Service Dog Training Modules
About five years ago, my wife asked if I could conjure up an electronic training device for the Assistance Dog Institute (now Bergin University of Canine Studies). Bergin Univ. (BUCS) specializes in training dogs to assist people with physical disabilities and challenges. For more information about BUCS and its mission:http://www.berginu.edu/
Among the many things that service dogs learn is how to turn light switches "ON" and "OFF" for the physically-challenged people that they assist.
BUCS had developed a "training board" with a light switch and a battery-powered 12 Volt lamp. Unfortunately, the dogs don't pay much attention to the lamp, especially in a bright room. What was wanted was something to make an audible "beep" or buzz when the dog correctly flipped the switch with its nose. BUCS staff made a trip to Radio Shack for some help, but met with only quizzical looks and no ideas.
After discussing the application with Dr. Bonnie
Bergin, founder and CEO of the university, I developed
a tentative specification:
1. The training board should make a sound instantaneously as the dog flips the switch. This, along with a verbal recognition from the trainer, tells the dog "mission accomplished."
2. The sound must not continue, as it may take a while to reset the switch.
3. Ideally, the system needs to be portable.
4. To be safe, it should be battery-powered.
5. Battery life should be as long as possible, even if the switch circuit is not reset to OFF
This seemed to be an obvious application for the venerable 555 Timer IC. The 555 will generate an audio tone (square wave), operates from batteries, and a second 555 can be connected as a one-shot (Schmitt Trigger) to time out the tone. Since we still didn't know some things about optimization, I decided to build the first design with several adjustable items: pulse duration, tone frequency, and audio volume.
The first 555 establishes a pulse length adjustable from about 1 second to 10 seconds. The second 555 creates an audio tone that can be varied from about 400 to 1000 HZ. The board is hand-wired using a Radio Shack general purpose proto-typing board (no etching). This was a good first attempt and we learned:
500 to 700 HZ. is a useful and pleasant tone.
2 to 4 seconds is sufficient for reinforcement of the desired action by the dog.
CMOS versions of the 555 (7555) promoted lower current drain and standby current, in the event the switch was left ON.
Hand-wiring a "proto" board was slow, but effective.
After several months of use, more of these audio modules were needed. I decided to concentrate on a simpler design with a fixed duration and tone. The black plastic boxes were surplus items from HSC Electronics that were large enough for the need; the most difficult task was cutting a 2-inch hole for the speaker. A surplus computer fan grill was used to protect the cone. One of the "ace" BUCS volunteers, Marilyn Calderon, designed and built a trainer stand that could be adjusted for different sizes of dogs. The dogs begin training as young pups and continue until they are placed with a client when they are about two years old.
With the demand for more training stands, I decided that something cheaper, and more importantly, quicker to build, was my next chore. I experimented with buzzers and piezo transducers. These had acceptable tone, but stayed on continuously. It was then that my good friend, Phil Dunning, a technical consultant, came up with the idea of using a 3-way wall switch to charge a large capacitor. The switch merely transfers the charge from the capacitor to the sounding device. When the capacitor is discharged, the tone stops. The earliest version uses a single MOSFET as a switch, but by using a very large capacitor, the MOSFET is not needed.
This approach is low-cost and easy to build, but has an annoying drawback: as the capacitor discharges the tone and the volume of the sounding device change. So, back to the drawing board.
At this stage, we have new knowledge. A 3-way wall switch preserves the look of a standard light switch, but gives some flexibility in circuit design. The use of a large reservoir capacitor means that the sounding device is never connected directly to the battery. This reduces that chance for quick drainage of the battery. By using CMOS ICs and low-leakage capacitors, stand-by battery current is about 5 microamperes. Since an alkaline 9V battery has a capacity of about 450 milliamp-hours, the battery should last more than a year.
The new goal was to use only one 7555 timer to generate the tone, and somehow use a capacitor to fix the maximum duration of the sound. First I tried the simple 3-way switch with an astable 7555 tone generator. Worked well, but again, the tone and volume trail off near the end of the pulse.
It was at this time that I decided that I should have a dedicated printed circuit board established, rather than using proto-board and short wires for interconnection. More help from Mr. Dunning, who introduced me to pc board lay-out software. I quickly learned to draw simple boards, but still had the problem of producing them by acid-etching. In small quantities, etched boards are pretty expensive ($20) and require a minimum order.
I decided to etch my own boards at home, much to the chagrin of my wife. Since she is the Volunteer Coordinator for BUCS, she reluctantly ignored my etching trays, knowing it was for a good cause. Via the Internet, I learned about using a laser printer to generate photo masks for etching boards. Again, I was blessed with expert consultant help. Dr. Tom Mayer of Thetatek, advised me about transfer films and etching solutions. Eventually, we developed a workable process using swimming pool pH chemicals (hydrochloric acid) and extra-strength peroxide used for hair bleaching. It wasn't long until I could make workable, if not exactly pretty, copper wiring boards.
Phil Dunning came up with another interesting idea. Why not use the RESET pin on the 7555 as a simple time-out circuit? Using an R-C network, I was able to establish a 3 second "burst" of 500 HZ tone. Now I can do the whole trainer module with one IC and no direct battery connection! It was at this time that I learned about Carlon blue wiring boxes... available for $2 at Home Depot. The whole circuit, with the battery and speaker (salvaged from dead audio greeting cards), could be contained in one box and the cover could be drilled to make a speaker grille.
Extensions: Complex Trainers
After building about 10 of the various versions of the Light Switch Trainer, Dr. Bergin had needs for different types of configurations. A small board was set up for training puppies (beginning at about 5 weeks old). This is hand-held and can be positioned by the trainer.
A simple trainer was built for power-operated doors. These use a push plate instead of a toggle switch.
By far, the most complex trainer was the Elevator Call Button Panel. This required two separate circuits for UP and DOWN, driving one 7555 Astable tone generator. The real complexity was understanding the wiring of a standard elevator call panel, adapting it to battery power, and interfacing the switches to the 7555 module.
This was a good experience for me. Since many interconnections were needed, I learned how to assemble "Molex" push-on connectors.
Several BUCS graduates have shown interest in having their own Light Switch Trainers and I have built a couple of them. I don't do the stands, as I don't have wood-working power tools.
BUCS has recently moved to a larger campus and Dr. Bergin has asked for more specialized electronics and asked me to make a presentation to one of the classes about building Trainer modules.
Possible future projects include:
A module that a non-technical person might build. I am trying to use Home Depot door chimes as a possible solution. The main drawback is that they require connection to the AC power lines.
More powerful audio for a large auditorium setting.
A permanent "hard-wired" set-up connected to the actual light switches in training room. This is a real challenge as I don't want to directly connect to AC wiring at the school. Maybe a photo-electric module?
Identifying radio clubs or computer clubs that might be willing to build and donate modules for graduates who are setting up their own training programs. BUCS graduates are active throughout the USA and in many countries around the world.
It was a strange experience receiving this award at the recent BUCS graduation ceremony … especially as it is named after my wife, who is their "star" volunteer!