hey, what is the cheapest way to sense radio signals coming from a mobile phone? i'd like to build a setup which let's a LED go brighter when there is strong (mobile) radio-waves in the air.
cheers, best regards Tom
I believe that cell phones emit signals when they're turned on even if they're not being used to make a call (in essence "checking in" with the cellular network).
If that's true (anyone more knowledgeable pipe up here) that's probably relevant to whatever you're trying to do - it'd mean that finding out if someone is talking on a cell phone is more complicated than just detecting signals from a cell phone.
well it's all about detecting signals. do I need an xbee and program it to a certain range of bandwidth?
xbees operate in a different frequency from cell phones. A xbee will not detect a cell phone signal. You can't change the frequency of the xbees, either.
There are LED phone charms like this one: http://cgi.ebay.com.au/Smoking-Skull-Cell-Phone-Charm-with-LED-Activity-Indica_W0QQitemZ330374408574QQcmdZViewItemQQptZPDA_Accessories?hash=item4cebd9697e#ht_500wt_975
They light up when your cellphone receives any activity, but calls generate a lot more activity than idle. They need to be close to a phone to work, but you can always use some amplification. I think they're passive. Buy one and take it apart, nothing better than a bit of reverse engineering!
Alec