Monday, August 21, 2006

Maxbotix Ultrasonic Sensors First Look

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.

Friday, August 18, 2006

Dorkbot DC August meeting results

You can read all about the August meeting of Dorkbot DC here, as well as coverage in the Street Tech Blog here.

I gave a presentation at the meeting: Sensors You Should Know About.




Friday, August 04, 2006

Dorkbot DC Meeting, August 15

Interested in technological art, robots, or just creating advanced technology?

Dorkbot is an international organization to explore all uses of technology in the development and discussion of art and creative exercise. This can involve practices ranging from virtual and interactive art to video and audio landscapes. The Dorkbot DC chapter has recently formed, and is growing quickly!

Next Meeting:
Tuesday, August 15, 2006
400 8th Street NW
Washington, DC 20004

More info at the Dorkbot DC web site.

Tuesday, August 01, 2006

Long Distance Internet Touch

Here is video of differential pressure touch between two fingers. The two RVHEs send packets with pressure info to a server 60 miles away, then the server calculates the finger positions and sends that back. A "helper" PC is in the middle to serve as a gateway between the RVHE LAN and the outside Internet.

Obviously some scaling and timing issues need to be worked out, plus I am going to move the pressure sensors from the fingertips to near where the fingers connect to the servos, but at least there is some hope of things working!

I was able to build a serial cable to connect to the SBC65EC, which makes it much easier to configure. I have greater hopes for this board now.

Looking for a free Windows DHCP server? Try this one from Uwe A. Ruttkamp. Don't ask me why the world isn't full of public domain and open source DHCP servers for Windows. It just isn't.

Moving forward with Touch

I got tired of trying to find a solution where the Ethernet-enabled microcontroller boards would exist on their own (due to not putting the router MAC address on UDP packets, or basically being unable to DHCP a router address, depending on board).

So I decided to just bite the bullet and use static IP addresses and a "helper PC" that forwards packets to the Internet server that connects the two ends of Touch together.

So I hooked up an RVHE (the big board on the bottom) to the Pololu Micro Serial Servo Controller (which is the very small board on the left). I'm using the same RS-232 connection that you use to program the RVHE in BASIC to connect to the servo controller, as is now defunct and I can't figure out where the second RS-232 port is on the RVHE from the documentation!


So now one finger of pressure sensor info is sent by a second RVHE through the "helper PC" program to the Internet server. The first RVHE also sends its one finger of pressure sensor info through the "helper PC" to the Internet server as well. The Internet server then sends back a finger position to both RVHE's through the "helper PC", and the RVHE's command the servo controller over the RS-232 connection.

This gives me one finger's worth of Touch to test out timing and scaling issues. I think the RVHE is a dead product now, so I imagine it won't make it into the final project. It is too bad, the RVHE was like a BASIC stamp with Ethernet, which would rule.

In other news, I think I might have found a solution to my Modtronix SBC65EC UDP ARP/DHCP problems. We'll see tonight...