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How do they do that cordless headphones for a metal detector

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iannotts

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Hi
I`m very new to the forum in fact just under the hour new and i`ve had a really good search for an aswer, but i can`t seem to find one.

So please help if you can.

What I would like to do is make wireless headphones for my metal detector.

Simple eh?? Well i thought so. I`ve looked at a simple fm transmitter to a pair of headphones that have a radio in them you know the sort the ones with the ariel to pull out. I`ve looked into IR but line of sight is a problem. I`ve looked at vox operated walkie talkie set up.

All i want is a single fixed frequency set up to plug in to the jack plug on the detector and the head phones to pick up the signal.

Bluetooth headphones some how just don`t work.

It does not even have to be stereo, mono would be fine. Transmit range need only be 5 or 6 feet. If anyone has any ideas it would be greatly welcomed.

Thanks

Ian
 
How about hacking an old toy Walkie-Talkie?
 
Must say that looks like the perfect solution the transmitter and radio.

Just one question.

Would it be possible to replace the mic on the transmitter for a jack plug for audio input. How might the transmitter need be modified to enable this.

Ok two questions really i lied......:)
 
Remove the micropohone and replace it with a jack in series with a 1M resistor to act as an attenuator.
 
iannotts said:
Must say that looks like the perfect solution the transmitter and radio.

Just one question.

Would it be possible to replace the mic on the transmitter for a jack plug for audio input. How might the transmitter need be modified to enable this.

Ok two questions really i lied......:)

Yes, you can replace the mic with a jack plug, but the microphone generates a lower voltage than your equipment, so you will have to reduce your input voltage if you connect in place of the mic. This is probably easiest to do by putting a potentiometer between your new input and the point where the microphone was connected. You must also include a series capacitor to block any DC voltages. I recommend a 1 Kohm potentiometer, although a 10K or 5K would probably be OK too. The series capacitor is needed on the output side of the potentiometer and you may also need one on the input side so that you aren't pulling DC current from your equipment. Without knowing the circuit of these items putting one on each side of the pot is safest. You should use capacitors of 4.7 uF or a bit larger and put the - side of each capacitor towards the pot.

When adjusting for level, start with the pot rotated for lowest level. Turn on the wireless mic and then tune the FM receiver into that signal. You should hear a quiet spot on the FM dial, as if you are hearing a strong station with no one talking. Test that it is your signal by turning your transmitter on and off. One of the normal things that you have to fuss with is that you have to find a quiet spot on your FM band away from other stations so that you don't get interference. It should be possible to tune the frequency of your transmitter using a variable capacitor. Your transmitter kit should have instructions telling you which part to rotate for this. Once you have a spot picked out and your transmitter sending a carrier, you feed some audio from your other equipment and slowly turn up the potentiometer for adequate sound level. This is FM, so if you turn the sound up too much, you get distortion and lots of it. So if it sounds awful, back off the level and try re-tuning your FM receiver for clearest audio.
 
I had a closer look at that one example FM transmitter and perhaps that isn't the best one if you are going to buy. The same vendor has another model with a line input:

**broken link removed**

With this one, you don't have to add anything.

And I note that these are tuned by varying the inductor slug instead of with a variable capacitor. This has the same effect, but is a bit harder to do because most screwdrivers don't fit real well and you might have to whittle a small tool from a piece of hardwood for best fit.
 
Many thanks RadioRon for all the time and effort you have put in to sorting out a solution for me.

I`m really glad i`ve found this place. What a fountain of knowledge. I only hope i can add my thoughts someday.

Thanks


Ian
 
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