GE Attenuator / Mbed 2 deprecated VAM_DAX_RELIABILITY

update hcsr04.cpp by changing 20000 to 2000

Dependencies:   Stepper mbed SDFileSystem Ultrasonic PinDetect millis

Diff: mbed.bld

Revision:
0:88834eed3de0
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mbed.bld	Sun Mar 18 02:40:25 2018 +0000
@@ -0,0 +1,1 @@
+http://mbed.org/users/mbed_official/code/mbed/builds/4336505e4b1c
\ No newline at end of file