Input Devices

Input Devices


Dan Schulz for helping with Eagle and some design quesitons. Candle Power Forums for providing help with perceived brightness vs actual brightness. Matt Blackshaw for debugging the changes in FabModules.

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Candle Power Forums

“A program is a spell cast over a computer, turning input into error messages”

- Anonymous
This week I wanted to do part of my final project so I won’t have to scramble as much towards the end. Part of my project that involves an input sensor is the ambient light sensor. When the room is dark, not as much light is needed to see the clock. In order to prevent the clock from keeping someone awake, the 7-segment display will dimmed to conserve power and to reduce the strain on your eyes.

The first board I created suffered a case of leprosy. Copper traces started peeling off the bone and I’m pretty sure it’s because I took too long while soldering. I may have melted the fiberglass beneath it. The second board I made to replace the first suffered from the traces being too small to mill correctly. After Dan helped me figure out the error checker in Eagle, I was off to the races while milling my third and final board. I soldered the parts and everything worked as expected. The board programmed without error and I got FTDI up and running right out of the box.

That left me with a lot of time to program the output and to realize that LED Brightness != Perceived LED Brightness.

LED Brightness != Perceived LED Brightness

I spent some time on the net looking up why my LEDs seemed to be brighter than they should be given a specific voltage and I learned about image persistence in the human eye. That’s why videos can play 24 frames a second and we perceive it as smooth motion.

In my research I also learned that current dimming is apparently much more efficient than PWM dimming. My Clock should get considerably more run time on down to 0.5% current dimming, but PWM dimming results in less color shift. A combination of the two approaches could solve both problems, but it will take some time to figure out how to work it.

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