Cliff Hacks Things.

Tuesday, May 13, 2008

I can see clearly now, the waves are gone

I'm a pretty hardcore guy when it comes to debugging software. I pride myself on my automated tests, I routinely sling debuggers and disassemblers around, and so forth.

When it comes to hardware, though, I've been stuck firmly in the printf era. The printf era is pretty damn powerful, of course, when you've got Forth at your side -- the PropellerForth VGA and NTSC display drivers, for example, were written using only a multimeter and ancient HeathKit frequency counter.

However, I'm not a big fan of making my own life difficult. After many years of fondling scopes at Fry's, I finally gave in and picked up a Tektronix TDS1012B. It's at the high-end of the extreme low-end: decent sampling rates for embedded work and so forth.

A couple weekends ago I taught myself printed circuit board and built the PFcam, the Propeller-based image processing board I mentioned in my last post. I'm not an analog electronics whiz, so the first thing I did with my scope was test the new board.

Sure enough -- here's a capture of some I2C traffic between the Propeller and the camera:


Notice the square waves are wearing hats? The regulator's output was bouncing between 3.3v (the goal) and 5v (the input). A decoupling cap later, my SCCB code (Omnivision-speak for I2C) is much more reliable:


Now all the I2C/SCCB chips play nice together, and nobody wigs out and sees a stop condition where there ain't one.

I'm happy with the scope so far. I'll most more details on the PFcam board later on.

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