Author Topic: Homemade Bluetooth Module  (Read 9988 times)

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Offline airman00Topic starter

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Homemade Bluetooth Module
« on: October 01, 2008, 06:29:58 PM »
I will need a bunch of bluetooth modules and I don't want to spend 40 bucks on each module as I will need like 10 of them ( reveal details later ;)  )
Here is the module : http://www.sparkfun.com/commerce/product_info.php?products_id=8474

Basically I want to make a knockoff of their version for my own robots - but at a lower price. I don't need to stick to their chipset , I just need to get the job done .

Can anyone suggest a different(and cheaper) bluetooth chipset to look at to make my own bluetooth UART module. ?

Thanks,
Eric
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Offline dunk

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Re: Homemade Bluetooth Module
« Reply #1 on: October 01, 2008, 07:05:40 PM »
hey Airman,
to my knowledge bluetooth is based on a proprietary software stack so you need to pay the owner royalties to implement the bluetooth stack.
that's not to say there are not chipsets available for sale that have factored that cost into the price
but in my opinion the chances of you putting something together for less than $40 is low.

you might fare better designing a non bluetooth RF link between your PC and the client nodes. (i'm presuming here you want bluetooth control from your PC.)
something along the lines of USB-UART chip to RF transceiver module plugged into your PC
and then just the transceiver module connected to microcontroller UARTs on the client nodes.
obviously i'm making some assumptions about your application here.


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Offline TrickyNekro

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Re: Homemade Bluetooth Module
« Reply #2 on: October 02, 2008, 10:35:59 AM »
To my knowledge bluetooth works at 2.4GHz
So if you can run the protocol with a processor and have a module to transmit over then you can get it do....
I think I found somewhere some notes about bluetooth protocol...

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Offline Trumpkin

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Re: Homemade Bluetooth Module
« Reply #3 on: October 02, 2008, 10:45:35 AM »
Making a swarm?
Robots are awesome!

Offline airman00Topic starter

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Re: Homemade Bluetooth Module
« Reply #4 on: October 02, 2008, 05:32:41 PM »
Thanks for the replies guys

but in my opinion the chances of you putting something together for less than $40 is low.

Where would the cost lie? Lets assume I can get the board milled for free , now how difficult/ time consuming and expensive would the bluetooth module be . Keep in mind I would need between 10-20 of them .


Also I chose bluetooth because it seemed the easiest at the time - doesn't it autochannel so no interference? Also a dongle would be able to connect to up to 7 simultaneously. If you can provide some more details on making RF have the same transmission properties(no interference and multiple devices per dongle) , I would really appreciate that .

Side note : Bluetooth is RF , isnt it? Like TrickyNekro said , its 2.4Ghz. Right?

@TrickyNekro
I would really appreciate your notes on the bluetooth protocol
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Offline dunk

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Re: Homemade Bluetooth Module
« Reply #5 on: October 03, 2008, 04:20:49 AM »
Quote
Where would the cost lie? Lets assume I can get the board milled for free , now how difficult/ time consuming and expensive would the bluetooth module be . Keep in mind I would need between 10-20 of them .
bluetooth uses RF as a transmission medium.
it can change it's operating channel (frequency) to find one that is not being used much.
transmissions bust be addressed to specific receiving nodes so all nodes receiving the transmission know which one it is destined for.
as it's a 2 way system each node will need a transmitter and a receiver. not just any transmitter either. it will need to be able to power down while the receiver is in use and power up (within a few microseconds) when it needs to transmit.

so while it would theoretically be possible to build radio transmitters and receivers with the desired properties if you want anything like high speed communications you will have to buy the radio part.
try looking for "RF transceivers". you would need one that operates at the same frequencies as other bluetooth devices.
as well as the radio you will need some sort of microcontroller to handle interfacing with the bluetooth stack.

i seriously doubt you will be able to buy the components requires to communicate with other bluetooth devices for under $40 and you would not yet have started trying to reverse engineer the software side of the blutooth stack.

Quote
Also I chose bluetooth because it seemed the easiest at the time - doesn't it autochannel so no interference?
less interference but as there are still only a limited number of channels there will still be times you are sharing a channel with others.

Quote
If you can provide some more details on making RF have the same transmission properties(no interference and multiple devices per dongle) , I would really appreciate that .
this is not an interference issue. it's an addressing issue.
just transmit an address byte at the start of every data packet. if a receiving node sees a packet come in have it ignore any that are not addressed to it.
interference will still happen. you will need some sort of checksum to make sure you got the whole packet.

Quote
Side note : Bluetooth is RF , isnt it? Like TrickyNekro said , its 2.4Ghz. Right?
bluetooth communicates over RF but it is more complicated than that.
bluetooth has all the addressing and pairing side of the protocol as well.


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Offline airman00Topic starter

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Re: Homemade Bluetooth Module
« Reply #6 on: October 03, 2008, 05:51:51 AM »
Thanks dunk

I took your advice and tried an RF link. I send a dummy byte,address,data,and then checksum. Everything seems to work well enough.
I found this tutorial helpful regarding data transmission over RF link.  http://winavr.scienceprog.com/example-avr-projects/running-tx433-and-rx433-rf-modules-with-avr-microcontrollers.html
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