What electronics do I need to insert between the analog audio mixer output and dongle pins 8 and 9 ???

Thread Starter

SmokerinCB

Joined May 13, 2021
19
Gentelmen ….. sometimes I attend events that involve private aircraft and event communications are on multiple VHF frequencies …. and I’m at these events with up to 20 friends ….. what I’ve got in mind is an RF/audio system that takes the audio output from multiple (maybe up to four) pocket size VHF receivers, runs those outputs thru a passive mixer, and that output goes to a Bluetooth dongle ….. or dongles, as the case may be …… I’ve considered running the mixer output to a low power FM transmitter but everyone seems to already has Bluetooth ear pieces or headsets …. and dongles are inexpensive ….. and their 30 foot range is more than adequate ….. the VHF receiver headphone audio output is via a 3.5 mm stereo jack ….. the audio, when the receiver is in the VHF mode, is mono and of limited frequency response … nothing fancy ….. each VHF receiver has its own self-contained battery so no power requirements there …. the mixer is passive so no power requirements there …. so I just need 5 volts for the dongles …. that’s easy …. LM7805 …. looking at the USB 3.0 pinout – I’ll need to use pins 1 and 4 for power and connect the mixer audio output to pins 8 and 9 and ground (pin 4) …. the question of the day is – “What electronics do I need to insert between the analog audio mixer output and dongle pins 8 and 9 ???” ….. probably will include an A to D converter ....

Thanks ….
 

KeithWalker

Joined Jul 10, 2017
2,095
Which dongles (Bluetooth transmitters, I assume) are you planning on using? What is the audio input connector and signal level requirements? They are available with 3.5mm stereo audio input jack socket and standard audio line level input. That would just need direct connection with the output level of the mixer adjusted to a suitable level. The USB connector is just for 5VDC power. They work well on a power bank. If you are in no hurry, you can get them from AliExpress for a third of that price.

https://www.amazon.ca/PNGKNYOCN-Blu...ooth+Audio+Transmitter&qid=1635996389&sr=8-30
 
Last edited:

Irving

Joined Jan 30, 2016
2,422
Yes, but they are dumb devices and rely on a whole Windows infrastructure to convert audio to a digital datastream and pair with a single remote device. You aren't going to replicate that with a couple of chips on a breadboard any time soon....

You might be able to do something with a Raspberry PI, but streaming audio to multiple dongles might be taxing. Most systems assume only one audio stream end-point per system. I'm not even sure how you would set that up on a Windows laptop....
 

Thread Starter

SmokerinCB

Joined May 13, 2021
19
Irving ..... good morning ...... so that's not a good idea .... oh, well ..... thanks ..... now that device that Keith proposed does what I need ..... audio in and Bluetooth out .... and transmit only .... so what's in the middle ..... I might just have to buy one and take it apart .... it'll tax my DPA skills but it mght be worth a try ..... any suggestions ? ......
 

Irving

Joined Jan 30, 2016
2,422
Whats in the middle is a custom Digital Signal Processor with ADC, storage, compression algorithms, a bluetooth stack, etc, etc. You couldn't begin to reproduce that functionality in a cost-effective manner and the chips aren't on general sale unless you're buying them in the millions. There are no shortcuts here...
 

du00000001

Joined Nov 10, 2020
86
Whats in the middle is a custom Digital Signal Processor with ADC, storage, compression algorithms, a bluetooth stack, etc, etc. You couldn't begin to reproduce that functionality in a cost-effective manner and the chips aren't on general sale unless you're buying them in the millions. There are no shortcuts here...
While certification can be nasty, these MCUs with BT modem are also available in small numbers. See e.g. https://www.ti.com/wireless-connectivity/bluetooth/overview.html
Another approach would to mate a (pre-certified) BT modem with the MCU of your liking.
Anyway - there's quite some software to write...
 

Thread Starter

SmokerinCB

Joined May 13, 2021
19
Wow !!! .... that's all way over my head ..... OK, I'm falling back to plan B ..... I found this on AliExpress ..... the price is right and a January delivery is OK .... it gets it's 5 volts thru the USB connector and gets it's audio via the connecting cable .... to shift from transmit mode to receive mode, just unplug it from the USB port and then plug it back in .... easy to use ..... so, the next questions are (1) how many of these things do I need to keep 15 guys happy ? .... each willl be bringing his own Bluetooth head set or earbuds or what ever - I have no idea what's going to show up .... the dongles will be in transmit mode only .... headsets are receive only ..... no two-way communication .... so, how many headsets can pair with a dongle ? .... I've seen all kinds of conflicting info/opinions on Google on this subject .... from 2 to 5 each .... or more ..... and (2) how far apart do the dongles have to be ? ..... RF interference ? ..... haven't found anything on that .....

https://www.aliexpress.com/item/329...lgo_pvid=2dec09f3-903b-4a03-a3a1-e60bce2d2484
 

RPLaJeunesse

Joined Jul 29, 2018
196
Its Bluetooth - One headset pairs with one transmitter. And running many transmitters in the same space may very well cause interference among them. You might be better off getting each user a small FM radio (with wired earbuds, no BT) and use an FM transmitter to do true "broadcasting".
 

Thread Starter

SmokerinCB

Joined May 13, 2021
19
Gentelmen .... thanks for the education ..... I'm moving on with Plan C .... I ordered an FM transmitter kit from Amazon this afternoon .... I think that I have all the parts that I need to assemble the mixer ..... should be able to cobble something together in a few weeks .... and do a smoke test .... I'll pass on my results .... thanks again for sharing your wisdom ....
 
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