diff --git a/.gitignore b/.gitignore
index a715db0..a227983 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,3 +4,4 @@
 *.hex
 *.bin
 *.asm
+deps.mk
diff --git a/Makefile b/Makefile
index 67e23ac..fabc06f 100644
--- a/Makefile
+++ b/Makefile
@@ -16,8 +16,10 @@ default: $(PROG).hex
 clean:
 	rm -rf *.o drivers/*.o *.elf *.lst *.hex *.bin *.asm
 
-# dependencies
-blink.elf: drivers/led.o
+# automatic dependencies
+include deps.mk
+deps.mk: *.c drivers/*.c
+	for i in *.c; do echo $${i%.c}.elf: $$(./finddeps.sh "$$i"); echo; done > deps.mk
 
 # generic rules
 %.o: %.c
diff --git a/finddeps.sh b/finddeps.sh
new file mode 100755
index 0000000..7b3f986
--- /dev/null
+++ b/finddeps.sh
@@ -0,0 +1,11 @@
+#!/bin/sh
+
+search() {
+  echo "$1"
+  prefix="$(printf "%s\n" "$1"|sed 's|[^/]*$||')"
+  deps="$(grep -E '^#include "[^"]*"$' "$1"|cut '-d"' -f2|
+    \sed "s|^|$prefix|;s|\.h\$|.c|"|grep -v "$1")"
+  for i in $deps; do search $i; done
+}
+
+search "$1"|grep -v "$1"|sed 's|\.c$|.o|'