Atten: Engineers/geeks whoever! Bluetooth and energy transfer.

Ok, as far as I understand it should I have a set of unamplified speakers any sound I would get out of the would be a direct product of the amount of energy my sound card gives off. Now I believe the larger the driver, the more energy it takes to produce any sound.

Ok… onto the bluetooth. How much energy does a bluetooth signal convey? Could it power the signal in a set of earbuds? (1mm driver?) If so what kind of energy drain are we looking at for the bluetooth device sending the signal? How loud could we get the earbuds to get? Or would it require an external battery on the earbud?

A battery is certainly required!

It’s true that it is possible to make a radio receiver out of only passsive components, but it requires a rather strong signal, and (unless you somehow manage to acquire enough energy to drive some fancy electronics) and a very simple modulation.

In the case of Bluetoth we have a very weak signal, and the coding requires a rather complex decoding.
The chips can be made very low-powered, but they do require power supply. It’s possible (but maybe not very probable - I’m guessing here) that it would be possible to make an earbud with solar cells on it, and large capacitors to charge up, that could work without batteries. It woud be rather large, ugly and bulky though.

It might be possible to make earphones that only receive, but in general it’s a biderectional protocol. This would then require enough battery power to output a radio signal as well, and there’s no way you can do that without batteries. Unless you have huge solar cells, or a diesel generator on your back.:slight_smile:

Way back whenever…WAY back… (15-20 years ago)

I set up a crystal radio and connected its output to a small amplifier driving a small speaker. The amplifier was air-powered - a random wire antenna (~20 feet) was connected to a bridge rectifier. The rectifier’s other input was earth-grounded. Enough voltage was available at the rectifier’s output to be usable in powering the amp - recall it was something like an LM386 chip.

The whole rig was powered by airborne radio waves. It didn’t play very loud, but it was functional.