Device Description (Original Description)
“Voice Activated Relay (2002)
The device should be constructed to interface with a microphone
that will received audio signals (human voice). The microphone
signal should trigger the voice-activated relay, which is
also interfaced with a Macintosh computer mouse. The activation
of the relay causes an electrical signal to be sent to the
mouse, simulating a mouse click. The voice-activated relay
should have at least one and possibly two adjustment controls.
One control is for sensitivity--this control is essential.
It determines how intense the audio signal must be before
the relay will detect the signal. The other control, which
would be useful but is not essential, establishes a refractory
period (i.e., how long the relay will remain inactive after
detecting a signal); this control will prevent the relay
from sending a continuous stream of signals to the computer
mouse if the audio input consists of a continuous sound
rather than a very brief signal.”
As a result of a meeting with Mike Mason (Jan 14, 2004),
several changes were made to the above description. The
device that we are designing/ building will be powered completely
by a USB connection and attached to a USB mouse that has
both Mac and PC drivers. Secondly, the device will be made
compatible with both the G4 series (and new) versions of
Mac computers, and compatible with the latest PC’s.
Often the response time is very important, therefore, an
adjustable triggered time option will be added to the design.
An on/off switch will also be added to the device, as well
as another switch that will switch between “double
click” mode and “single click” mode. LED’s
will be will be added to give the user feedback on the state
of the device.
THE PROJECT FROM THE USER’S POINT OF VIEW
The device will appear as shown in the following
diagram:
The green LED will turn on when the sound level has reached
the appropriate threshold level and the red LED will turn
on when the relay has been triggered. The red LED will remain
on until the reset time has been reached.
- There are three dials on the device:
- Dial 1: controls the sensitivity of the device to sound
input
- Dial 2: controls the triggering time
- Dial 3: controls the reset time
PROJECT FROM THE DESIGNERS POINT OF VIEW
The three dials will be attached to potentiometers and
the values will be read through A/D converters to a micro
controller. The voltage will be divided into 5-10 discrete
values, which will translate to a semi-exponential scale
on the dials themselves.
We considered whether to use a microcontroller or analogue
circuitry to build the device. We chose the microcontroller
in order reduce part count, therefore, making the device
cheaper to construct.
The PIC18F248A microcontroller was chosen because it meets
the necessary design requirementsand it also has a MAD function that would be used extensively for the software filter.
An OP amp-resistor-capacitor
bandpass filter was created to prefilter the signal before it goes to
the PIC.
