Page 10
The transistors allow
interfacing with higher
voltages to control the DSP
level. As a rough guide the
Resistors R1, R3, R5 can be
around 10 kOhm. Resistors
R2, R4 and R6 could be in
the range 2.2 kOhm for
control voltages over 10
Volts and 4.7 kOhm for
voltages between 5 Volts
and 10 Volts.
Figure 9. Noise Reduction setting using a Transistors
The module can be controlled with a
microcontroller. It is not necessary to
drive the control pins with the controller
as the NEDSP has internal pull-up
resistors. Therefore, the microcontroller
would operate pulling Low or in a High
impedance state.
Figure 10
–
Operation with a Microcontroller
Important Note:
If the Microcontroller is driving the control pins both High and Low, it should be
operate from a 3.3 Volt supply only. If this can’t be achieved, then consider using either the
Transistor method of interfacing above or the much simpler voltage divider method outlines for 5
Volt operation shown in Figure 11.
If a Microcontroller
operating on 5 Volts is to
be used to drive the
NEDSP1901 control pins,
make sure that the drive
voltage is no higher than
3.3 Volts. Alternatively, if
the Microcontroller is
operating on 5 Volts,
insert a simple Voltage
divider circuit between
the control pins and the
microcontroller.
Figure 11. Alternative method of controlling the NEDSP1901 with 5 Volt logic.
For +5 Volts, the suggested values for R1, R3 and R5 is 1 kOhm, while R2, R4 and R6 should be 1.5
kOhm.
