From 135537ec2f0fa680752f3585f54d510ad79984ab Mon Sep 17 00:00:00 2001
From: "Tanner Collin (aider)" <git@tannercollin.com>
Date: Thu, 5 Jun 2025 11:24:16 -0600
Subject: [PATCH] feat: Filter RPM jitter caused by single pulse drops

---
 tach/tach.ino | 36 +++++++++++++++++++++++++++++++++++-
 1 file changed, 35 insertions(+), 1 deletion(-)

diff --git a/tach/tach.ino b/tach/tach.ino
index e120caa..0458045 100644
--- a/tach/tach.ino
+++ b/tach/tach.ino
@@ -16,6 +16,10 @@ volatile unsigned long g_isr_pulse_count_total = 0; // ISR increments this conti
 unsigned long g_main_last_pulse_count_snapshot = 0; // Main loop stores previous snapshot here
 unsigned long last_measurement_time = 0;
 
+// --- RPM Display Filtering Variables ---
+int g_rpm_value_on_display = 0; // Stores the last RPM value shown on the 7-segment display by the loop
+bool g_is_first_rpm_calc_in_loop = true; // Flag to handle the first RPM calculation
+
 // --- Interrupt Service Routine (ISR) ---
 void count_pulse() {
   g_isr_pulse_count_total++;
@@ -76,7 +80,37 @@ void loop() {
     }
     int rpm = (int)rpm_float;
 
-    show(rpm);
+    // RPM Filtering Logic
+    if (g_is_first_rpm_calc_in_loop) {
+        show(rpm);
+        g_rpm_value_on_display = rpm;
+        g_is_first_rpm_calc_in_loop = false;
+    } else {
+        if (rpm == 0 && g_rpm_value_on_display != 0) {
+            // If RPM is actually zero, update the display to show zero
+            show(rpm);
+            g_rpm_value_on_display = rpm;
+        } else if (rpm != 0) { // Apply jitter filter only if current rpm is not zero
+            float rpm_float_if_one_more_pulse = 0.0;
+            if (actual_elapsed_time > 0) { // Avoid division by zero
+                rpm_float_if_one_more_pulse = ( (float)(collected_pulses + 1) / PULSES_PER_REVOLUTION ) * (60000.0 / actual_elapsed_time);
+            }
+            int rpm_if_one_more_pulse = (int)rpm_float_if_one_more_pulse;
+
+            // Check for the specific 1-pulse drop jitter
+            if (rpm < g_rpm_value_on_display && rpm_if_one_more_pulse == g_rpm_value_on_display) {
+                // Jitter detected (e.g., displayed 6000, current calc is 5925, but 5925 with +1 pulse would be 6000)
+                // Do not update the display; keep showing g_rpm_value_on_display.
+                Serial.print("Filtered (jitter) RPM: "); Serial.print(rpm);
+                Serial.print(" -> Kept displaying: "); Serial.println(g_rpm_value_on_display);
+            } else {
+                // Not a jitter, or a rise, or a larger drop. Update display.
+                show(rpm);
+                g_rpm_value_on_display = rpm;
+            }
+        }
+        // If rpm is 0 and g_rpm_value_on_display is already 0, do nothing to avoid redundant show(0)
+    }
 
     // Debugging output
     Serial.print("Pulses: "); Serial.print(collected_pulses);