Mitec: What Am I Doing Wrong?.

I do not really know where to post this so hope I have posted it in the right place, today I have bought one of these MiTec Micro USB to HDMI cable's/gadget and despite trying have not been able to get the display from any phone or tablet on the tv.

It has a Micro USB cable coming out of it which I presume should be connected to the phone or tablet and the other end is where the HDMI cable plugs in, at the side it has another slot which I presume is to charge your phone or tablet but having said that I have seen a demonstration of a similar device on Youtube and the device that is demonstrated needs a power cable plugged in at the side.

Surely a device would not be sold which then required you to get a power cable as an extra before you can use it would it?.

I hope there is someone who has bought this device/gadget who is able to give me some advice and look forward to your reply.

Thanks in advance.