Audio Testing

[AllanBirt]

Just done some more testing today with a friends PAW at home and you also get some background noise, this starts from once powered up. Now after putting my fingers either on the Ethernet port or the metal section round the PAW aerial not the ADSB one, this noise disappeared, so earthing seem to resolve this.

Is this recommended or should I live with this noise as I see the PAW is not causing this, its being caused by the Raspberry PI board itself :-(

[brinzlee]

Ok I have tried my Bose A20 Bluetooth and they are fine with the lead connected to the rPi and the A20 control box, completely silent apart from traffic alerts of course....I made my lead using the 4 pin plug and not the stereo plug that shorts out the video so I am not sure if that makes a difference.....I also have a bluetooth adapter that I plug into the rPi audio output and that injects audio via bluetooth into the  Bose A20 without any leads and that works a treat..my preferred connection. Its such a tiny unit and sits on top of the PilotAware....I hate wires !!

Are you using a battery or aircraft power and step converter to power the PilotAware ?

Regards
Brinsley

[AllanBirt]

Hi,

I'm using aircraft power and one of these as per the link. https://www.amazon.co.uk/Anker-Charger-Adapter-PowerDrive-Samsung/dp/B00VH84L5E.

Its great that you don't get any noise, I've tried the audio jack that's supplied with the BOSE A20 and I have also tried a different cable like the one you would use to connect sound card from a PC to a the speakers within a monitor and get the same result.

I don't have any low down noise if I plug a mobile device in, only the Raspberry PI boards.

I'm running the latest PAW software too, I've even tried a new Raspberry board with nothing installed and once powered get this same low down noise coming through. It goes quite if you touch any USB, LAN, HDMI part thus earthing them.

It's like hissing sound, it's low in volume but you can here it, until the board is earthed.

I see you made your cable, I was looking at doing the Bluetooth connection, but like the idea of keeping that free in case I fancy some music as the AUX connection gets priority  done some testing and works well 

[exfirepro]

Hi Alan / Brinsley,

When I first connected my PAW to my Flycom intercom way back in early testing days, with the PAW running on a battery pack, I had no problems whatever with a made up 4-pole TRRS jack to mono phono plug as here

http://forum.pilotaware.com/index.php/topic,376.msg5117.html#msg5117

http://forum.pilotaware.com/index.php/topic,420.0.html

Unfortunately, when I connected the PAW to aircraft power I started to get significant background 'computer sounding' audio interference which was coming from the Raspberry Pi. Like yours, this disappeared if I touched the Pi metalwork with my hand. After discussing this with Jeremy Curtis and on his advice, I re-wired one of my leads to short the outer audio cable 'screen' (which transfers video out from the Pi in the [Maplin] cable I was using) to ground and have had no problems since, despite the fact that this means that (contrary to Jeremy's latest advice above), the cable 'screen' is effectively grounded at both Pi and Flycom ends.

Certainly in my experience worth trying grounding the screen (at least at one end). This doesn't seem to bother the Pi at all.

Regards

Peter

p.s. Brins, could you post link to where you got your bluetooth unit - it certainly looks pretty sound.

[Keithvinning]

Have you tried using ferrite cores on the power lead

http://uk.rs-online.com/web/p/products/7413056/?grossPrice=Y&cm_mmc=UK-PLA-_-google-_-PLA_UK_EN_Passive_Components-_-Ferrite_Cores&mkwid=sa0YjBZMt_dt%7Cpcrid%7C88057072923%7Cpkw%7C%7Cpmt%7C%7Cprd%7C7413056&gclid=CMvB3M_CptECFQg6GwodglEKzA
When I was looking at amplifying the output of the Pi I got a clicking sound which seemed to be induced from the Psu. Worth a try. Make sure the firrites that you get fit snugly round the cable

[JCurtis]

If the hum goes away when you touch the ethernet socket, then it really sounds like a ground loop.  Probably caused by a poor earth on the power feed or the audio system somewhere.  You could try an audio isolator and see if that fixes it.  It doesn't need to be much, even a slightly corroded/oxidised terminal can cause it.  Try rotating the power plug in the socket too, just in case there is a poor connection there?

https://www.amazon.co.uk/Ground-Isolator-HAVIT-Speaker-Filter/dp/B01IETQQQK/ref=pd_lpo_263_bs_t_2?_encoding=UTF8&psc=1&refRID=98GFXG3N5A2AJPZSVWYX

Like yours, this disappeared if I touched the Pi metalwork with my hand. After discussing this with Jeremy Curtis and on his advice, I re-wired one of my leads to short the outer audio cable 'screen' (which transfers video out from the Pi in the [Maplin] cable I was using) to ground and have had no problems since, despite the fact that this means that (contrary to Jeremy's latest advice above), the cable 'screen' is effectively grounded at both Pi and Flycom ends.

