diff --git a/lib/Ds1820.ml b/lib/Ds1820.ml
index 8ef432b..0e9c7aa 100644
--- a/lib/Ds1820.ml
+++ b/lib/Ds1820.ml
@@ -1,19 +1,45 @@
 open! Base
 
-let parse s =
-  Stdlib.Scanf.sscanf s "%s@ t=%f" (fun _ t -> t /. 1000.)
+type t = Temperature of float
+       
+let temperature f = Temperature f
 
-let%test_unit  "parse temperature" = 
-  [%test_eq: float ] (parse "brol\nmore junk text t=18241") 18.241  
+let value (Temperature f) = f
+
+let parse s =
+  let re = Str.regexp " t=\\([0-9]+\\)" in
+  try
+    if (Str.search_forward re s 0) > 0   
+    then Some (Float.of_string (Str.matched_group 1 s) /. 1000.0)
+    else None
+  with Stdlib.Not_found -> None
+
+let%test_unit "parse temperature" = 
+  [%test_eq: float option] (parse "brol\nmore junk text t=18241") (Some 18.241)  
 
 
 let read_temperature file_name =
   let open Lwt.Infix in
-  let rec aux () =
-    Lwt_io.with_file ~mode:Lwt_io.Input file_name (fun ic ->
-        Lwt_io.read_all ic >>= function
-        | None -> aux ()
-        | Some s -> Lwt.return (parse s)
+  Lwt_io.with_file ~mode:Lwt_io.Input file_name (fun ic ->
+      Lwt_io.read ic >>= (fun s ->
+        parse s |> Option.map ~f:temperature |> Lwt.return 
       )
-  in
-  aux
+    ) 
+
+let write_test_file file_name =
+  Lwt_io.with_file ~mode:Lwt_io.Output file_name (fun oc ->
+      Lwt_io.write_line oc "brol\nmore junk text t=18241"
+    )
+
+let%test "read temperature from file" = 
+  let open Lwt.Infix in
+  let file_name = "test_temperature.txt" in
+  let aux = write_test_file file_name 
+    >>= fun () -> (read_temperature file_name) 
+    >>= function 
+    | Some (Temperature t) -> Lwt.return Float.(t = 18.241)
+    | _ -> Lwt.return false
+  in Lwt_main.run aux
+
+
+
diff --git a/lib/dune b/lib/dune
index 2ab082f..092c453 100644
--- a/lib/dune
+++ b/lib/dune
@@ -1,5 +1,5 @@
 (library
  (name oblub)
  (inline_tests)
- (libraries lwt lwt.unix)
+ (libraries str lwt lwt.unix lwt_ppx)
  (preprocess (pps ppx_inline_test ppx_assert ppx_expect)))