A while back I was thinking about delay lines in old vintage electronic devices. There are
many kinds.
For some unknown reason I wanted to make an
optical delay line. These already exist of course and they are used to do things like fractional phase shifts of high frequency signals and often give delays in the region of nanoseconds thereabouts.
That's no good to me, I want a delay of a few seconds! But rather than buy several hundred thousand kilometres of fibre-optic cable, I decided to do it a different way...
Imagine a plywood disc about 100mm in diameter. Around the edge we have 40 holes drilled, each one containing a glow-in-the-dark ("
GITD") plastic ball ("
BB"). This disc can rotate and is driven by a stepper-motor by way of gear teeth around the disc's perimeter.
Attached is a
very basic sketch of what it might look like. I haven't shown the motor or any of the electronics.
Theory of OperationEach of the 40 BBs represents one binary bit, giving us a generously capacious 5 bytes of RAM. If a BB is dark then it represents a
0 bit, if it is brightly lit or "charged", then it represents a
1 bit.
The disc will be in constant motion and each BB will need to be periodically "refreshed" by passing through a "read/write head".
Each read/write head will consist of a light sensor and a powerful light source of an appropriate type. If a 0 bit needs to be refreshed, then no light is applied to the BB because natural decay of the phosphor will reinforce the zero value. If a 1 bit needs to be refreshed, the powerful light is applied to reinforce the 1 state.
So the RAM is implemented as a 40-bit analog ring buffer ("
Ring" henceforth).
To begin with, the ring will contain only 0 bits (all dark). A microcontroller will control the stepper-motor and thus the disc's motion. The same micro will control the read/write head(s). The micro will provide a simple RS-232 interface through which a human user may interact with and control the machine.
The user will be able to write a brief message (up to 5 whole characters!) that will be written to the Ring and held there perpetually or until the machine is switched off.
When the Ring contains a message, that message will be endlessly read and echoed back to the RS-232 terminal from which the user may derive tremendous joy and enrichment.
ExpectationsI don't know if this will work. I think it
might work if all the many variables are under control, but I'm not certain.
Ultimately I'm hoping to make a simple and mildly amusing interactive gizmo that demonstrates an idea that we can use obscure physics phenomena to store even small amounts of information for later retrieval.