diff --git a/lambda/display.c b/lambda/display.c
index cec6e23..2ee0b08 100644
--- a/lambda/display.c
+++ b/lambda/display.c
@@ -24,41 +24,18 @@
 #define MENU_MAX_VALUES 2
 
 uint8_t position = MENU_OFF;
-char* hint = "  ";
-measurement measCur;
+
 measurement measMin = {0, 20, 0, 20, 0, 2000};
 measurement measMax = {0, 0, 0, 0, 0, 0};
 
-/**
- * Cycles through the "menu" (display options) when the menu button is pressed.
- */
-ISR(PCINT0_vect) {
-	if (bit_is_clear(PINB, PB0)) {
-		_delay_ms(30);
-		if (bit_is_clear(PINB, PB0)) {
-			cycle();
-		}
-	}
-}
-
 void cycle(void) {
 	position++;
-	if (position == MENU_MIN_VALUES) {
-		hint = " <";
-		display(measMin);
-	} else if (position == MENU_MAX_VALUES) {
-		hint = " >";
-		display(measMax);
-	} else {
+	if (position > MENU_MAX_VALUES) {
 		position = MENU_OFF;
-		hint = "  ";
-		display(measCur);
 	}
 }
 
 void update(measurement meas) {
-	measCur = meas;
-
 	measMin.tempI = MIN(measMin.tempI, meas.tempI);
 	measMin.tempO = MIN(measMin.tempO, meas.tempO);
 	measMin.lambda = MIN(measMin.lambda, meas.lambda);
@@ -67,21 +44,27 @@
 	measMax.tempO = MAX(measMax.tempO, meas.tempO);
 	measMax.lambda = MAX(measMax.lambda, meas.lambda);
 
-	if (position == MENU_OFF) {
-		display(meas);
+	if (position == MENU_MIN_VALUES) {
+		display(measMin, "  <");
+	} else if (position == MENU_MAX_VALUES) {
+		display(measMax, "  >");
+	} else {
+		display(meas, "   ");
 	}
 }
 
-void display(measurement meas) {
-	uint16_t lambdax100 = divRoundNearest(meas.lambda, 10);
-	div_t lambdaT = div(lambdax100, 100);
-
+void print(measurement meas) {
 	char log[64];
 	snprintf(log, sizeof(log),
-			"Ti %3d C %4u - To %3d C %4u - L %4u %4u %s\r\n",
+			"Ti %3d C %4u - To %3d C %4u - L %4u %4u\r\n",
 			meas.tempI, meas.tempIVoltage, meas.tempO, meas.tempOVoltage,
-			meas.lambda, meas.lambdaVoltage, hint);
+			meas.lambda, meas.lambdaVoltage);
 	printString(log);
+}
+
+void display(measurement meas, char hint[]) {
+	uint16_t lambdax100 = divRoundNearest(meas.lambda, 10);
+	div_t lambdaT = div(lambdax100, 100);
 
 	char line0[17];
 	char line1[17];
diff --git a/lambda/display.h b/lambda/display.h
index fcf1b66..2128f3d 100644
--- a/lambda/display.h
+++ b/lambda/display.h
@@ -15,14 +15,18 @@
 
 /**
  * Updates the measurements, tracks min and max values since last start/reset
- * and displays the current measurements unless the "menu" is active.
+ * and displays the selected measurement values.
  */
 void update(measurement);
 
 /**
- * Formats the given values, displays them on an 16x2 LCD
- * and prints them over USART.
+ * Formats the given measurement values and prints them via USART.
  */
-void display(measurement);
+void print(measurement);
+
+/**
+ * Formats the given measurement values and displays them on an 16x2 LCD.
+ */
+void display(measurement, char[]);
 
 #endif /* DISPLAY_H_ */
diff --git a/lambda/interrupts.c b/lambda/interrupts.c
index c45d7ac..e2f330a 100644
--- a/lambda/interrupts.c
+++ b/lambda/interrupts.c
@@ -15,7 +15,7 @@
 	PORTB |= (1 << PB0);
 
 	// PB1 as output
-	// DDRB |= (1 << PB1);
+	DDRB |= (1 << PB1);
 }
 
 void setupSleepMode(void) {
@@ -27,9 +27,18 @@
 	ADCSRA |= (1 << ADIE);
 
 	// enable PC interrupts
-	PCICR |= (1 << PCIE0);
-	PCMSK0 |= (1 << PB0);
+	// PCICR |= (1 << PCIE0);
+	// PCMSK0 |= (1 << PB0);
+
+	// enable timer 0 overflow interrupt
+	TIMSK0 |= (1 << TOIE0);
 
 	// enable global interrupts
 	sei();
 }
+
+void initTimers(void) {
+	// timer in normal mode is default
+	// timer clock prescaler /64 = 7.8 kHz overflowing every 32 ms
+	TCCR0B |= (1 << CS00) | (1 << CS01);
+}
diff --git a/lambda/interrupts.h b/lambda/interrupts.h
index 2a14296..11efa34 100644
--- a/lambda/interrupts.h
+++ b/lambda/interrupts.h
@@ -23,4 +23,9 @@
  */
 void initInterrupts(void);
 
+/**
+ * Inits the timers.
+ */
+void initTimers(void);
+
 #endif /* INTERRUPTS_H_ */
diff --git a/lambda/lambda.c b/lambda/lambda.c
index 3fe192b..e00635d 100644
--- a/lambda/lambda.c
+++ b/lambda/lambda.c
@@ -18,8 +18,10 @@
  */
 
 #include <stdio.h>
+#include <stdbool.h>
 #include <util/delay.h>
 #include <avr/io.h>
+#include <avr/interrupt.h>
 #include "USART.h"
 #include "lcdroutines.h"
 #include "adc.h"
@@ -28,11 +30,28 @@
 #include "integers.h"
 #include "display.h"
 
+volatile bool buttonPressed = false;
+volatile uint8_t updateCount = 0;
+volatile uint8_t logCount = 0;
+
 /**
- * Initializes the USART transmitter and receiver, the lcd, sets up the ADC
- * and sleep mode and then infinitely measures with a 1 second delay
- * in between.
- * TODO replace delay by a timer?
+ * Called every 16.32 ms.
+ */
+ISR(TIMER0_OVF_vect) {
+	updateCount++;
+	logCount++;
+	if (bit_is_clear(PINB, PB0) && ! buttonPressed) {
+		PORTB ^= (1 << PB1);
+		cycle();
+		buttonPressed = true;
+	} else if (bit_is_set(PINB, PB0)) {
+		buttonPressed = false;
+	}
+}
+
+/**
+ * Does initialization and measures, displays and logs the measurements
+ * infinitely.
  */
 int main(void) {
 	initUSART();
@@ -41,12 +60,19 @@
 	setupADC();
 	setupSleepMode();
 	initInterrupts();
+	initTimers();
 
 	// main loop
 	while (1) {
-		measurement meas = measure();
-		update(meas);
-		_delay_ms(1000);
+		if (updateCount >= 6) {
+			updateCount = 0;
+			measurement meas = measure(); // about 50 ms
+			update(meas); // about 100 ms
+			if (logCount >= 61) {
+				logCount = 0;
+				print(meas); // about 400 ms
+			}
+		}
 	}
 
 	// never reached