DIY FM transmitter for wireless headphones with stuff you already have!

[airscapes]

Since I wear ear buds and I wanted to go wireless, I built an FM transmitter to attache to the MD and transmit to a walkman or any FM radio or fm headphones you may have around. I really didn't expect this to work very well as this is a very simple transmitter with no Crystal to keep the frequency from drifting. However my first 3 hour hunt was perfect with clear sound and no static during times with no signal. The frequency was rock solid till the end of the day when I need to change the channel by one click.

This is a neat project if you enjoy DIY electronics and if you do enjoy this hobby you should have most if not all the parts in your junk box. I spent about $8 for the board and 1/4 stereo plug. Everything else I had or pulled off of old boards (old dead electronics) The only thing I did have to do was attenuate the output of the MD with 1.2M ohm of resistance as the Coinmaster GT does not have a volume control.

Here is the site with the instructions on the basic transmitter.
http://makezine.com/projects/super-simple-fm-transmitter/
Sucrets box is held on with some Velcro.

 

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[airscapes]

I upgraded this transmitter with a variable capacitor as is suggested in the instructions. I did not have one and wanted to make sure this would work as well as I had hoped before ordering a few.. can't get them at radio shack so I order 5 since shipping was more than the parts.. After installing it I was able to get the output fine tuned and it can be adjusted very quickly if I should happen to be someplace where there is a commercial station on that frequency. Without the var cap it is a real pain to adjust the frequency by stretching or compressing the coil winding. I see a lot of talk about wireless head phones in the hundreds of $$. If you have the skill set go for this, it really is very good and not very expensive.

 

[airscapes]

Added a 7" piece of wire for an antenna and can now set my walkman to "local" reducing the interference of strong adjacent station. Very happy with how well this works!

 

[airscapes]

I have attempted to build another transmitter to use with a smart phone. I have found that this simple transmitter does not work very well for that purpose. There is probably a way to fix this but I am not an electrical engineer.
The problem is with a smart phone the output level is very low compared to a MD with no volume control. The phone/ipod is at or below reference line level and the MD is at 1 or more watts. With the low level input there is no resistance in the input side and the input wire changes the capacitance of the transmission side of the circuit. This makes it very unstable, where just moving the input wire or device caused frequency shift.

With the added in-line resistors 1M in the 1/4" plug and another 100 ohms where the input wire attaches to the board this change in capacitance is eliminated. That make is work really freaking great with a MD but you can not use it with a low level input device..

Doesn't look like we have any other electronics tinkers here but this may come up on google searches for those who are interested in this but not Metal Detecting.

 

[Doc Arey]

Very Cool!

 

[Higgy]

I'm thinking you got what it takes to make a decent amount of cash if you can actually design, test, and manufacture a decent plug-and-play wireless module. I'd buy one.