generate MIDI pitch lookup table

.gitignore

@@ -1,2 +1,3 @@
 .vscode
-out
+out
+pitch_table.h

Makefile

@@ -88,7 +88,7 @@ endef
 	mkdir -p .vscode
 	sed '[email protected][email protected]$(call to-json-array, ${AVR_INC} ${VPATH} ${VARIANTS})@' c_cpp_properties.json.template > .vscode/c_cpp_properties.json
 
-.PHONY: all clean upload vscode
+.PHONY: all clean upload vscode pitch_table
 
 all: ${BUILD_DIR}/${PROGRAM}.hex
 
@@ -103,4 +103,7 @@ endif
 
 vscode:
 	rm -rf .vscode/c_cpp_properties.json
-	make .vscode/c_cpp_properties.json
+	make .vscode/c_cpp_properties.json
+
+pitch_table:
+	python gen_pitch_table.py > pitch_table.h

gen_pitch_table.py

@@ -0,0 +1,37 @@
+#!/usr/bin/env python3
+
+start_pitch = 36 # C2
+end_pitch = 84 # C6
+
+pitch_A0 = 21
+pitch_C1 = 24
+pitch_A4 = 69
+freq_A4 = 440
+
+def pitch_to_freq(pitch):
+    dist_A4 = pitch - pitch_A4
+    factor = pow(2, abs(dist_A4) / 12)
+    
+    if dist_A4 > 0:
+        return freq_A4 * factor
+    else:
+        return freq_A4 / factor
+
+def pitch_to_period_micros(pitch):
+    return 1 / pitch_to_freq(pitch) * 1000 * 1000
+
+pitch_names = ["A", "A#", "B", "C", "C#", "D", "D#", "E", "F", "F#", "G", "G#"]
+def pitch_to_name(pitch):
+    return pitch_names[(pitch - pitch_A0) % 12] + str(int((pitch - pitch_C1) / 12) + 1)
+
+print("#pragma once")
+print("")
+print("constexpr unsigned int midi_pitch_offset = " + str(start_pitch) + ";")
+print("constexpr unsigned int midi_pitch_max = " + str(end_pitch) + ";")
+print("constexpr unsigned long midi_pitch_period[" + str(end_pitch - start_pitch) + "] = {")
+
+for i in range(start_pitch, end_pitch):
+    period = int(pitch_to_period_micros(i))
+    print("    " + str(period) + ",\t// " + pitch_to_name(i))
+
+print("};")

main.cpp

@@ -33,25 +33,15 @@ int main() {
         motors[i].Init();
     }
 
-    // Test: play A4 (440 Hz) on each successive motor every second
-    int cur_motor = -1;
+    // Test: play a C chord
+    motors[0].TickAtPitch(60); // C4
+    motors[1].TickAtPitch(64); // E4
+    motors[2].TickAtPitch(67); // G4
 
     while (true) {
         unsigned long cur_micros = micros();
 
         handle_tick(cur_micros);
-
-        int new_motor = (cur_micros / 1000 / 1000) % 4;
-        
-        if (new_motor != cur_motor) {
-            motors[new_motor].TickOn(2272);
-
-            if (cur_motor != -1) {
-                motors[cur_motor].TickOff();
-            }
-
-            cur_motor = new_motor;
-        }
     }
 
     return 0;

motor_control.cpp

@@ -1,5 +1,6 @@
 #include <Arduino.h>
 #include "motor_control.h"
+#include "pitch_table.h"
 
 MotorControl::MotorControl(int pin_dir, int pin_step) :
     pin_dir(pin_dir), pin_step(pin_step),
@@ -22,6 +23,15 @@ void MotorControl::TickOn(unsigned long period_micros) {
     last_tick_micros = 0;
 }
 
+void MotorControl::TickAtPitch(unsigned int midi_pitch) {
+    // Bounds check
+    if (midi_pitch < midi_pitch_offset || midi_pitch >= midi_pitch_max) {
+        return;
+    }
+    
+    TickOn(midi_pitch_period[midi_pitch - midi_pitch_offset]);
+}
+
 void MotorControl::TickOff() {
     tick_period_micros = 0;
 }

motor_control.h

@@ -17,6 +17,8 @@ class MotorControl {
         void Init();
         // Set the motor to tick at a given interval (inverse of frequency)
         void TickOn(unsigned long period_micros);
+        // Set the motor to tick with a given MIDI pitch
+        void TickAtPitch(unsigned int midi_pitch);
         // Turn off the motor
         void TickOff();
         // Perform a tick if necessary