Results of Design
The security system responds nicely to zone violations from vibration sensors, hall sensors, and IR sensors by slewing the camera accordingly and reporting the violation. The slewing in the vertical dimension is a bit inhibited by the extra torque needed to overcome friction with the wooden supports and the weight of the horizontal positioning motor. All wooden parts were cut and assembled to the best of our ability with such precise tools as Swiss army knives and Dremel sanders and imperfections in the construction made it hard work for vertical positioning. The stepper motor step angle of 7.5 degrees, while ideal for a large room is not appropriate for a test board of dimension ~ 4' X 3'. Vertical motion of the camera therefore is not necessary when all sensors are at close range.
The precision of the RhythmPrint technology was set to 20ms based on the response time and measured repeatability of the standard user (i.e. Aaron and Fran). In our estimation, with the help of the guide LED, the entered beat pattern of the disarm code can be repeatable to within 40ms with practice. The window of acceptable beat error is adjustable by changing the assemble defined variable, tolerance which is currently set to 30. This means that the user can be off in timing of any given digit press by as much as 30X20ms or 600ms and still disarm the system with the correct code.
In the construction of this project, special attention was given to safety. Our two motors that required a total of 8W of power were carefully isolated from the circuit with their own high voltage supply. The analog circuitry and digital circuitry also ran on a five volt supply but we used the lower power STK500 supplied VCC rail for it to make it safer to probe points in the circuit. When not doing tests specific to the motors, the high voltage supply was powered down. Another safety feature of the demonstration board that was constructed is the mechanical motor stop that prevents the horizontal stepper motor and dowel assembly from falling from the support or violently swinging downward if suddenly powered down. We also made sure not to include any killer robot code in the firmware for this project.
The tradeoff in adding an extra layer of password protection with RhythmPrint is its unfamiliarity to the users. For the first few times it may be challenging to remember the beat pattern by which you must enter your code. Because of this, we have added additional features to make it easier to get the timing correct. A 1Hz guide beat is shown visually to the user on a red system LED. Operators are encouraged to synchronize at least their first digit with one of these guide beats. When the alarm system is armed (or in teach new code mode), the system LED blinks at a rate of .25Hz (once every 4 seconds with 50% duty cycle). After the start button is pressed (‘D'), which starts the beat counter, the LED blink rate switches to 1Hz. We have found that the transition in the blink frequency clearly marks the starting of the timer and draws attention to the guide beats much more so than if the LED transitions from solid on to a 1Hz blink.
A second feature of the Eye in the Sky security system is the ability of the users to add additional sensors or to re-arrange existing ones and teach the motors where they are placed themselves. As long as the sensors plugged into the system contain all the analog circuitry necessary to do the analog to digital conversion, the sensor module can add directly onto a free input pin and the AND gate feeding into the external interrupt.
In the project's present form, it is still in a proof of concept phase where many different cables from each sensor need to be tied into the central analog circuitry (on a whiteboard) which interfaces with the microcontroller with four port dongles. To improve its usability for others, the sensors would be coupled with their analog circuitry and made into plug-in modules. The modules all connect to a jack that mates them to the necessary port pins and interrupt logic.