wireless microphone problem

[sputnik]

Hey guys I'm trying to design a simple and small wireless mic that allows tranmission over bluetooth or wifi (only needs to transmit over very short distances - under 5meters is fine)

It needs to be very very simple, as in I don't mind if all it does it continuously transmit data without a switch.

It also needs to be very small (if the board can be no larger then 2cm on a side that would be perfect (I'm using a 3mm x 6mm microphone)

This is for a medically related research project, however I have absolutely no experience in electronics and am currently stuck in the design phase, Any help would be greatly appreciated.

 

[CocaCola]

Go to Ebay and type in 'Spy Bug'

You can get a small self contained device for cheap plug in an standard cell phone SIM card, and when you call it you have wireless microphone

There are also several other ones that can be found in Ebay and Google searches, scroll the pages, some real small ones that plug right onto the top of a 9volt battery and transmit to a nearby radio, they can be had for under $10 and some larger ones that likely perform a little better for a few bucks more...

Do your own search these are just random Ebay hits, no recommendation or endorsement just some I grabbed from a search jumping around a few pages!

http://www.ebay.com/itm/Spy-Quardba...730?pt=LH_DefaultDomain_0&hash=item3cc73a1af2

http://www.ebay.com/itm/Mini-Fm-Spy...t=US_Surveillance_Gadgets&hash=item27c7c3e731

http://www.ebay.com/itm/FM-SPY-BUG-...t=US_Surveillance_Gadgets&hash=item3cc6d1d78d

 

[sputnik]

Thanks CocaCola, I'll check these out. Maybe FM tranmission is the way to go...

 

[donkey]

you can find other recording equipment if you look for it, but seriously the FM band has the great bonus of not being OVER used. wi fi works on 2.4ghz or 5.8ghz and alot of devices are now using these bands so interference is an issue, being a medical device I am guessing that is something you will want to avoid. blue tooth also is in the 2.4ghz range.

alot of FM bugs will broadcast to any fm station so you can easily pick one thats not in use or you can get others that have a specific frequency.

have to ask, is this like a wireless stethoscope or something?

 

[CocaCola]

wi fi works on 2.4ghz or 5.8ghz and alot of devices are now using these bands so interference is an issue

I'm having a hard enough time balancing that interference within my own household right now, it's really annoying that there is so little free bandwidth available to the pubic for wireless devices...

Like Donkey said there is a lot more dead space on the FM or even AM band...

 

[sputnik]

After some thought I agree the FM would be best for a prototype stage but I believe I will ultimately need bluetooth, or something similar that can transfer data and run simple programming with a bluetooth stack.

I've done some google searching but I've come up short. Would anyone know where to find a site where simple schematics for bluetooth transmitters could be found?

In the mean time I will start with the FM idea, many thanks to those who suggested it

Also, Donkey, it's somewhat like a wireless stethoscope, but ultimately needs to have some ability for data transfer along with sound so that it can be left to record without anyone there.

 

[CocaCola]

Google 'bluetooth module' or hit up Ebay and search for them they are cheap or at least reasonable, the modules circuit is likely right out of the chipsets datasheet for a working model...

 

[donkey]

blue tooth is a great idea for this project then as bluetooth transmits data. there is very little existing, if anything, that transmits data over FM
a quick review seems the limit of bluetooth v1.2 was a speed of 721kbps. that is a hell of alot faster than i realised and should stream nicely.
the only issue I have with bluetooth is making it safe, you would hate some moron trying to pair with your device while you want to hear a heartbeat. setting it up safely would mean pairing the device in the workshop/lab first and then locking out all other signals. the only problem with that however is that if one end breaks you can't just swap that end you have to get the new unit paired to the old.

 

[CocaCola]

After some thought I agree the FM would be best for a prototype stage but I believe I will ultimately need bluetooth, or something similar that can transfer data and run simple programming with a bluetooth stack.

I'm not against Bluetooth in the least it offers many advantages, but just wanted to touch on the topic that you can send data over FM... It all depends on how much and how fast you want or need to send the data... And not to roll back to days gone by but something as simple as Morse code can be sent over FM very easily and pretty reliably, checksums can be included to verify the data... There are also other issues, like privacy and the sorts using open FM channels so it might not fit the bill in other regards... More so I just wanted to point out that FM can still be used for data in some cases...

the only issue I have with bluetooth is making it safe, you would hate some moron trying to pair with your device while you want to hear a heartbeat. setting it up safely would mean pairing the device in the workshop/lab first and then locking out all other signals. the only problem with that however is that if one end breaks you can't just swap that end you have to get the new unit paired to the old.

They could still be paired during manufacture and include a user option to pair them again at a later date, possibly one of those little pin hole buttons that are used for resets all the time or an internal pairing switch inside the units or even a specific keypad or button combination to set it in pairing mode...

 

[sputnik]

The pairing thing is a bit of an issue as it would be ideal to simply pair it with an iPhone (and have an app on it that could translate the data). The more I look into bluetooth the more daunting it appears, both in monetary terms and complexity. For someone with no electrical engineering knowledge trying to understand where to place resistors, etc without copying a previous schematic might as well be impossible. So I'm very limited to what I can find as far as schematics go on the internet.

Also although a pre-made bluetooth circuit can be bought, I'd ideally like to make my own from scratch using a bought bluetooth chip. This would save a lot of money, especially if everything is successful and I wish to make multiple copies. Not to mention is feels better to make it all yourself haha.

If I were to just use FM I would need to find some kind of method of sampling the audio signals so that in the least I could rig up a circuit that would trip an alarm if a certain frequency/amplitude was no longer picked up (I'm basically listening to pump sounds and need to ensure that everything is going well non-invasively, sound appears to be the best parameter)

 

[donkey]

you could also buy a very simple phone make a device that attaches to it then have that bluetooth or wifi to your other phone. wifi will get you heaps of room to transmit data and sound plus a few movies lol. the added bonus of this is you could get a higher end phone like an iphone 4g and use its cpu to do a few equations for you. then the majority of your work is programming.

fm will give you sound that is definate, but what sort of data were you looking at sending? depending on what type and how much you could find that you might have to have multiple channels.