The goal of this project is to see what can be accomplished with little hardware. The goal is not to compete with existing products or even bring it to market

Probably I expressed the idea not clear enough but You seems cordially misunderstood what I am saying.
I said 1) the probe itself is minor value thing whilst the optoinsulated probe is gold worth value
I said 2) nowhere to buy such opto-probe except for money what is too big even for large scale millioneer firms
I said 3) exists few good DIY circuitries solving that problem, but their BW is too small for practical measuring habits
I said 4) there exists a certain tradenames using within existing circuitries the demanded BW may be attained or at least near of it.
I said 5) its worth to make a ``new optoinsulated probe`` common-joint engineering Project

And may add now - that to construct a new kind of DSO according my understanding of things looks like a waste of money and energy, when one day salary is enough to buy a readymade wonderful instrument instead, what to make by own hands would demand at least the month work and cost the same money.

 

I said 1) the probe itself is minor value thing whilst the optoinsulated probe is gold worth value

I worked on a prototype for a 100MHz fiber optic scope probe (analog) back in the late 1970's when I was an R&D tech. We chose to use the shell and battery from an HP970A DVM. The intent was to develop a probe that addressed current loops caused by the ground lead. I worked on the 100MHz front-end, another team member worked on the back-end, and another was working on a system for making the optical fibers. It never became a product.

 

Here is the first screen shot of the prototype. All aspects are subject to change.
The grid lines are in light gray and do not show well on the screen shot. They are fine on the actual device.
The sine wave is computer generated.

I still have to work on the screen controls.
I think I will have a go at the bluetooth interface next.

 

Bluetooth connected. This is live data captured from a not-so-linear sine wave generator.

Many things to work on now:

1. ADC DMA interface
2. Triggering
3. Screen controls
4. VOLTS/DIV
5. TIME/DIV

 

Nice progress!

 

ADC and DMA implemented.
Sampling frequency = 50Msps
Test signal is 8.000MHz
With 125ns signal period and 20ns sampling period there are only 6 data points per cycle.

X-axis and TIME/DIV are now both calibrated and functional.
For the time being, trigger point is at left side of the screen.

 

ooh! Some nice competition here. It never crossed my mind to use the touch screen to control the waveform display. This at least eliminates the X-position and Y-position adjustments which I had originally planned to implement with sliders. Then I am going to use pressing on the center to reset both X and Y positions.

I've got me some more coding to do!

 

I am gradually working my way through the GUI touch screen interface.

What I have now are:

1) Touch and drag the green 0V line to set the DC offset.
2) Click on screen center to set 0V to center line.
3) Tough and drag the red arrow on left side to set DC trigger level.
4) Tough and drag the red arrow at top to set trigger t=0 position.

I still have time and voltage cursors to come next.