IR wireless headphone project.

[dfbowers]

I have not tried this yet with metal detectors, but seems that it might be practical.
Maybe a winter project?

Don

[Sean_Goddard]

As long as no one else has a pair that same, or it's not a bright sunny day (not much chance on that in the UK though) and you can keep the sensors pointing at each other. I'd give up on IR before I started. Good luck though.

Maybe you'd be better off trying a simple FM transmitter/ receiver combo at some obscure frequency. Keep the ERP down or you might find yourself in trouble with the FCC. best look at a blue-tooth module (cable replacement).

[Skippy]

I think IR will be unreliable. I'm working on an RF system at the moment, but that's also hard, the power level needs to be tiny (a few 100 microwatts maximum) to avoid interfering with the detector. Placing the transmitter on the elbow cup, so it is further from the control-box seems one obvious thing to do. Bluetooth setups dont work well, there is a huge time delay with them, apparently, making detecting difficult.

[A Gumby]

http://www.walmart.com/ip/Scosche-FM...itter/14666784

$12 in the automotive audio section of my Wal-Mart.

Tune it to an unused part of the FM band (it's digitally synthesized, so it doesn't drift), then listen on an MP3 player with FM or a cheap FM "Walkman." This works great as a wireless headphone for TV viewing without disturbing others. The transmitter has a range much greater than the 10 feet claimed in the manual (I can walk around the entire house and still hear the TV audio just fine) and the battery life is much greater than the claimed 15 hours on two AAAs.

You might be able to open it up and sever the antenna trace or lead to reduce radiated power.

[Sean_Goddard]

Get your hands on a set of CREATIVE Technology BT headphones. SOMEHOW they got rid of the delay. I pulled a set of their cheap ones apart and put the the Tx in a separate box mounted on the arm rest. The Rx is hip mounted and adapted so I can plug ANY make or type of headphones in I want.

I've tested it and the delay is around 50mS. fast enough for a beeper.

BTW, I wouldn't worry too much about the RF, the frequencies of RF and beepers are VASTLY different and if the machine you are using is anything other than a $5 crock of crud, anything up to around 200mW should be OK (just make sure you steer clear of beeper Tx harmonics though). Good luck and if I can help in any way, I'll do my best.

[DavidB]

I always wanted to experiment with an ultrasonic oscillator being phase modulated by the detectors audio tone and driving a transducer. At the receive end, a simple transducer, amplified, filtered and demodulated with a PLL to get the original detector audio then the typical headphone amp stage. I would think that at such a short range it would work ok and keep the dogs away at the same time.

[A Gumby]

BTW, I wouldn't worry too much about the RF, the frequencies of RF and beepers are VASTLY different and if the machine you are using is anything other than a $5 crock of crud, anything up to around 200mW should be OK (just make sure you steer clear of beeper Tx harmonics though). Good luck and if I can help in any way, I'll do my best.

The meter on my Bounty Hunter Tracker IV (which may very well be in your "crock of crud" category), pegs for an instant when I first turn on the FM transmitter I mentioned. Of course, the detector's electronics are in a plastic case. Not surprizingly, the xmt power of the FM xmtr isn't specified anywhere in the user manual. I haven't done any detector de-sense tests and don't intend to until I cut the antenna trace/lead to reduce power output.

[Aziz]

http://www.walmart.com/ip/Scosche-FM...itter/14666784

$12 in the automotive audio section of my Wal-Mart.

Tune it to an unused part of the FM band (it's digitally synthesized, so it doesn't drift), then listen on an MP3 player with FM or a cheap FM "Walkman." This works great as a wireless headphone for TV viewing without disturbing others. The transmitter has a range much greater than the 10 feet claimed in the manual (I can walk around the entire house and still hear the TV audio just fine) and the battery life is much greater than the claimed 15 hours on two AAAs.

You might be able to open it up and sever the antenna trace or lead to reduce radiated power.

Hi Gumby,

this device very likely utilizes the BH1417 chip. One can mod it to achieve a much longer distance . According to the data sheet, it can utilize up to 20 mW (that's really huge RF power). I think, it is very likely reduced heavily (<50µW).

Who the **** has limitted the max. RF power to 50 nW in EU? Must be some brain ****** people.
We in EU are only allowed to transmit 50nW (nano Watt). As a result, we see devices, which doesn't work properly (you have to put it very close to the receiver).

Aziz

[Sean_Goddard]

I like DavidB's idea, that sounds "sound" if you pardon the pun. A Gumby, your machine (or ANY machine for that matter) will probably peg for an instant whilst the oscillator in the FM settles. When you first turn on, it will "broadband" until it reaches "steady" state and the frequency determining components start to do their job..

Aziz, yes in some terms 20mW is a quite a bit, in deed it will give you about a mile range on the TX with a good RX! I'm a little more used to powers up to a few KW, but that's a bit too much for this task (imagine the size of the battery pack)