dsPICDEM™ 1.1 Plus Development Board User’s Guide
DS70099D-page 32
©
2006 Microchip Technology Inc.
3.3.1.2
DSP OPERATIONS MODE
From the Menu Options display, pressing switch SW3 launches the DSP Operations
demo, which displays the digital signal values shown in Figure 3-6. This display
provides information on the various signal processing operations that are performed on
the signal at analog input pin, AN3.
FIGURE 3-6:
DSP OPERATIONS DISPLAY
The DSP operations display shows several parameters for a sampled sine-wave
signal. A fundamental sine-wave signal is generated by stepping the MCP41010 digital
potentiometer (U8) output at an 8 kHz rate. The output of the digital potentiometer is
applied to a Low-Pass (LP) filter with a cutoff frequency of approximately 4 kHz. This
LP filter removes the high-frequency components and yields a sine wave adequate for
this demonstration. Five frequencies are developed and selected by varying
potentiometer RP1, as shown in Table 3-1.
TABLE 3-1:
FREQUENCIES VS. POTENTIOMETER SETTING
The filtered output of the MCP41010 is routed to pin AN3/RB3, which is an input to the
12-bit ADC. The ADC collects 256 samples from the MCP41010 at an 8 kHz sample
rate. These samples are optionally subjected to a digital filtering algorithm. The
following three digital filtering options are provided and selected by switch SW2:
• None
• Infinite Impulse Response (IIR)
• Finite Impulse Response (FIR)
Subsequently, their spectral components are estimated. The frequency estimate of the
signal on pin AN3/RB3 is displayed on the first row of the DSP Operations display.
Potentiometer Setting
Resulting Frequency
0
≤
RP1
≤
1V
100 Hz
1
≤
RP1
≤
2V
500 Hz
2
≤
RP1
≤
3V
1000 Hz
3
≤
RP1
≤
4V
1500 Hz
4
≤
RP1
≤
5V
2000 Hz
F = 1000
B
IN
= 032
256
PT
T
FFT
=018175
CY
I I R
T
FILT
=028649
CY
MAIN
– s1
CHNGFILT
–
S
2
Содержание dsPICDEM 1.1 Plus
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