diff --git a/firmware/apps/buggy.c b/firmware/apps/buggy.c
new file mode 100644
index 0000000..e04d436
--- /dev/null
+++ b/firmware/apps/buggy.c
@@ -0,0 +1,21 @@
+#include <stdlib.h>
+
+#include <pentabug/app.h>
+#include <pentabug/hal.h>
+#include <pentabug/photons.h>
+#include <pentabug/pentatonic.h>
+
+static void init(void) {
+	pentatonic_direction(ALL_OUT);
+	photons_init();
+}
+
+static void run(void) {
+	uint16_t light = photons_measure();
+
+	pentatonic_all_led_set(light >> 7);
+
+	wait_ms(500);
+}
+
+REGISTER(run, init, NULL);
diff --git a/firmware/include/pentabug/hal.h b/firmware/include/pentabug/hal.h
index 87f2db9..6549fc6 100644
--- a/firmware/include/pentabug/hal.h
+++ b/firmware/include/pentabug/hal.h
@@ -55,7 +55,7 @@ void buzzer_off(void);
 
 // IR
 
-// all this functions control whether a 38kHz modulated IR signal is sent
+// all these functions control whether a 38kHz modulated IR signal is sent
 void ir_on(void);
 void ir_off(void);
 void ir_inv(void);
diff --git a/firmware/include/pentabug/photons.h b/firmware/include/pentabug/photons.h
new file mode 100644
index 0000000..ff2b5cd
--- /dev/null
+++ b/firmware/include/pentabug/photons.h
@@ -0,0 +1,10 @@
+#ifndef PHOTONS_H
+#define PHOTONS_H 
+
+#include <stdint.h>
+
+void photons_init(void);
+
+uint16_t photons_measure(void);
+
+#endif /* PHOTONS_H */
diff --git a/firmware/lib/hal.c b/firmware/lib/hal.c
index f379abb..4d32d4c 100644
--- a/firmware/lib/hal.c
+++ b/firmware/lib/hal.c
@@ -113,6 +113,10 @@ void reset_hw(void) {
 	// turn ir off
 
 	ir_off();
+
+	// disable adc
+
+	ADCSRA &= ~(1 << ADEN);
 }
 
 uint8_t button_state(uint8_t btn) {
diff --git a/firmware/lib/photons.c b/firmware/lib/photons.c
new file mode 100644
index 0000000..498236c
--- /dev/null
+++ b/firmware/lib/photons.c
@@ -0,0 +1,58 @@
+#include <pentabug/photons.h>
+
+#include <avr/io.h>
+
+#include <pentabug/hal.h>
+#include <pentabug/lifecycle.h>
+
+void photons_init(void) {}
+
+uint16_t photons_measure(void) {
+	// save old state
+
+	uint8_t old_port = PORTC;
+	uint8_t old_ddr = DDRC;
+
+	// all leds off
+
+	led_off(RIGHT);
+	led_off(LEFT);
+
+	// set direction, no pullups
+
+	DDRC &= ~(1 << 3);
+	PORTC &= ~(1 << 3);
+
+	// wait for discharge
+	// TODO: needed?
+
+	wait_ms(10);
+
+	// start measurement
+
+	ADMUX  = (1 << REFS0);
+	ADCSRA = (1 << ADPS2) | (1 << ADPS1);
+	ADCSRA |= (1 << ADEN);
+
+	ADMUX = (ADMUX & ~(0x1F)) | 3;
+	ADCSRA |= (1 << ADSC);
+
+	// wait for measurement to finish
+
+	while (ADCSRA & (1 << ADSC)) test_stop_app();
+
+	uint16_t res = ADCW;
+
+	// disable adc
+
+	ADCSRA &= ~(1 << ADEN);
+
+	// restore state
+
+	PORTC = old_port;
+	DDRC = old_ddr;
+
+	// done
+
+	return res;
+}