Added heartbeat to echo test

tests/echo.py

@@ -1,7 +1,8 @@
 #!/usr/bin/env python3
-
 import os
 import sys
+import time
+import _thread
 
 sys.path.append(os.path.join(os.path.dirname(os.path.realpath(__file__)), ".."))
 from panda import Panda
@@ -9,10 +10,21 @@ from panda import Panda
 # This script is intended to be used in conjunction with the echo_loopback_test.py test script from panda jungle.
 # It sends a reversed response back for every message received containing b"test".
 
+def heartbeat_thread(p):
+  while True:
+    try:
+      p.send_heartbeat()
+      time.sleep(1)
+    except:
+      break
+
 # Resend every CAN message that has been received on the same bus, but with the data reversed
 if __name__ == "__main__":
   p = Panda()
+  _thread.start_new_thread(heartbeat_thread, (p,))
   p.set_safety_mode(Panda.SAFETY_ALLOUTPUT)
+  p.set_power_save(False)
+
   while True:
     incoming = p.can_recv()
     for message in incoming: