This week, June 17th, Derek Robinson will be hosting an evening of discussion about "brains" - artificial intelligence, neural networks, signal processing, etc., at InterAccess.
After the "sensors" discussion last week, and "brains (transform)", I suggest next week we should look more in-depth at "express": actuators and power systems, eg. motors, solenoids, etc., and how to control them to animate artworks. After that, we'll be looking for more topics and volunteers, so please post any ideas, offers, or requests.
The InterAccess Programming Committee has approved some funding for our activities this summer, so we should plan our first intensive workshop/seminar, perhaps for two weeks from now if possible. From talking to various people, I get the impression that a general "electronics" workshop, covering basic theory and the use of tools (multimeter, oscilloscope), and fabrication techniques, would be most popular. It might also include the "Active Surplus Walking Tour", and/or an in-depth look at other parts sources. Any other ideas? There's also some money available to pay someone for some general research and development of the web site, as well as several hundred dollars for materials and equipment. So we'll need some discussion of how to go about this... please post any proposals you may have.
Some people have been saying that it might be a good idea to plan a preliminary exhibition at InterAccess in September, to "workshop" half a dozen pieces or so, and to start experimenting with ideas for networks and interaction. This would be a great way to get started with production, and we could then plan to have a larger show in January or February. What do you think?
As you may know, the Web Grrls group will now be meeting at InterAccess on the third Tuesday of each month, starting July 15th. They couldn't meet any other day, so we decided we could accommodate that by having a "shop day" at Graham Smith's studio, or other field trip, on those days.
Previous meetings: Yod Lafarge presented his bird/gargoyle sculpture which is powered with pneumatic cylinders. It contains a small video monitor with images taken from television during the Gulf War. The wings, made from metal strapping and bolts, flap when motion is detected by an infrared sensor. Yod used a small aluminum air tank, which was pressurized by a tire-inflation pump from Canadian Tire. He used a pressure sensor, manufactured by "Johnson Controls", to turn the pump on and off at the appropriate pressures. The sensor, and a number of the other parts, were surplus material from the University of Toronto's labs. The "Bimba" brand cylinders were from Active Surplus - Yod mentioned to be sure that the cylinder has a place to attach an air hose, since most of them are missing and just have holes. Jean Trivett pointed out that most of the hoses and connectors could be found at an aquarium supply store.
There is a circuit diagram at : http://www.interaccess.org/arg/pix/yodiagram.gif
The infrared motion detector enabled the animating circuit, which consists of a 555 timer chip which triggers a 3055 power transistor to drive an air-flow solenoid. When the solenoid is activated, air flows from the tank into the bottom of the cylinder, pushing the piston out. Air from the top of the cylinder escapes through a constricting valve which can be adjusted to control the speed of movement. When the solenoid is deactivated, the air flow path is switched around; air flows into the top, pushing the piston back in, and the air from the bottom escapes through the valve. There are switches at the top and bottom of the piston's travel which set and reset the 555 timer, which controls the amount of time that the solenoid is activated for.
Colin Hinz then showed his robot, which he built using a home-brew Basic Stamp several years ago. The robot uses four switches to detect collisions with objects and to change directions. The motors are driven using an L293 peripheral controller. Colin explained the circuit and program, which he has promised to summarize in the discussion forum (sorry, I was sick that day and my notes kind of stopped at this point...
We also saw videotape of the Electric Skin project, which used two small telepresence robots to explore thirteen artists' works created for the show. Jeff Mann pointed out that this was a very successful show, in part because of the kind of parameters the artists had to work with, and that we should keep it in mind for our own exhibition plans.
Bruce Hearns showed us a "Kilodney Plate" - a piece of sheet metal with sand on it which showed the resonance patterns when the plate was played with a violin bow. The rest of the meeting featured a demonstration of shop tools and techniques. Graham demonstrated how to drill and tap threaded holes in aluminum, and how to use his bandsaw, drill press, and other tools. He mentioned several places to buy metal and scrap: Solway's at Lansdowne and Bloor, Rotblott at Bathurst and Front, and Atlas (for tools) on Queen near Duncan.
Victoria Scott then demonstrated the use of a die to make threaded steel rods, and mentioned that Jacob's Hardware on Queen near Spadina was a good source of tools and supplies. She also showed various types of fasteners, including pop-rivets (use the same kind as the metal you are fastening to avoid corrosion), etc., and demonstrated the use of a propane torch to heat and bend pieces of welding rod in order to easily create armatures and other structures.
Last week, June 10th, the topic was sensors. We concentrated on the use of the "POT" command in the Basic Stamp to measure sensors that work by changing their electrical resistance. Jim Ruxton hooked up a photocell, a.k.a. light-sensitive resistor, to the Stamp. He showed us how to use the Stamp programming software to calibrate the stamp to the size of the resistor. The useful range is about 500 ohms to 500k ohms. Jim created a circuit that would switch on a fan or position a hobby servo motor when the light reached a certain level.
Jeff Mann noted that a pot (potentiometer or volume control) can also be used, and showed how to find the overall resistance of a pot (measure between the two outer pins), and how to wire one for use with the Stamp - use the left and middle ("wiper") pin. Bob Bernecky pointed out that connecting the right pin directly to the centre pin can help reduce electrical noise. It was also noted that we should use linear pots rather than log (audio) pots with the Stamp, and that this can be tested by putting the wiper in mid-position and testing to see if the resistance between it and the left pin is equal to the resistance between it and the right pin (linear) or quite different (log). Jeff also showed a joystick made of two pots, and how this could be used as a level sensor or accelerometer.
Paul Davies showed his gamma ray detector, which was used in an art installation. The insides had been replaced with a circuit that Paul built to sense magnetic fields, using a Hall Effect sensor, model #5549. Allegro Semiconductors sells these; watch out for others which may only be switches rather than variable sensors. There is also a digital compass chip available.
It was noted that Hall Effect sensors, like many others, use a changing voltage output rather than changing resistance, which means there is no direct way to use it with the Stamp. Several approaches were discussed, including the use of a serial Analogue-to-Digital converter chip (see the Basic Stamp application notes), amplifying the sensor to drive a light bulb and then sensing that with a light-sensitive resistor (photocell), or using a voltage-to-frequency converter and measuring the frequency using the Stamp's PULSEIN command. Jeff mentioned that there is a "Basic Stamp clone" available, called the Pic Stic, which has two channels of A/D conversion for about the same price as the Basic Stamp.
We made a list of resistive sensors that could be used directly with the POT command:
Afterwards, we retired to Squirelly's where we spent vast amounts of money as usual. Don't think I can afford this anymore - how about staying at IA? There's food nearby, and we can bring some music... just a suggestion...
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- potentiometers, including "faders" and home-brew devices using resistive wire, graphite (pencil lead), electrodes in liquid, etc.
- photocells, can also be used with lenses and hoods for more directionality
- thermistors to measure temperature
- strain guages which measure force, may be expensive but are very linear
- black conductive foam sandwiched between metal plates to measure pressure
- some humidity sensors
- force sensing resistors (see http://www.interlinkelec.com/ )
- carbon microphone from an old telephone*
- human skin *
* these may be out of the useful range of the Stamp!
Jeff Mann