Ultra µ-Power FM Receiver Circuit

Discussion in 'Wireless & RF Design' started by fabxy1, Oct 3, 2014.

  1. fabxy1

    Thread Starter New Member

    Oct 3, 2014
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    Dear Community,

    I need your help - for a extended school project (Topic: Effective transmission of sound) I'll have to build up a fully-functional wireless audio receiver.
    How I realize it (digital/analog) is doesn't matter - but the "big thing" is, that it needs to be as small as possible because the hole project should be realized as a pair of wireless in-ear buds.
    Because of the limited battery size (~1/4AAA or button cell) and therefore the limited capacitance, the circuit should work - if possible - with:
    • Supply Voltage = 1.2V
    • Current ~ 0 - 10mA (if somehow possible)
    • And of course: as small realizable as possible!
    At the moment I'm not really sure, if it's better to do the transmission digitally or analog - as far as I know, it's maybe more current-saving doing it all analog (µ-Power FM receiver?)?
    But because I'm not sure - I'm asking YOU!
    I'll appreciate every advice and suggestion of yours. Of course - circuits (or snipets of) are more than welcome :)
    Thank You in advance.

    Greetings from Germany,
    FabXy1

    In attachment (some examples how the hole thing could might look like):
    http://www.ansem.com/appstories/9999/8/ultra-low-power-fm-receiver-for-hearing-aid
    microearpiece.jpg EPSN2297.JPG post-46-1131983272.jpg Invisity2.jpg Invisity1.jpg phonitodigital.jpg
     
  2. alfacliff

    Well-Known Member

    Dec 13, 2013
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    how far are you planning on the thing recieving? a crystal detector with tuned circuit wold be smallest and use no power, but would not be very sensative. also would only work on am.
     
  3. fabxy1

    Thread Starter New Member

    Oct 3, 2014
    11
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    Thank you for your reply, alfacliff.
    On planning how the thing should receive I'm open for all suggestions - I also thought about a crystal detector but my probleme is - as you mentioned - the sensitivity and failureproneness. I'm not quite sure, how I could stabilize the AM-transmission on a "FM-level". The geographical distance, the signal needs to be transmitted is at about max. 10m.

    If I only have the choice of AM, have you an idea how I could maximize the quality to its limits?
     
  4. BR-549

    Well-Known Member

    Sep 22, 2013
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    fabxy1, a few questions for clarity.

    1. What is the audio bandwidth required? Would being able to talk thru a phone line suffice{3000 hz)? Or do you need the bandwidth of a hearing aid? I spent some time on the hearing aid link.....but could not find any technical info. I’m going to guess a hearing aid bandwidth of 10 khz. Or do you need FM stereo(many,many khz)?
    2. I am confused about the hearing aid link. You say you want a ear bud device. Do you consider that hearing aid an ear bud device? Or is the link to show what functionally you want? Again...there is no data sheet on link.
    3. I’m assuming 10m means 10 meters.
    4. What is your budget?
    5. How many units?

    It’s hard to advise when not knowing exactly what you are trying to do.
    Are you a watchmaker? If not......it will have to be built for you.
    Depending on what you need, it will probably take a custom chip. And that’s not as hard as you might think. In 2001 I had several chips made for a similar app for military.....but it was cigarette size. I hope I’m not wrong, but it should be easier to do now.
     
  5. alfacliff

    Well-Known Member

    Dec 13, 2013
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    not hearing aids, in the ear recievers.
     
  6. BR-549

    Well-Known Member

    Sep 22, 2013
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    Ok, what does he want to RX? What is the source? Perhaps someone makes a bluetooth ear bud?
     
  7. BR-549

    Well-Known Member

    Sep 22, 2013
    2,007
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  8. BR-549

    Well-Known Member

    Sep 22, 2013
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  9. fabxy1

    Thread Starter New Member

    Oct 3, 2014
    11
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    Thank you BR-549 and alfacliff for your replies.
    To clear your questions:
    • the device requires a audio bandwith for .. lets say mono fm (~20-16/20kHz)
    • I'd like to independent devices/earbuds without a cable which is connecting both together
    • Don't be confused - the hearing aid link just should show you, how I have in mind to "realize" the circuit board design. It pretty much reflects my thoughts of the future design of the device (just the circuit board!). Also I've choosen this link because the device pretty much has the same voltage/current characteristics like I would want to have them for my device. So for a better understanding - the link should just show the wished functionality. I don't want to build up a hearing aid fm receiver, but something that is able to deliver audio/music in a similar way.
    • That's correct, I meant "meters" - a range of about 10 meter would be quite perfect. Power consumption on the transmitter side doesn't play such a big role as the consumption on the receiver side. But range isn't everything at first - a range of about 2-3m would also be quite good.
    • Because it's a school project, my budget isn't that "great" - but because of my also private interest in the hole project, I would probably say, that the budget is quite "open".
    • If the project/circuit works fine, it could be, that I need to produce some more - maybe at a later point I could even sell some of these. So let's say now .. maybe 50 units max. (at the moment)
    • I'm a watchmaker or more precisely - I love to make sth. by my self - so I would prefer to produce/craft the circuit by myself for now.
    • Oh that sounds great if I later wanted to sell these things - but at the moment it would be quite better to do it on a breadboard/pcb?!:-o But I would appreciate it very much to get some more information about the "DIY chip engineering":)
    My source would be the audio jack output from a computer or mp3 player.
    The intention of the hole thing is to make it possible hearing a song playing on the used mp3 player on the wireless earpieces.
    I think a bluetooth solution is not quite suitable because of it's high power consumption (>30mA; 3.3V min).
    Options for a solution would because of that might be:
    - FM
    - AM
    - Self-developed digital audio transmission (Analog audio jack signal is converted by a ADC to a digital signal which then is transmitted by AM/FM, digital signal is received by AM/FM low power receiver (earbud), then converted back analog, amplified and then goes on to the loudspeaker.

