• Guest, The rules for the P & N subforum have been updated to prohibit "ad hominem" or personal attacks against other posters. See the full details in the post "Politics and News Rules & Guidelines."

What's the protocol for pairing two bluetooth devices without screens?

fuzzybabybunny

Moderator<br>Digital & Video Cameras
Moderator
Jan 2, 2006
10,455
33
91
The "normal" way of pairing bluetooth is easy - put both devices into discovery mode, wait for the bluetooth device to show up on the screen, select it, enter passcode, and done.

But what if you have two devices and neither have a screen, much less a keyboard of any kind? Like a bluetooth transmitter that takes an AUX-in from an MP3 player or whatever, and a bluetooth receiver that has an AUX-out into some speakers?

Do these two need to be hardwired to search for and ONLY pair to each other when in discovery mode, meaning they must be the same brand and made explicitly to work together? Or is there a standard protocol for screen-less bluetooth devices to pair, regardless of their make and model?
 

lopri

Elite Member
Jul 27, 2002
12,842
325
126
I am curious about it as well. It seems like you are counting on the chance of time/place where the two devices are in discovery mode. (?)
 

fuzzybabybunny

Moderator<br>Digital & Video Cameras
Moderator
Jan 2, 2006
10,455
33
91
I am curious about it as well. It seems like you are counting on the chance of time/place where the two devices are in discovery mode. (?)
Yeah. And what happens when three+ screen-less devices from different manufacturers all happen to be in pairing mode (perhaps in a crowded place) at the same time, but you only want your device to pair with one of the other two, but you've got no screen or controls on the parent device to select which of the other devices to pair to? I'm going to assume that the device just pairs to the first device it detects in discovery mode, if pairing between two unmatched brands is possible at all.
 

fuzzybabybunny

Moderator<br>Digital & Video Cameras
Moderator
Jan 2, 2006
10,455
33
91
Well, after doing some more research I think I've figured it out:

https://learn.sparkfun.com/tutorials/bluetooth-basics/how-bluetooth-works

Bluetooth is strictly a master-slave network. There is one master that can connect to multiple slaves. Slaves cannot connect to other slaves.

Slaves broadcast out their credentials in pairing mode. The master looks for these credentials in pairing mode.

Two slaves would thus only be broadcasting and will never pair, so screen-less Bluetooth devices are probably mostly all slave devices.

For screen-less Bluetooth transmitters and receivers, one has to be preconfigured in their respective firmware to be a master and the other the slave. It's logical that for most situations, the transmitter is the master while the receiver is the slave. Looking at the code for some Bluetooth chips, it seems that you have to program ahead of time which mode you want which chip to be in.

This explains why, for instance, the new GoPro 5 with built-in Bluetooth can only pair with a phone and not with Bluetooth mics or headphones, despite having a user interface that could clearly select from a list of discovered devices. The GoPro was manufactured as a Bluetooth slave. I supposed they could offer a firmware update to allow for a user interface to change the master/slave mode of the GoPro to allow for pairing with different devices, but my guess is that this would be a horrendous user experience - changing the GoPro to slave would allow it to connect to a Bluetooth mic, but would remove its ability to connect to a smartphone, something users wouldn't be able to understand. The only option to have slave and master running at the same time would be to have two separate chips.

It's also possible to program the chip to only connect to another chip of a certain address (fixed address connection), which explains why there are some Bluetooth transmitter/receiver pairs that are bonded to each other and will not connect to other Bluetooth devices, even other pairs of the same make and model.
 
Last edited:

Zaap

Diamond Member
Jun 12, 2008
7,162
423
126
Why do people always do this? "Just google it! How dare you ask a question!"

It's a forum. Sure, sure, we could all just google everything and never discuss anything, then I suppose there'd be no threads. Not sure how that would make for a better forum.

It's more interesting for some to ask questions from others who know about the subject, than only google stuff. A lot of times googling lands people on forums anyway. Sometimes with very specific topics, that's the best place for answers. Why not just start where you may end up in the first place?
 
  • Like
Reactions: WelshBloke

Red Storm

Lifer
Oct 2, 2005
14,207
216
106
Why do people always do this? "Just google it! How dare you ask a question!"

It's a forum. Sure, sure, we could all just google everything and never discuss anything, then I suppose there'd be no threads. Not sure how that would make for a better forum.

It's more interesting for some to ask questions from others who know about the subject, than only google stuff. A lot of times googling lands people on forums anyway. Sometimes with very specific topics, that's the best place for answers. Why not just start where you may end up in the first place?
Agreed. A lot of Google searches take you to forum posts asking the same question you searched for, and it's there you often find the answer.

