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ad7172: Correct postfilter rates and rejection

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The AD7172-2 Rev. A datasheet is inconsistent on the 50/60 Hz postfilter
rates and rejection figures between the *ENHANCED 50 Hz AND 60 Hz
REJECTION FILTERS* and the *FILTER CONFIGURATION REGISTER 0* sections.
Use the former section's figures instead.

The latter section is wrong since the 21.25 SPS figure is incorrect, as
the output data rate = 1 / (settling time), and 1 / (40 ms) = 25 Hz.
This seems to have been corrected in the datasheets for the rest of the
AD717x family, which have the same filter.
This commit is contained in:
atse 2025-01-27 12:40:40 +08:00
parent 9868ca4447
commit 81112e429b
2 changed files with 27 additions and 14 deletions
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8
README.md
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@ -170,10 +170,10 @@ postfilter rate can be tuned with the `postfilter` command.
| Postfilter rate | Rejection | Effective sampling rate |
| --- | :---: | --- |
| 16.67 Hz | 92 dB | 8.4 Hz |
| 20 Hz | 86 dB | 9.1 Hz |
| 21.25 Hz | 62 dB | 10 Hz |
| 27 Hz | 47 dB | 10.41 Hz |
| 16.667 Hz | 90 dB | 8.4 Hz |
| 20 Hz | 85 dB | 9.1 Hz |
| 25 Hz | 62 dB | 10 Hz |
| 27.27 Hz | 47 dB | 10.41 Hz |
## Thermo-Electric Cooling (TEC)

33
src/ad7172/mod.rs
View File

@ -145,22 +145,35 @@ impl fmt::Display for RefSource {
#[derive(Clone, Copy, Debug, PartialEq, Serialize, Deserialize)]
#[repr(u8)]
/// Simultaneous Rejection of 50 Hz +/- 1 Hz and 60 Hz +/- 1 Hz
pub enum PostFilter {
/// 27 SPS, 47 dB rejection, 36.7 ms settling
/// Output Data Rate: 27.27 SPS,
/// Settling Time: 36.67 ms,
/// Rejection: 47 dB
F27SPS = 0b010,
/// 21.25 SPS, 62 dB rejection, 40 ms settling
F21SPS = 0b011,
/// 20 SPS, 86 dB rejection, 50 ms settling
/// Output Data Rate: 25 SPS,
/// Settling Time: 40.0 ms,
/// Rejection: 62 dB
F25SPS = 0b011,
/// Output Data Rate: 20 SPS,
/// Settling Time: 50.0 ms,
/// Rejection: 85 dB
F20SPS = 0b101,
/// 16.67 SPS, 92 dB rejection, 60 ms settling
/// Output Data Rate: 16.667 SPS,
/// Settling Time: 60.0 ms,
/// Rejection: 90 dB
F16SPS = 0b110,
Invalid = 0b111,
}
impl PostFilter {
pub const VALID_VALUES: &'static [Self] = &[
PostFilter::F27SPS,
PostFilter::F21SPS,
PostFilter::F25SPS,
PostFilter::F20SPS,
PostFilter::F16SPS,
];
@ -182,10 +195,10 @@ impl PostFilter {
/// Samples per Second
pub fn output_rate(&self) -> Option<f32> {
match self {
PostFilter::F27SPS => Some(27.0),
PostFilter::F21SPS => Some(21.25),
PostFilter::F27SPS => Some(27.27),
PostFilter::F25SPS => Some(25.0),
PostFilter::F20SPS => Some(20.0),
PostFilter::F16SPS => Some(16.67),
PostFilter::F16SPS => Some(16.667),
PostFilter::Invalid => None,
}
}
@ -195,7 +208,7 @@ impl From<u8> for PostFilter {
fn from(x: u8) -> Self {
match x {
0b010 => PostFilter::F27SPS,
0b011 => PostFilter::F21SPS,
0b011 => PostFilter::F25SPS,
0b101 => PostFilter::F20SPS,
0b110 => PostFilter::F16SPS,
_ => PostFilter::Invalid,