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4.5 Noise Reduction On/Off
The module has the provision for remotely enabling and disabling the noise reduction, while in
operation. The default setting for the module is noise reduction ON. This may be switched by the use
of the noise cancellation On/Off pin (PL2 pin 8). To inhibit noise reduction, connect this pin to 0V. To
enable the noise reduction, leave the pin unconnected.
The module may be controlled with a microprocessor. As the 1901 Module employs internal pull-
ups, it is not necessary to drive the microprocessor port pins high, they can be placed in a high
impedance state.
It should be noted that the 1901 module operates with 3.3 Volt logic signals. Therefore, if it is
intended that the Microprocessor is to drive the 1901 lines High, the Microprocessor should be
operating from a 3.3 Volt supply as well. Alternatively, the control signals may be attenuated using a
simple potential divider as discussed in section 5.
5. Application Notes
5.1 Noise Cancellation On/Off with indication
In the example opposite a
Tricolour (or separate Red and
Green) LED’s are used to give a
visual indication of the Noise
Reduction mode. The Green
LED will illuminate when the
Noise Reduction is On and the
Red will illuminate when the
Noise Reduction is Off.
Figure 7. Noise Reduction On/Off with Red/Green LED Status indicator
5.2 Remote adjustment of Noise Reduction level
This section illustrates the various options for altering the DSP level remotely, during operation.
Figure 8. Basic setting using a BCD switch with complementary logic.
