I'm making a very small car using an ATtiny85, two 7.5v dc motors, a transistor, a servo and a bluetooth module.
My plan is to use one output pin to control both motors with the transistor, and the other to control the servo.
My main drawback is the limited range of the bluetooth. If possible, I'd like to build a simple serial tx/rx module with basic electronics. I really just need to be able to send pulses from one to the other.
As I've never gotten into radio, I have no clue what to do. Is there a simple way to do this?
Their are bands where you are allowed to use a transmitter without a license called rather unsurprisingly "license free bands" and 2.4GHz is one of them. There are others, at lower frequencies.
But while you can use these bands without a license you can not build a transmitter that uses these bands without a license. Even then the transmitter you are going to sell needs what is know as "type approval" that is you must submit you design and some samples to an approved regulatory test house to have the appropriate tests done. The with the test report you apply for a "type approval" license for that product. Paying the appropriate fee at each step.
This might cost $3000 or more depending on where in the world you are.
Well if it is not then it is illegal, simple as that.
For Europe anything for sale must have a CE mark to be legal. And while CE is self certificating the rules state for this class of circuit it must have passed the emissions approvals. I can't see any CE mark but it is permitted to be on the packaging.
Note that enforcement might be poor but it is illegal. It could be confiscated by customs on import. I did here of a knock off Arduino board from China being confiscated by the customs in Germany.
As I understand it it's admissible to put the mark on the packaging ONLY if it's not possible or feasible to mark the actual product. eek - better hide my genuine Duemilanove - no CE mark there. MEGA's ok though...
The regulators are basically helpless in the flood of devices that are now crossing borders in the huge international mail order marketplace. Not only are the numbers too large, but it's hard to enforce international transactions. How is every customs inspector supposed to know the difference? The auction sites where we buy these things have no interest in policing them. They make too much money and can claim to be an uninvolved third party.
That's how you can have punks phreaking the headset radios at the fast food outlet and getting away with it.
I believe that in the USA, part 15 allows you to legally construct and operate an AM transmitter without type approval, as long as strict criteria are met concerning the antenna dimensions and power level. I know a guy that did this, and broadcast to his small town. He claimed to have thoroughly researched all the requirements. Basically, he built the best antenna that the rules would allow.