Microchip Technology DM300024 Data Sheet
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.
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.
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:
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.
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