1975 People's Computer Company newsletter article Music of a Sort (republished in Dr. Dobbs Feb 1976) describes how one would generate music with a MITS Altair by using the front panel to generate tones that could be received over an AM radio. The goal of this project is to experiment with ways to automate the use of this program by creating a "jukebox" interface that can be used from a period-appropriate terminal to play various musical selections.
Here is a photo of the front panel card, expertly repaired by Jon Chapman of Glitchworks, making this exhibit possible. Click image for larger view.
The DAJEN System Central Interface "SCI" controller. The DAJEN SCI is an all-purpose interface card compatible with most S-100 systems. The monitor commands are HEX based. I selected the DAJEN for the Altair Jukebox because its monitor program has a built-in RAM block move utility and because it's a change of pace from the other ROM monitors I have. I have also experimented with the MITS TURNMON and Vector Graphics ETKM ROM monitor programs. They all work about the same. The key role of the DAJEN is to move the music program and data stored in ROM at location 8000 to volatile RAM at 0000 for execution. Click image for larger view.
After assembling the hardware I created the Jukebox program in phases. First I downloaded Dompier's program into RAM in location 0000 - 00xx via the serial port and used the DAJEN SCI monitor to run the music program from the monitor prompt. To execute, the command is: "G 0000". Next I converted the program into HEX so that I could copy to a 1702A ePROM chip, thus to avoid having to download the program through the serial port each time. I generated additional tunes by converting the notes from selected sheet music into octal format per Dompier's article. Both the DAJEN and 1702 ePROM burner use HEX format so I converted the notes and program into HEX format. Each line had to be checksum-ed manually.
Here is Dompier's music program and song data in HEX format, ready for a 1702A ePROM:
I repeated this process for a total of 6 1702A ePROM chips. Each line was manually checksum-ed.
Pictured is the Processor Technologies PTCO 2KR0 1702A S-100 ePROM card. I used an ePROM "burner" to copy Steve Dompier's original music program and music data, plus tunes I converted from sheet music into HEX format. Each 1702A ePROM can hold up to a quarter of a Kilobyte (256 x 8 bits). The card is configured to store ROMs at 8000. Click image for larger view.
Pictured is a 16K Godbout EconoRAM IV S-100 RAM card. The RAM card is addressed 0000 - 3FFF but only the 0000 page is necessary. This card was selected because it was less "noisy" electrically than the earlier 8K EconoRAM II I had been using. Click image for larger view.
This is a photo of a California Computer Systems terminator card, used to help reduce S-100 bus "noise". Without it, the DAJEN has had trouble initiating the full ROM monitor. Click image for larger view.
Here are the connections on the back of the Altair and into the ADM 3a terminal. Note that there is a NULL Modem adapter on the Altair. Click image for larger view.
Photo of the Jukebox with the Altair 8800b cover removed. Click image for larger view.
The circa 1976 GE AM/FM Radio is perfect for the job. While the music program is running, AM-band radio signals are generated, producing music that can be received by a radio such as this. One can tune in the signal to reduce hiss and feedback. Click image for larger view.
This image shows the commands necessary to initiate the system. M is the "move" command and E is the "edit" command. G is for "Go". After the intial set up is complete each song can be loaded and played one time, returning to the DAJEN prompt ready for the next song. Ignore the ERROR messages, they are generated when one hits ENTER to escape the edit session. I am looking for a more elegant way to exit, but it's not really an error when you do. Click image for larger view.
> M 8000 80FF 0000
(move contents of 1702 prom containing music program to 0000)
> E 8
0008 00 D0 D0
(edit program to return to the monitor prompt, D0 after one play.)
> G 0000
*plays "fool on the hill" over AM Radio 1x and returns to SCI > prompt.
> M 8100 81B0 0020
(copy music data located in this block to RAM location 0020, over-writing what is currently there.)
> G 0
(run the program to play newly-copied tune.)
In all I created the following:
El Condor Pasa
In the Mood (among the first songs ever recorded played by a computer to generate signals received by AM radio )
Star Wars Theme
This Land is Your Land
You are My Sunshine
* * *
Pictured here is an RS232 breakout box used to turn off the RTS / CTS signals from the terminal. The DAJEN developed an issue that Corey Cohen identified as being a "stuck high" clear to send (CTS) signal. This problem caused the terminal to be unable to transmit back to the computer. Other than that exhibiting the Jukebox at the Vintage Computer Festival East 2018 went great. Click image for larger view.
|Hack A Day Writeup||by Bill Degnan - 08/03/2018 22:01|
SDR ON THE ALTAIR 8800
by Tom Nardi
Thanks Tom, glad you liked the exhibit.
|Altair Jukebox Video||by Bill Degnan - 08/27/2018 08:11|