I just purchased three Maxbotix ultrasonic proximity sensors from Spark Fun Electronics.
My first impression is that they are really, really small. I expected them to be small, but my, they are very small!
I hooked it up to +5V, and was pleasantly surprised by a lack of audible sound. The previous Polaroid sensor based ultrasonic sensors I've used all gace off a "tick...tick...tick" sound. The sound was useful in my project Blame, but for Sycophant II, I wanted something quiet.
I monitored the analog voltage output, and the Maxbotix sensor gave very good distance results for human body trunk detection out to about 100 inches. As the datasheet suggests, the beam is very wide for thick objects out that far, about three to four feet wide around 8 feet out. This is unlike some of the Sharp IR sensors, which have a very narrow beam.
In Sycophant, I had to very carefully angle the IR sensors so they would effectively track the viewer. I was also running them at the far end of their sensitivity distance. I feel that I could very easilly run the Maxbotix sensors with a sensing range of about 6 feet, and have excellent side-to-side coverage as well.
I've gone back and forth on which microcontroller I want for Sycophant II. I've been looking at BASIC-enabled microcontrollers with analog in (for the ultrasonic sensors) and easy serial out such as the PICAxe or the Kronos Robotics Perseus, but both of these are a bit exotic, and I figure if I get sick of doing PIC assembler, I can go ahead and purchase the microEngineering Labs BASIC compiler. Or heck, I've got the PIC C compiler working, so I could use that as well.
So I picked up a couple of PIC 16F688's which have up to 8 channels of 10-bit A/D and a USART.