diff --git a/dosimeter.cpp b/dosimeter.cpp
new file mode 100644
index 0000000..4c0b7d1
--- /dev/null
+++ b/dosimeter.cpp
@@ -0,0 +1,71 @@
+#include "dosimeter.h"
+
+#include "Arduino.h"
+
+DosimeterType Dosimeter;
+
+static float getCalibrationFactor(int type) {
+    switch(type) {
+        case J305:
+        case M4011:
+            return 0.0065;
+            break;
+        default:
+            return NAN;
+    }
+}
+
+int type;
+volatile int buckets[BUCKETS_PER_MINUTE] = {0};
+int last = 0;
+bool valid = false;
+
+static inline void clearISR() {
+    unsigned long gpio_status = GPIO_REG_READ(GPIO_STATUS_ADDRESS);
+    GPIO_REG_WRITE(GPIO_STATUS_W1TC_ADDRESS, gpio_status);
+}
+
+static void ICACHE_RAM_ATTR isr() {
+    int next = (millis() / BUCKET_WIDTH_IN_MS) % BUCKETS_PER_MINUTE;
+
+    if (last != next) {
+        for (int i = (last + 1) % BUCKETS_PER_MINUTE; i != next; i = (i + 1) % BUCKETS_PER_MINUTE) {
+            buckets[i] = 0;
+        }
+
+        buckets[next] = 1;
+        last = next;
+    } else {
+        buckets[next]++;
+    }
+
+    clearISR();
+}
+
+void DosimeterType::begin(int pin, int _type) {
+    type = _type;
+
+    pinMode(pin, INPUT);
+    attachInterrupt(digitalPinToInterrupt(pin), isr, RISING);
+}
+
+int DosimeterType::getCPM() {
+    int result = 0;
+    for (int i = 0; i < BUCKETS_PER_MINUTE; i++) {
+        result += buckets[i];
+    }
+    return result;
+}
+
+float DosimeterType::getEquivalentDoseRate() {
+    return getCPM() * getCalibrationFactor(type);
+}
+
+bool DosimeterType::isValid() {
+    if (valid) {
+        return true;
+    } else {
+        valid = millis() > (60l * 1000);
+        return valid;
+    }
+}
diff --git a/dosimeter.h b/dosimeter.h
new file mode 100644
index 0000000..3fa982a
--- /dev/null
+++ b/dosimeter.h
@@ -0,0 +1,23 @@
+#ifndef _DOSIMETER_H_
+#define _DOSIMETER_H_
+
+#define M4011 (1)
+#define J305  (2)
+
+#define BUCKETS_PER_MINUTE (60)
+#define BUCKET_WIDTH_IN_MS ((60l * 1000) / BUCKETS_PER_MINUTE)
+
+class DosimeterType {
+public:
+    void begin(int pin, int type);
+
+    bool isValid();
+
+    float getEquivalentDoseRate();
+    int getCPM();
+private:
+};
+
+extern DosimeterType Dosimeter;
+
+#endif
diff --git a/examples/example.ino b/examples/example.ino
new file mode 100644
index 0000000..5c43fb7
--- /dev/null
+++ b/examples/example.ino
@@ -0,0 +1,30 @@
+#include <dosimeter.h>
+
+#define TUBE_PIN (4)
+
+void setup() {
+  Serial.begin(9600);
+
+  Dosimeter.begin(TUBE_PIN, J305);
+}
+
+void loop() {
+  Serial.print("CPM: ");
+  Serial.print(Dosimeter.getCPM());
+  if (Dosimeter.isValid()) {
+    Serial.println();
+  } else {
+    Serial.println(" (invalid)");
+  }
+  
+  Serial.print("dose rate: ");
+  Serial.print(Dosimeter.getEquivalentDoseRate());
+  Serial.print(" µSv/h");
+  if (Dosimeter.isValid()) {
+    Serial.println();
+  } else {
+    Serial.println(" (invalid)");
+  }
+  
+  delay(1000);
+}