MC14490

I’m back

Took some time off. Been quite busy. That and I was having some issues and needed to step back.

Tonight I messed with the CPI values a bit and removed the multiplier. The multiplier works well on the desktop but in games it makes movement… strange. But the big win was replacing the 100 pF capacitor on the MC14490(debouncer) to a 1000 pF capacitor. This slowed the oscillator allowing for more time between register shifts in turn allowing for a longer debounce period. This change fixed all my bounce issues! I still want an oscilloscope to actually see the bounce and how the different debounce methods affect it. I am just guessing, which I don’t like doing.

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DSC_0251_smallSo I have been using this as my primary pointing device for about a week now. I have changed the button position and stylish clay palm rest close to 30 times. There still not exactly where I want them but its close enough where I can now start figuring out how I’m going to mount the buttons.

The motion of the call is working better than I ever expected it would. Its as smother than any trackball I have ever used. The Z-axis is still a bit wonky for some apps. Currently when you press the left bottom “button” it changes the CPI from 5040(max) down to zero(min) and uses the X-axis value as the Z-axis value

Originally I had set up a “PinDetect” object for each button to debounce them.  This worked fairly well but no matter what values I changed the frequency and sampling numbers to I could always get either clicks that did not register because i clicked to quickly or clicks that registers more than once because the bounce was to long. Even if i could get it working as i wanted to as a programmer I have never been a fan of polling. Its generally a waist of resources and in some cases lead to unexpected behavior especially when there are going to be 6 or so polling so tightly(~20ms).  I just don’t like breaking the program flow like that. I realize the MCU is complete overkill for a trackball and I have more than enough ticks to spare.

Because of my aversion to polling like that on my last Mouser purchase I added a MC14490PG from ON Semiconductor.  The chip is ludicrously expensive at $4.77, hell the LPC11U24  MCU was only $3.92. However it was easy to wire up and in my opinion a more elegant solution, and so far I have not seen any unwanted behavior.  There where few other debounce solutions I read up on and may test out, but for now the MC14490PG it is.

Though I would still like to get my hands on an oscilloscope. It kills me not being able know what is actually going on when one of the buttons is pressed. If I knew how long, on average these switches bounced for I might have been able to fine tune the “PinDetect” objects better

On another note I came across Dialight, which among other things makes SMD LED‘s and light pipes, lots of them! (What can I say odd things excite me 😀 ), Mouser/Digikey even have them in small quantities. Not even sure if I am going to do anything more than standard 5mm/2.5mm round LED’s but its nice to know the option is there.

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