DIY Audio Projects Forum
http://diyaudioprojects.com/Forum/

Quality of simple DIY FM transmitter/receivers?
http://diyaudioprojects.com/Forum/viewtopic.php?f=16&t=5719
Page 1 of 1

Author:  SlamBamActionman [ 07 Nov 2016, 15:18 ]
Post subject:  Quality of simple DIY FM transmitter/receivers?

Hello! First time poster and this project might only be tangentically relevant to this forum, but I feel that if I'm gonna ask someone about this I might as well ask the experts:

I originally have cosplaying (dressing up as comic- and videogame characters) as a hobby and recently I've been planning a fun project involving two people, where one has a "talking" object and the other person is the one providing the voice to that object. The way I imagine doing this would be to put a speaker in the object (in this case a sword) and a mic on the person providing the voice. However it'd look really silly to have a wire going between the weilder of the sword and the person doing the talking, so I hope to solve this using wireless transmission.

Theater mics are expensive as heck and bluetooth devices only seem to have a range of about 10 feet, which won't do. Eventually I stumbled upon DIY FM radios and they seem like the solution since they are both small and relatively cheap. I was thinking of building something like this ( https://youtu.be/joFourugXvs ) but what worries me is the quality of the broadcast. It's been difficult finding any good videos where a homemade transmitter is used together with a homemade receiver so I can't tell if the sound quality will end up being too distorted or grainy for this to be a worthwhile project.

Any of you who can offer helpful advice/experience on this? Is the loudspeaker the determining factor or will the signal itself be too crappy to do anything about?

(And yes, I am aware that I am a newbie in this field. I'm grateful for any help I may get. :p)

Author:  Peter W. [ 08 Nov 2016, 16:31 ]
Post subject:  Re: Quality of simple DIY FM transmitter/receivers?

[quote="SlamBamActionman"]

Any of you who can offer helpful advice/experience on this? Is the loudspeaker the determining factor or will the signal itself be too crappy to do anything about?

Here are the issues in a nutshell:

a) What you have presented is a specific solution to a specific issue. There are inexpensive microphones available in the US$3- $10 range that will do just fine at voice frequencies. https://images-na.ssl-images-amazon.com ... L1200_.jpg is one of them - Amazon.

b) if you build the tiny transmitter you have in mind and add a jack instead of a crystal microphone as show, you have the ability reduce flanking noise when you transmit. And, if you really do want to go 'high-end' and spend US$40 or so, you could go with a throat microphone.

c) One issue not addressed in the video is how to adjust the transmitting frequency overall - that is done by spreading the windings on the coil a bit, or compressing them a bit. It is unlikely that the trimmer will cover the entire 87.9 - 108 range without additional adjustments to the coil - just an FYI. Radio Locator will give you open frequencies in your area so you do not violate Part 15 regulations - and, for the record, DO take them seriously!

d) Which leads to the 'delicacy' issue. You will want to put the transmitter into some sort of project box so that the coil does not get bumped, crushed or damaged in use. Any such impact will change the transmitting frequency instantly.

Now, apart from all that - if all this is for is the purpose you describe, it will be fully adequate towards making a credible "Talking Sword". As the unit will transmit in mono, to, very likely, a mono tuner/receiver, there will be no carrier issues and as only voice frequencies are contemplated, even a very narrow spectrum will be fine. And I would suggest you not spend another nickel than you must. The worst that could happen is that you learn something about how these beasts work.

On the other hand, if you want to have a more useful transmitter, one that covers a much greater range with complete reliability and perhaps in stereo, you will have to spend much more serious money for something that is both reliable and well made. I restore old radios and vintage audio equipment, so I keep a "proper" (for my needs) FM stereo transmitter that covers my house and allows me to annoy the neighbors - should they choose to be annoyed - and still remain fully Part-15 compliant. But that unit did cost me well over US$200 as a *kit*.


Good luck with it!

Author:  SlamBamActionman [ 08 Nov 2016, 17:16 ]
Post subject:  Re: Quality of simple DIY FM transmitter/receivers?

Peter W. wrote:

Here are the issues in a nutshell:

a) What you have presented is a specific solution to a specific issue. There are inexpensive microphones available in the US$3- $10 range that will do just fine at voice frequencies. https://images-na.ssl-images-amazon.com ... L1200_.jpg is one of them - Amazon.

b) if you build the tiny transmitter you have in mind and add a jack instead of a crystal microphone as show, you have the ability reduce flanking noise when you transmit. And, if you really do want to go 'high-end' and spend US$40 or so, you could go with a throat microphone.

c) One issue not addressed in the video is how to adjust the transmitting frequency overall - that is done by spreading the windings on the coil a bit, or compressing them a bit. It is unlikely that the trimmer will cover the entire 87.9 - 108 range without additional adjustments to the coil - just an FYI. Radio Locator will give you open frequencies in your area so you do not violate Part 15 regulations - and, for the record, DO take them seriously!

d) Which leads to the 'delicacy' issue. You will want to put the transmitter into some sort of project box so that the coil does not get bumped, crushed or damaged in use. Any such impact will change the transmitting frequency instantly.

Now, apart from all that - if all this is for is the purpose you describe, it will be fully adequate towards making a credible "Talking Sword". As the unit will transmit in mono, to, very likely, a mono tuner/receiver, there will be no carrier issues and as only voice frequencies are contemplated, even a very narrow spectrum will be fine. And I would suggest you not spend another nickel than you must. The worst that could happen is that you learn something about how these beasts work.

