Add calibration code

flake.nix

@@ -284,6 +284,30 @@
           ];
         };
 
+      packages."x86_64-linux"."touch-sensor_" = 
+      let
+        pkgs = import nixpkgs { system = "x86_64-linux"; };
+        avr = pkgs.pkgsCross.avr.buildPackages;
+      in packages."x86_64-linux"."touch-sensor" { gcc = "${avr.gcc}/bin/avr-gcc"; cflags = mcu_cflags attiny85; avr = true; };
+      packages."x86_64-linux"."touch-sensor" =
+        { gcc, cflags, avr }:
+        let
+          pkgs = import nixpkgs { system = "x86_64-linux"; };
+        in mkProgram {
+          pkgs = pkgs;
+          gcc = gcc;
+          cflags = cflags;
+          pname = "touch-sensor";
+          psrc = ./touch-sensor;
+          inherit avr;
+
+          pbuildInputs = [
+            (packages."x86_64-linux"."dio" { inherit gcc cflags; })
+            (packages."x86_64-linux"."display" { inherit gcc cflags; })
+            (packages."x86_64-linux"."shift-register" { inherit gcc cflags; })
+          ];
+        };
+
       devShell."x86_64-linux" =
         let
           pkgs = import nixpkgs { system = "x86_64-linux"; };

touch-sensor/main.c

@@ -0,0 +1,94 @@
+#include <dio.h>
+#include <stdio.h>
+#include <display.h>
+
+uint32_t read_capacitance(dio_t *dio) {
+    uint32_t i;
+
+    dio_set_direction(dio, LINE_OUT);
+    dio_set(dio, 1);
+
+    i = 0;
+    dio_set_direction(dio, LINE_IN);
+    while (dio_read(dio) > 0) i++;
+    return i;
+}
+
+uint32_t calibrate(dio_t *dio) {
+    uint32_t max = 0;
+
+    for (uint8_t i = 0; i < 100; i++) {
+        uint8_t cap = read_capacitance(dio);
+        max = cap > max ? cap : max;
+        _delay_ms(10);
+    }
+
+    return max;
+}
+
+int main(void) {
+    dio_t sensor = (dio_t){ .ddr = &DDRB, .port = &PORTB, .pin = &PINB, .addr = 0 };
+    display_t display = {
+        .reg = {
+            .output         = { .ddr = &DDRB, .port = &PORTB, .pin = &PINB, .addr = 4 },
+            .shift_clock    = { .ddr = &DDRB, .port = &PORTB, .pin = &PINB, .addr = 3 },
+            .latch_clock    = { .ddr = &DDRB, .port = &PORTB, .pin = &PINB, .addr = 2 },
+        },
+    };
+    display_init(&display);
+
+    display_enable(&display);
+    display_clear(&display);
+
+    // calibration
+    //
+    // 100 times:
+    //  Output 1
+    //  Switch to Input
+    //  measure in a loop until the input is 0
+    //  save the measurement
+    //
+    // normal function
+    //  Output 1
+    //  Switch to input
+    //  measure in a loop until the input is 0
+    //  check against the saved measurement
+    //  enable pin if significantly higher than the saved measurement
+    //  update the average
+
+    MCUCR |= _BV(PUD);
+
+
+    uint8_t calibration_countdown = 0;
+    uint32_t calibration = 0;
+    bool touch = false;
+    while (1) {
+        if (calibration_countdown == 0 && !touch) {
+            calibration = calibrate(&sensor);
+            calibration_countdown = 100;
+
+            char msg[20];
+            snprintf(msg, 20, "calib: %6ld", calibration);
+            display_set_location(&display, 0, 0);
+            display_write_message(&display, msg);
+        }
+
+        uint32_t cap = read_capacitance(&sensor);
+
+        if (cap > calibration) {
+            display_set_location(&display, 1, 0);
+            display_write_message(&display, "touch!");
+            touch = true;
+        } else if (touch) {
+            display_set_location(&display, 1, 0);
+            display_write_message(&display, "      ");
+            touch = false;
+        }
+
+        if (calibration_countdown > 0) {
+            calibration_countdown--;
+        }
+        _delay_ms(100);
+    }
+
+}