From ef4c18417684920726edaa6d0d01c85acc3a0abd Mon Sep 17 00:00:00 2001
From: "Matthias P. Braendli" <matthias.braendli@mpb.li>
Date: Wed, 17 Feb 2021 21:46:29 +0100
Subject: Calibrate S meter

---
 sw/picardy/src/main.rs | 37 +++++++++++++++++++++++++++++--------
 sw/picardy/src/ui.rs   |  4 ++--
 2 files changed, 31 insertions(+), 10 deletions(-)

diff --git a/sw/picardy/src/main.rs b/sw/picardy/src/main.rs
index a6a3e4a..22b894b 100644
--- a/sw/picardy/src/main.rs
+++ b/sw/picardy/src/main.rs
@@ -292,14 +292,8 @@ fn main() -> ! {
         }
         previous_vfo = vfo;
 
-        let s_meter_value: u16 = adc2.read(&mut s_meter).unwrap();
-
-        // Avoid 0 because of log10
-        let s_meter_value = f32::from(if s_meter_value == 0 { 1 } else { s_meter_value });
-
-        // ADC is 12-bit, convert to dB full-scale
-        let s_meter_value = 10f32 * log10f::log10f(f32::from(s_meter_value) / 4092f32);
-        let s_meter_value = s_meter_value as i32;
+        let s_meter_adc_value: u16 = adc2.read(&mut s_meter).unwrap();
+        let s_meter_value = s_meter_from_adc(s_meter_adc_value);
         let t_now = ticks_now();
         if last_s_meter_update_time + 10 < t_now {
             update_disp_required = s_meter_value != last_s_meter_value;
@@ -322,6 +316,33 @@ fn main() -> ! {
     }
 }
 
+fn s_meter_from_adc(adc : u16) -> u8 {
+    // Avoid 0 because of log10
+    let adc = f32::from(if adc == 0 { 1 } else { adc });
+    // ADC is 12-bit, convert to dB full-scale
+    let adc_db = 10f32 * log10f::log10f(adc / 4092f32);
+
+    /* Hand-calibrated lookup table */
+    if adc_db <= -35f32 {
+        1
+    }
+    else if adc_db <= -20f32 {
+        4
+    }
+    else if adc_db <= -12f32 {
+        5
+    }
+    else if adc_db <= -8f32 {
+        6
+    }
+    else if adc_db <= -7f32 {
+        7
+    }
+    else {
+        9
+    }
+}
+
 #[interrupt]
 fn TIM2() {
     let timer = unsafe { &mut *CLOCK_TIMER.as_mut_ptr() };
diff --git a/sw/picardy/src/ui.rs b/sw/picardy/src/ui.rs
index 9d5a4e4..0170813 100644
--- a/sw/picardy/src/ui.rs
+++ b/sw/picardy/src/ui.rs
@@ -278,7 +278,7 @@ impl UI {
     }
 }
 
-pub fn update_disp<T: hd44780_driver::bus::DataBus>(lcd: &mut HD44780<T>, state: &State, delay: &mut Delay, s_meter_value: i32, bfo_tune_fail: bool)
+pub fn update_disp<T: hd44780_driver::bus::DataBus>(lcd: &mut HD44780<T>, state: &State, delay: &mut Delay, s_meter_value: u8, bfo_tune_fail: bool)
 {
     let mut string = arrayvec::ArrayString::<[_; 16]>::new();
 
@@ -298,7 +298,7 @@ pub fn update_disp<T: hd44780_driver::bus::DataBus>(lcd: &mut HD44780<T>, state:
 
     if string.len() <= 16 - 4 {
         // Avoids crash when frequency is very negative
-        write!(string, "S{:3}", s_meter_value).unwrap();
+        write!(string, " S{:1}", s_meter_value).unwrap();
     }
 
     lcd.set_cursor_pos(0, delay).unwrap();
-- 
cgit v1.2.3