S
Spehro Pefhany
- Jan 1, 1970
- 0
Well, it looks like it is time to call it a day. I spent two days
this weekend testing, and calibrating four units. On the bench, they
all worked great, and gave good results across my entire test samples.
This morning, I mounted them in their final cases, and hooked them up.
Two failed immediately, basically decided everything I tested was
white. Two appeared to function, but as soon as I started testing,
failed on every 'corner' case in my test samples. Took one of those
back to the bench, and the calibrations had shifted drastically. Funny
thing was, the shift was to needing more gain, not less, which the
'all white' indications would have indicated.
Technically, I have been 'measuring' gain as the setting on the
digital pot that gave an almost full indications on the ADC. This
gave me values from 0 to 255. When I measured this unit on Saturday,
it had gains of red 239, green 239 and blue 226. On Sunday, when I
finallized the program, it read 231, 233, 214. This morning, after
retesting, it calibrates at 245, 241, and 231. So, a shift of over 5%
in just two days. There might have been temperature or background
variations, but the background measuremnts have been stable at a
reading of around 8 - 10 on a scale of 2048. I am totally baffled!
So, after a year and about $2000 in materials, looks we are going to
forget this product, unless some of ya'll have any ideas.
Just for kicks, try hanging a couple of 10n caps from output to
inverting input on those MCP op-amps. (between pins 1/2 and 7/6).
It's possible they're oscillating, particularly the first one.