    A light-block diagram is attached to this post:)
    After midnight greetings from Germany,

    Fabian (FabXy1)
    Example.jpg
     
  10. BR-549

    Well-Known Member

    Sep 22, 2013
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    Real fine Fabian, thank you.

    Here’s what I recommend. Here in the states and think in Germany.....they have certain bands of frequencies that allow low level, unlicensed transmission. There is one around 462-463 Mhz. The reason I recommend starting here is because many Asian companies sell little transmitter and receiver boards real cheap. Look for AM boards. You will need to mount and power the TX board at the computer. The board will be modulated by the line out connection.
    Now remember......this is just proof of concept recommendation. Your final result will probably be at a high frequency because you will want a smaller antenna, but bare with me for a minute.

    For the proto-type receiver circuit, I would try alfacliffs’ advice. The receiver board that comes with the transmitter board, will probably have an oscillator/ detector stage and an isolation or buffer amp stage. Pull these transistors out and install a diode detector, it doesn’t need power. Using the tuned circuits on the board.......your diode detector should easily pick up the signal. You should be able to here signal in head phones from the detector. Now pick up your proto RX board and see how far away you can here RX signal. You might be surprised and not need batteries in your RX. This is well worth checking out.

    If this works, there are other cheap frequency boards(800-900 Mhz and a little above 1-2 Ghz) that can be used as your final project.........but you will probably need your watchmaker skills to modify the RX.

    For the range you want and the power that you are concerned with, this might be your best solution. Especially for a school project. It shows how old technology can work with the new.

    I think alfacliff has a great idea. And of course after me promoting it.........if it doesn’t work........we can still blame him. I love this forum. nyuk, nyuk.

    ok back to Germany.
     
  11. skeptic

    Active Member

    Mar 7, 2010
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    Last edited: Oct 5, 2014
    BR-549 likes this.
  12. fabxy1

    Thread Starter New Member

    Oct 3, 2014
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    Thank you BR-549 and also skeptic :)

    I still have some questions and I'm a little bit confused about your nearly "to perfect to be so"-solution, BR-549.
    My problem is, that I think, that the transmitter would never emit as much power as the receiver would require to deliver a stabilized sound quality without any kind of power source (=> crystal detector/radio).
    Are you really sure, it could work out without beeing to insensitive and even more important, not to distorted? - Because sound quality does also play a quite big role .. on some of the ISM frequency channels the maximum allowed EMR-power output is about 25-50mW.
    So if you could say or kind of "guarantee" me, that the whole technique could workout, I would give it a try and order all the stuff.

    My next question is about distortion => could I use any filters or something like that to filter out distortion caused by interference or is it only possible if we would use FM?
    Third question - wouldn't it be a good idea to send out not only 2 channels for L/R Audio .. but lets say, 2 additional channels just for power purposes?
    Couldn't I operate some kind of "energy harvesting" and use the electromagnetic waves to power up maybe a FM slope detection stage with some additional filters to have a quite undistorted signal aswell as a "loud" sound on 8 - 32 Ohm Speakers? - because then, only the transmitter would consume power and the receiver is even smaller and lighter?! - help me:eek:!

    If you can find any example circuits, I would appreciate, if you could send them over, ok?:)
    I hope, I can find a solution that meets my wishes!

    Of course - best thing still would be to get away maybe from "AM" and switch over to "FM" because of the distortion risk (and as far as I know, the strongest FM signal next to the receiver mostly outweighs and therefore is demodulated quite clearly?
    I hope you understand, what I'm thinking :)

    PS: If we could maybe find a solution for a AGC? - that would be perfect!

    Good night from Germany!
    - Fabian
    Example_Power_Transmission.JPG <= Concept of Power Transmission? - Give me your comments :)
     
  13. BR-549

    Well-Known Member

    Sep 22, 2013
    2,007
    395
    Ok Fabian. Sorry, I didn’t know a guarantee was requested. If a guarantee is required, it can be granted along with the appropriate fee and under certain conditions.

    It will cost you less than $10 to see if detector will work. That is your decision. But I wouldn’t want you to waste your time. From the way that you ask questions and change your requirements...........maybe a little more study is warranted. For you.

    In closing.....I still recommend to you, those bluetooth earbuds, those along with a $2 dongle will give ALL you want.

    Good Luck.
     
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