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A project log for sdramThing4.5 "Logic Analyzer"

An AVR, 128MB SDRAM DIMM, old laptop LCD, and a handful of TTL chips -- 30+MS/s 32-channel logic-analyzer interface for an analog 'scope

eric-hertzEric Hertz 01/31/2015 at 09:360 Comments

Spent a large chunk of the day getting rid of the test-clips all over the place... Spent a large chunk of yesterday figuring out where they had to go in the first-place.

So, now there's a screw-terminal block for the 'scope outputs and data inputs, and a header(!) for the "remote" (button interface for the cursors, based on anaButtons).

Currently it only handles the two channels ("Red" and "Green"), but the terminal-block is big enough for 6, and the portion of SDRAM dedicated to Sample/Repeat is 32bits wide (DIMMs are 64bits, the first 'bank' is dedicated to the "free-runner" and the second bank is for the "side-kick" which handles SAR). Obviously, only two channels can be *viewed* at a time (the two colors on the LCD, and two traces on my 'scope), but all 32 are sampled/repeated simultaneously... And there're thoughts along the lines of means to slow-down repeating for e.g. uploading to a computer... There're thoughts about *everything* ;)

Also, spent a bit of yesterday revisiting the code... updating it to use newer versions of commonThings, a little bit of debugging, etc. But mostly just reminding myself how it works, which pins to use, etc. since I never did write a user-manual.

But, now that it's wired-up in a reliable and intuitive way, I've run into a couple other slow-downs...

First, the data-source is 5V-logic, whereas the SDRAM is 3.3V... So, time for a 74AHC-series buffer... my stock is rather low, but not nil... plausibly I'll be using some XORs for the purpose. It's a good idea for the future, anyhow, 'cause the other slow-down may render the current mishmash goals difficult.

The other slow-down is that the printer was dead last I tried to power it up... It blinked for a second, I heard the stepper tick, then it powered-down. Aaannnddd... I got a bit overzealous(?) in tearing it apart for the X-axis experiments (with the encoder), making it even less-likely to get as far as ticking that stepper-motor. Yeah, I all but destroyed the possibility of wiring it all back together; The ribbon-cable's been soldered and epoxied, the inkjets themselves have been stripped from the carriage (and basically *ripped* off the ribbon-cable, 'cause it was darn-near impossible to access), the opto-sensor that detects the edge of the paper has been removed (and was on the unusable ribbon-cable anyhow)...

So, as it stands, I get nada. Switching on the power-supply causes the power to go active for a second, but no data's sent to the driver-chip... none of the very data that I was planning to spy-on with my logic analyzer.

All hope is not lost, but steam may be winding down.

Oh, and my hands are still covered in ink from yesterday's cleaning ;)

Oh, and... I wrote a nice project-details yesterday, summarizing the idea behind free-running SDRAM... and then outta-the-blue literally seconds before submission, my kernel halted.

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