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Old 08-26-2007, 10:15 AM
Grant Stockly Grant Stockly is offline
Join Date: Jan 2005
Posts: 447
Default Kenbak-1 Music Project Idea

This isn't my first project idea for the Kenbak, but it is the most practical.

The goal is to make the Kenbak play music.

The 8 data lights on the Kenbak-1 do not display data being transfered within the computer like on the Altair and other common "blinkin lights" computers. Those 8 lights are a memory mapped location in memory.

My preliminary plan is to connect an R2R ladder DAC to output lights. The R2R ladder can be scaled for 8 bits.

The lights have a glitch lasting about 10us every 1.2ms because of the data being shifted into them. A latch connected to a status bit inside the Kenbak may be necessary to hide the glitch from the R2R but for a prototype I don't think its too necessary...

The DAC would create a voltage from about 0v to 2.5-3v for the average values. This voltage would be used by a voltage to frequency converter to generate an audible tone.

I would like to make the circuit with parts available in 1971, just for fun.

Any suggestions for the headphone/line audio amp and voltage to frequency converter? I'm thinking a 555 timer with an input and output transistor would work great.
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Old 08-29-2007, 12:22 AM
Cappellanus Cappellanus is offline
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Join Date: Jul 2007
Posts: 24
Default Kenbak DAC...


Like the idea of the Digital to Analog Converter. The main problems with the Kenbak is lack of input and output. The DAC going to a Volt-Freq. Converter would allow a pretty interesting project.

I'm glad you checked output light signals. I had figured they would not be a steady logic 0 or logic 1, but didn't know how significant the glitch would be. Your quantification of the glitch isn't bad. A low-pass filter (capacitor) would easilly smooth this, as I suspect notes would only change every 100 milliseconds or less.

The 555 timer idea is interesting. The history of the 555 timer is right here

The inventor says Signetics first produced them in 1972, so it's about the right vintage. Interesting, they say the 555 timer is the most produced IC of all times, an order of magnitude above the competition.

We could read from a table of notes and durations to play a song, but what fun is that? It would be cool if an algorithm could produce an interesting recurring sound? Has anyone ever seen a "music" algorithm that gives a fairly interesting complex "song-like" tune? Preferably without too many instructions? If you search for "music algorithms" on google, you get a ton of links. But something simple that can be machine coded into a handful of bytes? I don't know. I suspect we really need music algorithms from the 1970's, before hobbiests had good access to modern machines with unlimited memory and high level languages.

- Steven.

Last edited by Grant Stockly; 09-10-2012 at 09:19 PM.
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Old 08-29-2007, 04:28 AM
Grant Stockly Grant Stockly is offline
Join Date: Jan 2005
Posts: 447

I think that we also need a 13 input NAND chip (forget the number) to cut the timer out when data = 000. We need rest notes!

I was thinking that since memory is limited we have a lookup table for notes. Limit the number of notes to 32 or 64.

Use the 8 bits of memory to store note and duration. For example tttnnnnn. 32 notes and 7 note durations.

note xxx00000 would be a rest.

Because the 32 notes would be generated from a lookup table they can be any note we want. We don't have to define notes not part of the song.

32 bytes of ram for notes seems like a waste. Maybe we only need 16 notes. Then we could fit two notes in each byte...

Its interesting...
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