Kenbak-1 Music Project Idea

[Grant Stockly]

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.