Physical Digital Lookup Table

I am always intrigued by the idea of executing simple computational tasks to do with digital sound and audio using logic chips only - for example, you may recall the work I have done with audio sample manipulation using EPROMs and RAM chips.

Yesterday I prototyped a very simple version of a proof of concept for a physical digital lookup table. The idea is that I wanted to be able to actually see and physically interact with digital memory with my own hands. I will be expanding on this idea.

A set of thirty-two bits, organised into eight nibbles of four bits each were created using physical connections to a voltage supply. This series of physical connections were then multiplexed on a bit-by-bit basis, after which the data is sent to a simple four-bit digital to analog converter. Thus, each four nibble value can be read by multiplexing the data to the digital to analog converter.

Read operations are accomplished by setting each multiplexer to the same input / output gate. Write operations are accomplished by physical re-arranging the connections.

In the pictures below, the lookup table holds the values for a digitised sine wave whose values had been pre-calculated.

The completed lookup table.

Data stored as physical connections.
The yellow jumpers are 1s. The green jumpers are 0s.

Actual recorded waveform.