Wireless doorbell question

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Tubetec

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Nov 18, 2015
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5,951
I just got a wireless door bell to use as an alerter for my avian trap ,
Receiver plugs into mains socket, 433mhz encrypted with auto pairing to the transmitter .
The transmitter is batteryless , I opened it for a look and it has an induction coil , so it seems like it pulls energy out of the air .
Does anyone know how these things work , what frequency would they use to gather the energy ?
 
Tubetec said:
The transmitter is batteryless , I opened it for a look and it has an induction coil , so it seems like it pulls energy out of the air .

I've read that they work on kinetic energy. I guess they convert the movement of/force applied on the push-button into energy.
So not "out of the air" per se. It's rather puzzling that it's enough to transmit a signal to the receiver. A crank I can grasp.
 
From the IEEE website:
"This paper presents a batteryless transmitter for wireless sensor systems. Unlike the conventional battery powered sensor transmitters, our proposed transmitter is powered from a cellular energy-harvesting circuit, a microwave energy transmission technique that has capacity to harvest 3.2 V in 5.5 hours at 0 dBm of incident cellular signals (2 GHz)...
...The cellular energy-harvesting circuit described in this work is rated 36.16 mW max, given 11.3 mA maximum transmit drain current."
Indeed, there are also wireless finger-actuated switches that convert the thumb pressure in electricity via multilayer piezo electric elements.
 
Since the typical incident radiation is likely to be in the region of -90dBm it is going to take a lot more than 5.5 hours to harvest 3.2V (whatever that means - shouldn't it be an energy quantity? Joules?).

It used to be illegal to harvest power from man made radiation in the UK.  Many years ago, a guy who lived near the Sandy Heath TV transmitter wound quite a number of turns around his loft and used it to power his lights. He was only discovered when people in his shadow claimed their TV reception was very ppor despite living close to the transmitter. He was prosecuted.

Cheers

Ian
 
ruffrecords said:
Since the typical incident radiation is likely to be in the region of -90dBm it is going to take a lot more than 5.5 hours to harvest 3.2V (whatever that means - shouldn't it be an energy quantity? Joules?).
Agreed, there are a few incoherencies in this abstract (probably drafted by an intern or a non-technical secretary).

It used to be illegal to harvest power from man made radiation in the UK.  Many years ago, a guy who lived near the Sandy Heath TV transmitter wound quite a number of turns around his loft and used it to power his lights. He was only discovered when people in his shadow claimed their TV reception was very ppor despite living close to the transmitter. He was prosecuted.
We had similar prohibitions in France; the legal basis was the state's monopoly on energy production. I don't know what's the current status after the liberalisation of domestic photovoltaic and wind installations (which are subject to government permits and contracts).
 
Thank you all for contributing ,
Im just in from  working on my trap alarm which is now operational , I was  pondering it over and it dawned on me , theres a kind of firm click to the button on the transmitter this seems to actuate a magnet which moves into contact with the coils pole pieces to produce the power .
So yeah ,its not pulling power out of the air at all  ;D
Conviction was on the right road , I steered the rest you you up the wrong track , but thanks also for digging down in to the mathmatics involved and disproving my theory .

So what I did was mount up the door bell inside a small tupperware lunch box for extra weather protection ,that gets attached to the wooden frame of the trap ,I drilled a hole through the trap frame and plastic box so a small piece of round wood can act as an actuator , I added a couple of felt pads on the transmittter button ,just for shock absorbsion . Now when the trap is triggered the button is pushed, theres also a little flex in the plastic box to help prevent damage , I used some small screws on the actuator stick  limit the amount of push the button gets and two more to prevent it from falling out while the trap is set. Another handy feature of the door bell is multiple chimes , so in theory you could have multiple traps set in a radius around your hide out position ,

I said Id post the link to the original trap vid just for clarity and context,

https://www.youtube.com/watch?v=yvKD6VkoUos

 

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