diff --git a/fw/Makefile b/fw/Makefile
index 081fb1d..084e9b2 100644
--- a/fw/Makefile
+++ b/fw/Makefile
@@ -30,7 +30,8 @@ OBJCOPY = $(AVR_PREFIX)objcopy
 #OBJDUMP = $(AVR_PREFIX)objdump
 SIZE = $(AVR_PREFIX)size
 
-OBJS = $(NAME).o dispatch.o hash.o image.o reset.o sweep.o $(COMMON_OBJS)
+OBJS = $(NAME).o accel.o dispatch.o hash.o image.o reset.o sweep.o \
+       $(COMMON_OBJS)
 BOOT_OBJS = boot.o flash.o fw.o $(COMMON_OBJS)
 COMMON_OBJS = rf.o spi.o
 
diff --git a/fw/accel.c b/fw/accel.c
new file mode 100644
index 0000000..5370260
--- /dev/null
+++ b/fw/accel.c
@@ -0,0 +1,68 @@
+/*
+ * fw/accel.c - Acceleration sensor
+ *
+ * Written 2012 by Werner Almesberger
+ * Copyright 2012 Werner Almesberger
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+
+#include <stddef.h>
+#include <stdbool.h>
+#include <stdint.h>
+
+#include <avr/io.h>
+#include <avr/interrupt.h>
+
+#include "io.h"
+#include "accel.h"
+
+
+void (*sample)(bool x, uint16_t v) = NULL;
+
+
+static bool chan_x;
+
+
+static inline void admux(bool x)
+{
+	ADMUX =
+	    1 << REFS0 |	/* Vref is AVcc */
+	    (x ? ADC_X : ADC_Y);
+}
+
+
+static inline void adcsra(bool start)
+{
+	ADCSRA =
+	    1 << ADEN |		/* enable ADC */
+	    (start ? 1 << ADSC : 0) |
+	    1 << ADIE |		/* enable ADC interrupts */
+	    7;			/* clkADC = clk/128 -> 62.5 kHz */
+}
+
+
+ISR(ADC_vect)
+{
+	uint16_t v;
+
+	v = ADC;
+	if (sample)
+		sample(chan_x, v);
+
+	chan_x = !chan_x;
+	admux(chan_x);
+	adcsra(1);
+}
+
+
+void accel_start(void)
+{
+	adcsra(0);
+	admux(1);
+	chan_x = 1;
+}
diff --git a/fw/accel.h b/fw/accel.h
new file mode 100644
index 0000000..e5c22bc
--- /dev/null
+++ b/fw/accel.h
@@ -0,0 +1,26 @@
+/*
+ * fw/accel.h - Acceleration sensor
+ *
+ * Written 2012 by Werner Almesberger
+ * Copyright 2012 Werner Almesberger
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+
+#ifndef ACCEL_H
+#define ACCEL_H
+
+#include <stdbool.h>
+#include <stdint.h>
+
+
+extern void (*sample)(bool x, uint16_t v);
+
+
+void accel_start(void);
+
+#endif /* !ACCEL_H */
diff --git a/fw/antorcha.c b/fw/antorcha.c
index c981932..0481ef9 100644
--- a/fw/antorcha.c
+++ b/fw/antorcha.c
@@ -17,6 +17,7 @@
 #include "rf.h"
 #include "dispatch.h"
 #include "sweep.h"
+#include "accel.h"
 #include "image.h"
 
 
@@ -47,6 +48,7 @@ int main(void)
 	 */
 
 	sweep_init();
+	accel_start();
 
 	while (1) {
 		got = rf_recv(buf, sizeof(buf));
diff --git a/fw/io.h b/fw/io.h
index 2ceb318..872ab25 100644
--- a/fw/io.h
+++ b/fw/io.h
@@ -34,6 +34,9 @@
 #define	LED_B7	D, 6
 #define	LED_B8	D, 7
 
+#define	ADC_X	6
+#define	ADC_Y	7
+
 #define	RF_SCLK	B, 5
 #define	RF_MISO	B, 4
 #define	RF_MOSI	B, 3