diff --git a/application.c b/application.c
index d888ff7..d5ec347 100644
--- a/application.c
+++ b/application.c
@@ -26,6 +26,7 @@
 #include <libopencm3/stm32/desig.h> // design utilities
 #include <libopencm3/stm32/flash.h> // flash utilities
 #include <libopencm3/stm32/adc.h> // ADC utilities
+#include <libopencm3/stm32/timer.h> // timer library
 
 /* own libraries */
 #include "global.h" // board definitions
@@ -73,6 +74,9 @@ static const uint32_t channel_pins[] = {GPIO_PIN(PB12), GPIO_PIN(PB13), GPIO_PIN
 static uint8_t channel_start = 0; /**< first signal of range to probe */
 static uint8_t channel_stop = CHANNEL_NUMBERS - 1; /**< last signal of range to probe */
 
+/** timer ID for timer to measure activity timing */
+#define MONITOR_TIMER 2
+
 size_t putc(char c)
 {
 	size_t length = 0; // number of characters printed
@@ -428,6 +432,18 @@ static void command_monitor(void* argument)
 	}
 	puts("\n");
 
+	// setup timer to measure milliseconds
+	rcc_periph_clock_enable(RCC_TIM(MONITOR_TIMER)); // enable clock for timer peripheral
+	rcc_periph_reset_pulse(RST_TIM(MONITOR_TIMER)); // reset timer state
+	timer_disable_counter(TIM(MONITOR_TIMER)); // disable timer to configure it
+	timer_set_mode(TIM(MONITOR_TIMER), TIM_CR1_CKD_CK_INT, TIM_CR1_CMS_EDGE, TIM_CR1_DIR_UP); // set timer mode, use undivided timer clock, edge alignment (simple count), and count up
+	timer_set_prescaler(TIM(MONITOR_TIMER), (rcc_ahb_frequency / 2000) - 1); // generate half millisecond ticks (prescaler is not large enough for milliseconds)
+	timer_set_period(TIM(MONITOR_TIMER), 2000 - 1); // set period to seconds
+	timer_clear_flag(TIM(MONITOR_TIMER), TIM_SR_UIF); // clear update (overflow) flag
+	timer_update_on_overflow(TIM(MONITOR_TIMER)); // only use counter overflow as UEV source (use overflow as start time or timeout)
+	uint32_t seconds = 0; // count the seconds using the overflow
+	timer_enable_counter(TIM(MONITOR_TIMER)); // enable timer
+
 	// start monitoring
 	uint16_t gpioa_data = UINT16_MAX;
 	uint16_t gpiob_data = UINT16_MAX;
@@ -438,12 +454,17 @@ static void command_monitor(void* argument)
 			wakeup_flag = false; // clear flag
 			second_flag = false; // clear flag
 		}
+		// one second has passed
+		if (timer_get_flag(TIM(MONITOR_TIMER), TIM_SR_UIF)) {
+			timer_clear_flag(TIM(MONITOR_TIMER), TIM_SR_UIF); // clear flag
+			seconds++; // count the second
+		}
 		// check is there is a change on a channel
 		const uint16_t gpioa_new = gpio_get(GPIOA, gpioa_mask);
 		const uint16_t gpiob_new = gpio_get(GPIOB, gpioa_mask);
 		if (gpioa_new != gpioa_data || gpiob_new != gpiob_data) {
 			// print data
-			puts("0000.000");
+			printf("%04u.%03u", seconds, timer_get_counter(TIM(MONITOR_TIMER)) / 2);
 			for (uint8_t i = channel_start; i <= channel_stop; i++) {
 				const uint16_t port = (GPIOA == channel_ports[i] ? gpioa_new : gpiob_new);
 				const uint8_t high = ((port & channel_pins[i]) ? 1 : 0);
@@ -462,10 +483,13 @@ static void command_monitor(void* argument)
 	}
 	user_input_get(); // clean input
 
-	// set all back to input
-	for (uint8_t i = channel_start; i <= channel_stop; i++) {
+	// clean up
+	for (uint8_t i = channel_start; i <= channel_stop; i++) { // set all back to input
 		gpio_mode_setup(channel_ports[i], GPIO_MODE_INPUT, GPIO_PUPD_NONE, channel_pins[i]); // ensure pin is floating input
 	}
+	timer_disable_counter(TIM(MONITOR_TIMER)); // disable timer
+	rcc_periph_reset_pulse(RST_TIM(MONITOR_TIMER)); // reset timer state
+	rcc_periph_clock_disable(RCC_TIM(MONITOR_TIMER)); // disable clock for timer peripheral
 }
 
 /** set first channel of range to scan