Wrong url

Hello,



I have made an addon by myself wich almost works well



When i place on my product page an url which has to point to an external website i got a problem:



I places this code in my scripts:






Where $external_url must show the url
www.test.nl which point to the external website.



But when i click on the url in the front of my site i get an error page because my website url is also placed in front of the external url like this:



mywebsite.nl/www.test.nl



Does anybody know how i can solve this?



Thanks