The thinking here was to ground the video out, to prevent it causing issues.  It isn't signal ground that should be only at one end, but any cable shield.  Depending on the quality of the cables some skimp and use the cable shield as signal ground too.  The shield should only be connected to ground at the audio output end.

edit: I notice that Amazon has popped up that people who buy the Anker PSU also often buy the isolator too.  Might have to dig out the one I bought and run some tests when I get some time...

[brinzlee]

As Jeremy suggests possibly a ground loop. I never liked the idea of shorting the video pin with a stereo 3.5mm jack.....but plenty do and have no issues. CPC sell the correct 4 way 3.5mm jacks, I buy a stereo to stereo pre-made lead then cut one of the plugs off and re terminate with the new one..........

Have you tried a battery on the PilotAware that would rule out the ground loop, if it still does it I would suggest checking the continuity on the screening on the cable to either end of the 3.5mm Jack.

And Peter here is the link for the Bluetooth Adapter......works great for the Bose A20 Bluetooth or when ground testing a I uses a wireless Logitech Speaker.....A single charge lasts about 8-9 hours.....and uses bluetooth v4.00...Perfecto !!

http://www.ebay.co.uk/itm/2-in-1-Wireless-Bluetooth-Audio-Music-Transmitter-Receiver-Adapter-Two-Way-A2DP-/272048764056?hash=item3f575eb498

[AllanBirt]

Have you tried a battery on the PilotAware that would rule out the ground loop, if it still does it I would suggest checking the continuity on the screening on the cable to either end of the 3.5mm Jack.

Tried using a power pack instead of mains power and yes no background noise, but I would prefer plane power 

Out of interest does the Bluetooth option resolve this, although I would prefer the wired option

[brinzlee]

If you have a ground loop caused by the aircraft power supply and the heaphone shield then I guess having no hard wired lead between the raspberry pi and the headset has to remove the ground loop....Its worth a try....the bluetooth transmitter is a cheap box to buy.....it might be worth a try.....although if it were me I would like to fault find and find the cause first..

[AllanBirt]

Hi Brinsley

Thanks for the info on the ground loop, but I also get this at home when using a power supply. My aircraft just been built and I don't get other noise like transponder, fuel pump or even when I power up my iPad via USB. I only get this low down hum when I use PAW for warnings. I have read up on another forum that this seems to be a common issue with the Raspberry Pi. What I've done in the meantime is ordered one of those ground loop isolator as recommended so finger crossed my problem will disappear 

Ive tried a ferrite on power supply and also on the aux lead and that's made no difference, the cable I'm using has 3 pole connection, so the only thing I've not tested is a 4 pole connection.

Regards

Allan

[brinzlee]

It really does sound like the lead to me....Where did you get it from....where are you based ?....maybe another User can lend you their lead as a quick check.....Have you got a powered speaker you could try the lead into instead of the headphones...just trying to rules things out.....If you are still getting the hum at home I presume the A20 has only one signal from the 3.5mm jack from the rPi and that you haven't got the two aircraft jacks or lemo plugged in......if that's the case its not a ground loop.

[AllanBirt]

Hi Brinsley

I think you may have resolved my issue, i have only tried the one cable within my aircraft, and that's the one supplied with my Bose A20 headset. I've tried another cable at home and was getting the same result, so automatically assume this would be the same in my aircraft :-). And yes when i am at home i don't have the GA sockets plugged in so yes i get the humming sound but if i plug into my amp all goes away. I will try and test this other lead when i pop up to Sywell over the weekend and fingers crossed all will be ok.

Out of interest both these leads are 3 pole 3.5mm sockets, should i be changing, or even trying a 4 pole socket cable as i know the Raspberry Pi 2 also transmits video, but if plugging into my bose headset surly these will be connected together, ie ring 2(ground) & sleeve(video) ....



If so i will need to purchase one of these and try..

Regards

Allan

[exfirepro]

Allan,

I have always used a [Maplin] 4-pole TRRS 'lead' - cut in half and adapted to a single phono plug for mono audio output at the other end to input to my Flycom Intercom audio input as per my May 2016 posts referred to earlier in the thread. On Jeremy C's advice, I shorted the outer braid 'video' to ground in a successful attempt to cure exactly the problem you are experiencing - i.e. computer 'hum' from the RPi coming through into the intercom. This effectively gives pretty much the same thing as a 'standard' stereo 3-pole TRS jack which 'automatically' shorts the sleeve to ground, so I'd be surprised if changing to a 4 pole makes any difference.

Probably best to wait and try your ground-loop isolator first.

Regards

Peter

[AlanG]

Brinzlee

Thanks for the link to the Bluetooth TX/RX adaptor, I took delivery of one today and I now have the choice of alerts from the PAW audio as well as the EVFR audio from my tablet wifi, straight into my intercom box with no wires trailing around.  Still to test on the aircraft but transmits PAW audio into my Bluetooth receiver with a set of headphones plugged in.  It works in the aircraft from the tablet so can't see why it wont work with the PAW.   

Cheers
Alan

[Ian Melville]

What is the situation regarding the clipping of the first part of the alert, when on BlueTooth?

Or is that what the background hum is for