@km_hooi, your topic has been moved to a more suitable location on the forum. Installation and Troubleshooting is not for problems with (nor for advise on) your project 
See About the Installation & Troubleshooting category.
I don't have a ultrasonic sensor at hand to check if it has a crystal. But you need to provide some details.
- Please provide a link to the ultrasonic sensor that you have.
- Please provide one or more links to articles that state that "one has to touch the crystal"; I've never heard of it but that does not mean anything.
- Please provide your code.
- Please provide a clear drawing of the wiring.