Oct 132012

Looking at the traces from the last post I wonder if something as simple as a capacitor in parallel with R1 and R2 from SCLK and SDAT to ground wouldn’t be enough to filter the LCD update noise and allow the BlinkyPov to finally program.

Sensing Leds

The question is, how much capacitance, and will enough capacitance to filter the noise be too much for the LED / photo sensor to drive.

Grabbing a random cap out of my parts box turned up a 1uF electrolytic. I hooked it across R2 with some hook grabbers and grabbed some scope traces.

Here is the first trace without any added capacitance.

When I first ran the web programming app I had the bit delay at 40 msec. At that rate with a 1uF cap the loading was such that the data line was not moving much at all. Slowing the data rate down to 200 msec and then 500 msec resulted in this trace.

I think I’m onto something here. Assume that everyone who has a blinky pov can solder, seems reasonable since the blinky pov is a kit that requires you to solder it up in the first place. It is not unreasonable to think most people with a blinky pov could solder a small cap dead bug style across R1 and R2. Then with appropriate slowing of the blinky pov web page you might be able to get to a reliable programming solution.

It is late where I am so I’m not going to figure out the proper value of the caps tonight but if someone else comes up with a good set of values please leave them in the comments below.

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