2
of the speaker. The amplifier is Class-D, and it is very efficient, so any heat is dissipated through the
PCB layout. It is recommended that the module is securely fitted in a suitable location using the 4 x
adhesive backed pcb standoffs provided in the mounting kit See section 6 for the modules physical
dimensions, connector positions and fixing information.
Alternatively, the module may be mounted using self-adhesive foam pads or with suitable mounting
screws and spacers, but all caution should be taken to ensure that none of the circuit pins or
components on the solder side make contact with any metallic parts.
1.4
Keyboard Switch Assembly Mounting
The keyboard switch assembly is mounted through the speaker housing/enclosure to provide an
easy-to-use interface. The module is supplied with a label to place over the keyboard switch pcb
assembly to make the installation look professional.
When the enclosure is thick enough the keyboard assembly is retained using an M2.5 x 20mm
Countersink screw (supplied), which is hidden by the label, see figure 3 above. Do not over-tighten
the mounting screw.
If the enclosure is too thin to use a countersunk screw (such as fitting into sheet metal), then an
Instrument Head type screw may be used. In this instance the label needs to be cut out to allow the
screw head to pass through from the outside. This can easily be achieved by applying the label to
the screw hole and carefully cutting around the screw hole using a scalpel or craft knife. Again, do
not over-tighten the screw.
1.5
Sounder Mounting (not fitted as standard)
If a sounder is to be used instead of the internal audio tones, Mount the sounder in a suitable
position using a double side sticky foam pad (not supplied).
Do not cover the small hole in the face of the sounder. For best results mount the sounder where it
can radiate sound to the outside face of the case, for example behind an air vent.
1.6
DSP Noise cancellation
The bhi DSP noise cancelling processes the incoming signal and differentiates the speech from the
noise. The unwanted noise and interference are attenuated to leave only speech. The following
diagrams are taken from actual audio signals and illustrate how the signal the signal looks before
and after processing.
Figure 3 - Noise Reduction
