Hello friends. I hope you can help me with my trouble. I saw many forum they say if ultrasonic sensor does not work, then try to touch the crystal. But my sensor don't have crystal......Is that a problem?
@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.
Hi, @km_hooi
Welcome to the forum.
Can you please post a link to specs/data of your ultrasonic unit?
Can you please post you code?
Please read the post at the start of any forum , entitled "How to use this Forum".
This will help with advice on how to present your code and problems.
Thanks.. Tom... 
When I typed into the search engine for this site I get 2 results. The words I used are "ultrasonic sensor touch crystal" which gets 2 results, your post and this post Ultrasonic sensor problem - Using Arduino / Sensors - Arduino Forum.
I'd guess you are using a SR04 UltraSensroThingy? Post an image of your project all wired up and not working, post the code in code tags, and explain what is meant by not working.
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