On the other hand, if you want to have a more useful transmitter, one that covers a much greater range with complete reliability and perhaps in stereo, you will have to spend much more serious money for something that is both reliable and well made. I restore old radios and vintage audio equipment, so I keep a "proper" (for my needs) FM stereo transmitter that covers my house and allows me to annoy the neighbors - should they choose to be annoyed - and still remain fully Part-15 compliant. But that unit did cost me well over US$200 as a *kit*.


Good luck with it!


Thanks a lot for such a thorough reply! I will definitively look into what coil and spread to use and while the receiver would be safe inside the sword I'll take an extra look at how to protect the transmitter as well. Since I live in Sweden I'll have to look at what laws apply here but that shouldn't be much of a problem.

I'm very excited to see this project through and glad that it's not an impossibility! Thanks again for sharing your knowledge!

Author:  gofar99 [ 09 Nov 2016, 11:34 ]
Post subject:  Re: Quality of simple DIY FM transmitter/receivers?

Hi, It would probably work OK. The issue as you suspected it the speaker. The frequency response of the transmitter is usually quite good and would be suitable. The receiver is up for grabs. Some are good some not. The speaker though will probably have the greates effect. Smaller ones usually are quite "tinny" and bigger ones would not likely fit in your project. A fun thing to try...but uncertain if it will do as much as you want.

Good listening
Bruce

Author:  SlamBamActionman [ 09 Nov 2016, 17:43 ]
Post subject:  Re: Quality of simple DIY FM transmitter/receivers?

Hi Gofar. Luckily the sword happens to be very big and with a suspiciously fitting round part in the middle. The only thing I will have to worry about is the loudspeaker's thickness, as long as I manage to store the receiver itself in the triangle-shaped part. https://www.supergiantgames.com/webhook ... 013_01.jpg

While I am satisfied with the answers I've gotten so far, I have a side question that isn't necessary for the project to be completed and might be trickier to answer, but if any of you have pointers to where I can look for more information about it I'd be delighted. To simplify, would it be possible to have a diode (or in this case several) light up when sound is being played through the speaker? I know it's not as simple as having a regular electrical current when it comes to audio and thus might be harder to detect.

Author:  Peter W. [ 10 Nov 2016, 07:46 ]
Post subject:  Re: Quality of simple DIY FM transmitter/receivers?

SlamBamActionman wrote:
Hi Gofar. Luckily the sword happens to be very big and with a suspiciously fitting round part in the middle. The only thing I will have to worry about is the loudspeaker's thickness, as long as I manage to store the receiver itself in the triangle-shaped part. https://www.supergiantgames.com/webhook ... 013_01.jpg

While I am satisfied with the answers I've gotten so far, I have a side question that isn't necessary for the project to be completed and might be trickier to answer, but if any of you have pointers to where I can look for more information about it I'd be delighted. To simplify, would it be possible to have a diode (or in this case several) light up when sound is being played through the speaker? I know it's not as simple as having a regular electrical current when it comes to audio and thus might be harder to detect.


http://d2ydh70d4b5xgv.cloudfront.net/im ... 8214bd.jpg

Do a search on "Flat Oval" speakers and you may be able to get a lot more sound than you might think in a narrow package. What is linked above is only one of many.

https://www.vellemanstore.com/en/vellem ... oCoSTw_wcB

Not very expensive and all you need in one little package. Again, protect it inside some sort of enclosure, but this device is not much larger than the 9V battery that drives it.

Author:  SlamBamActionman [ 10 Nov 2016, 18:36 ]
Post subject:  Re: Quality of simple DIY FM transmitter/receivers?

Peter W. wrote:
http://d2ydh70d4b5xgv.cloudfront.net/im ... 8214bd.jpg

Do a search on "Flat Oval" speakers and you may be able to get a lot more sound than you might think in a narrow package. What is linked above is only one of many.

https://www.vellemanstore.com/en/vellem ... oCoSTw_wcB

Not very expensive and all you need in one little package. Again, protect it inside some sort of enclosure, but this device is not much larger than the 9V battery that drives it.


Thanks for the links. Unfortunately Velleman does not ship the kit to Sweden, however, I found the manual for it and it lists all the components. After googling around some I found a cheap Swedish site which stocks the same Velleman components. I'll have to do without the board that comes with the kit but it shouldn't be impossible.

While having a seperate mic that detects the sound that the receiver is emitting isn't ideal I will take it. I'll be looking into if it'd be possible to hook it up to the same circuit that the receiver runs on and if it doesn't work then no harm no foul.

You've all been really helpful and I'm grateful for that. :) Thanks a bunch.

Author:  Peter W. [ 11 Nov 2016, 07:43 ]
Post subject:  Re: Quality of simple DIY FM transmitter/receivers?

It should be entirely possible to run the speaker output into the light board directly via a fairly large (high-resistance) resistor. This would not reduce the volume on the speaker significantly either.

Another idea that just came to mind is a conventional walkie-talkie. And some of those have an LED that lights when receiving. Probably will cost you more than what you contemplate, however, for something reliable and with sufficient range under difficult conditions. And I am not sure how Sweden treats these things. In the US, they are almost toys.

http://wwww.factoryoutletstore.com/cat/ ... adios.html

However, it is always more satisfying to cobble your own solution than to buy it right off the shelf.

Page 1 of 1 All times are UTC - 6 hours [ DST ]
Powered by phpBB® Forum Software © phpBB Group
http://www.phpbb.com/