I learned something new from OP's follow up post, and I'm sure others who search for a similar topic and end up here will as well.
 

fuzzybabybunny

Moderator<br>Digital & Video Cameras
Moderator
Jan 2, 2006
10,455
33
91
Why do people always do this? "Just google it! How dare you ask a question!"

It's a forum. Sure, sure, we could all just google everything and never discuss anything, then I suppose there'd be no threads. Not sure how that would make for a better forum.

It's more interesting for some to ask questions from others who know about the subject, than only google stuff. A lot of times googling lands people on forums anyway. Sometimes with very specific topics, that's the best place for answers. Why not just start where you may end up in the first place?
To answer your question of "why do people do this," it's because Capt Caveman is a useless dick. Always has been over the years, so he's going back to being blocked, which pleases me.

Now, on the subject of "being useful and not a dick," I'm going to confirm what I've learned by asking on the Stack Exchange EE forums since I find that information like I posted above can often change depending on how people decide to engineer products in real life. Bluetooth has the master-slave limitation, but perhaps there's some industry-standard design pattern or profile I don't know about that finds a way past this. A single chip by itself has the capability of functioning either as a slave or master - it's the code that sets the mode - so perhaps some devices have clever ways to swap modes?
 

fuzzybabybunny

Moderator<br>Digital & Video Cameras
Moderator
Jan 2, 2006
10,455
33
91
You mean like a display and controls? ;)

Simple devices probably were designed by their manufacturers to be BT slaves and nothing more.
Yeah, I'm going to say that any kind of simple consumer device that's intended to be paired to a smartphone is probably going to be in slave-only mode, because getting it out of slave mode would involve a physical addition to the product, such as, at minimum, a single button or a switch.

In my case it's a little bit more complicated. I've got a Sena transceiver that motorcyclists use to talk to each other. Each Sena takes audio from a wired microphone and sends it to another Sena. It also takes audio received from other Senas and outputs it through a headphone jack. It also takes audio received from devices such as GPSes and smartphones and outputs it to the headphone jack. And it takes audio from the mic and outputs it back to the smartphone.

I thought I was being clever by buying a bluetooth audio receiver that outputs to a headphone jack. I was going to use the Sena to take audio from the mic and then transmit that via bluetooth to the bluetooth receiver which would then send the audio to a camera via the headphone jack. But of course the receiver is a slave and the Sena is apparently a slave as well.
 
Last edited:

lopri

Elite Member
Jul 27, 2002
12,842
325
126
This is a fascinating stuff. Thank you for the follow-up with your finding.
 

victorhugodoy

Junior Member
Aug 21, 2020
3
0
6
I want to pair a Victrola Bluetooth turntable to a Ultimate Ears Wonderboom bluetooth speakers, but I can`t. Any ideas? Both don´t have screens.
 
Last edited:

Cogman

Lifer
Sep 19, 2000
10,274
121
106
I want to pair a Victrola Bluetooth turntable to a Ultimate Ears Wonderboom bluetooth speakers, but I can`t. Any ideas? Both don´t have screens.
Not going to work (without extra equipment) for a couple of reasons.

First up, it's a slave device (like fuzzybabybunny points out). Slave devices can't interact with other slave devices (like your speakers).
Next up, it doesn't have the ability to broadcast audio, only to receive audio (It can play sounds coming from your phone but can't receive from that same device).

Now, there's an alternative. You can use a bluetooth transmitter (because this has a headphone jack) and pair that way. I can't tell you how easy that is to work with.

 

victorhugodoy

Junior Member
Aug 21, 2020
3
0
6
Not going to work (without extra equipment) for a couple of reasons.

First up, it's a slave device (like fuzzybabybunny points out). Slave devices can't interact with other slave devices (like your speakers).
Next up, it doesn't have the ability to broadcast audio, only to receive audio (It can play sounds coming from your phone but can't receive from that same device).

Now, there's an alternative. You can use a bluetooth transmitter (because this has a headphone jack) and pair that way. I can't tell you how easy that is to work with.

Thank you, Cogman! I didn't expect that... What's the point of a bluetooth turntable that is a slave? It is not supposed to broadcast audio to bluetooth speakers?
 

mnewsham

Lifer
Oct 2, 2010
14,482
398
136
Thank you, Cogman! I didn't expect that... What's the point of a bluetooth turntable that is a slave? It is not supposed to broadcast audio to bluetooth speakers?
As they say in the amazon listing
EXPANDED CONNECTION OPTIONS - Stream smartphone audio through the turntable’s built-in Bluetooth speakers.
So they're specifically advertising it as a wireless speaker for your smartphone, not to allow you to output vinyl audio via bluetooth.
 

ASK THE COMMUNITY