Simple VGA Imaging System for SEM

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Hi All,


It's been a few months since I last powered up the Papilio Duo, but today I have it running with ZPUino and the Adafruit GFX graphics library.


The aim is to create a simple, stand alone  imaging system that can be used to capture images from a Scanning Electron Microscope (SEM)


The 800x600 VGA available will be fine for displaying static captured  images - but I think I might need to hack the VGA resistor chain, so that I can produce an 8 bit monochrome image, possibly with an 8 bit colour overlay.


The scanning system will be a pair of 12 bit DACs allowing an overall 4096x4096 field of view, but the VGA will only offer a small window into this  - say 512 x 512.


Image storage will be 8 bit monochrome bitmap to the SD-card on the retro-computing shield.


Attached is a 720x576 scan of some artificially generated, unsynced test pattern.   White field on LHS and below is for tool icons and text captions below


As usual I will keep you posted to progress.





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The HDMI Wing sounds interesting.   What video resolutions are anticipated with


1. Papilio Duo (2MB SRAM)

2. Papilio Pro (64Mb SDRAM)


I'm also looking for guidance from anyone who has used 100MSPs+  flash ADCs - such as in FPGA based oscilloscopes.








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  • 2 weeks later...



this sounds to me like a job for a DC-coupled 2-channel digitizer.

It's a fairly standard component, but not one that I'd want to re-invent all by myself.


When data is coming in at e.g. 100 MSPS x 16 bit x 2, you'll need to do design carefully (Spartan 6 is "low-power" category, not high performance. Think memory bandwidth).

You'll find ADC "eval" boards aka poor man's modules from Analog Devices or TI, but they can be full of surprises (such as, a USD 500 board comes with half the features missing after a redesign - been there, got the T-shirt. Not to mention uncertain availability).


Here would be a complete open-source hardware solution with two on-board 125MSPS x14 ADCs.


BTW, over the years I've done improvised digitizers with a soundcard, two ADCs eval boards and a logic analyzer, a sampling oscilloscope as a software radio frontend, or by putting probes into the IQ ports of vector radio signal analyzers.

Usually most of the work goes into what I do with the signals, not how I acquire them. So keep that in mind, it's maybe the smallest part of the job.


And FPGAs tend to make people underestimate the workload by a typical factor between 100 and infinity-minus-seven :)

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