Re: [sdiy] Grounding + scope update

[Roman]

this is my idea for some time now. No schematic still, but couple of thoughts:
I was thinking of using fast ADC with 2 sets of buffer RAM. ADC is constantly running and writing first RAM. When it's filled, switch to second RAM, and the micro processes first RAM. 4-8kB may be OK. LCD has only 240x320 (the one I want to use), so why bother with 8k of samples? That alows for peek-detection, so I could see about 150ns spike when viewing one cycle of 1kHz. To make it fast enough it may be easiest to use DSP for sample processing. It would find lowest and highest sample in 8k/320=26 samples. The it would write directly to LCD controller RAM.
Triggering is anouther issue I have not resolved yet. It may be analog or digital. Analog trigger would flip the RAM buffers when trigger condition occurs. Well, maybe not at once, but half of the sweep cycle later, so we'd have triggering signal in the middle of the screen. Adding appropriate delays we'd get pre-trigger and post-trigger displays. If triggering was to be digital, the DSP should also check for trigger condition and here we have more options. Not only a threshold, but also pulse width, slope speed, etc. It all should be fairly easy to detect.
With a little effort DSP could then measure RMS, peak-to-peak, frequency, period, FFT (yeah, right) etc. but that's an overkill IMHO.

I was thinking about something like 40MSps dual channel.
So far I have only made LCD driver, although it's very old design, made for an old, dead project.

Roman

---- Wiadomość Oryginalna ----
Od: Pete Niedermayr <pniedermayr at qwest.net>
Do: Thomas Dunker <dunker at invalid.ed.ntnu.no>, synth-diy at dropmix.xs4all.nl
Data: Thu, 29 Apr 2004 19:47:11 -0500
Temat: Re: [sdiy] Grounding + scope update

>I have a couple of 7.2" LCD monitors (Legacy LM7) and was thinking this
>would make a good display for an oscilloscope. Any thoughts or schematics?