Tues Jan 27 RDNO

Well its been another long time since I've updated. I haven't done a thing with that PS2 controller. Much of my effort has been centered around getting the Milwaukee Robotics Club up and running. The first club contest will be Mini-Sumo.

To that end I've been working on getting a detection scheme working that I saw many years ago in Atlanta on the robot Delta Force. Tonight I got the two high-power LEDs running 1.32Amps for 10us, 300 times per a second. And they didn't burn up! It was tough to get higher than that. I ran them with a variety of current limiting resistors and found that the lower the resistance the less voltage the resistor would drop. I think it is likely that I'm not turning my FET on all the way. They are supposed to be TTL compatible, but maybe just barely. Or possibly the voltage drop of the LED starts to get wonky at these high current levels. Still 1.32 Amps is good enough. The sheet says they are rated for 2 Amps for 10us, 300pps.

The detection circuit was much tougher. I don't fully understand the circuit he is using. I am pretty sure that the first stage is a current to voltage converter and the second stage is a regular voltage non-inverting amplifier. However, there are clearly AC aspects to the circuit and those are a bit beyond me. I think the circuit is designed to pick up the momentary current flow that results when the photodiode changes capacitance due to incident light. On my bread-board I was able to get it pretty much working but with only a half to one volt change with a 1 volt bias. I messed about with the circuit quite a bit to try to get a higher voltage swing out, but all I did was demonstrate my ignorance of the fundamentals behind the circuit. Worse, later I *think* discovered a serious wiring error even though the circuit seemed to have been working. After correcting it the circuit seem to have a strange warbling noise that was not present before. However, the circuit seemed to still function, just with the noise added in. It was starting to get late so I left off.

I think my next step is to either make an etched pcb for the detection circuit or do point-to-point on one of Eddy's nice prototype boards. Bread-boards are super great for messing about with the structure of a circuit. But, they are sloppy. Things pull out of the sockets under the weight of o-scope probes, leads get pushed down and into other leads they are not supposed to touch and there is stray capacitance aplenty. And anyway, as was made apparent to me tonight, I am not qualified to mess about with the structure of this circuit. With a soldered-up etched or point to point circuit I am hopeful that I'll get better results.