It's been awhile since, I did those experiments. I'm getting close the to actually build the project now. posting on the forum was the last try at it with arduino before learning to program and buying hardware for the pic. the circuit was exactly the same as fig 1 but, I had a resister in place for Rx (i didn't have a tds probe to play with). i tried many different values of resistors. Can't find the sketch i wrote back then. I think i may have deleted it after reading somewhere that the pins on the arduino where wrong kind. As far as the code i wrote, it basically went step by step with whats on page 3, in that paper i linked, changing pinModes to match the step and testing on the right pin using a while loop and a counter to see how long that pin was HIGH (i try many different delayMicroseconds in the while loop very small to larger to no delay at all). It also showed a picture on page 4 of what the oscilloscope should look like. testing the circuit with my oscilloscope it looked like very straight up and down spikes on the scope, like when pins switched to an INPUT, the pin grounded and the voltage in the cap dropped very fast without going thru the resister. This seemed to support what i read about the pins being wrong so, i gave up at the time. I'll have to rebuild the experiment again. I'll be able to do a much better job of now, having a lot more practice writing code for the arduino.
thanks, red