display simple text from PureData?

Remork

scratch that.

i think the ATX power supply, while a promising solution to all my powering needs on paper, is just not suitable.
i tried running everything off of it, and sometimes it works, sometimes it doesn't.
which is no good.

switched over to another PSU for the 12 display line, with Bela still on the ATX 5v line, and bela wasn't properly booting (it opened the 12v line for a second, then crashed. and repeated that cycle.)

the minute i plug in the USB from the laptop, all is well.
now i have it running just on the USB as a power supply and Bela does its job perfectly.

so far for the ATX.. i think its 5v line is just not clean, stable or regulated enough.
only thing i can try is putting a 5v regulator on one of its 12v lines myself.
if that doesn't work, then i'll need to come up with some other, foolproof solution.

giuliomoro

Remork only thing i can try is putting a 5v regulator on one of its 12v lines myself.

That could work, if it has enough current (about 200mA @ 12V with a switching regulator). I recommend using a RECOM R-785.0-1.0 regulator, it serves us well on Pepper and Salt for 12V -> 5V conversion.

Remork

yeah well.. i tried a 7805 (which should be more than ok for those kinds of currents) but the switching noise underneath just becomes unbearable. let's just decide that ATX supplies and audio are not the best combo 🙂
will give Bela a dedicated wall wart. quickest and easiest..

giuliomoro

Remork (which should be more than ok for those kinds of currents)

Well, the current is actually 400mA, so a linear regulator like a 7805 going 12V -> 5V quickly becomes a portable heater. A switching regulator would require less current and generate less heat. However it's probably going to be at least a bit noisier (even though the RECOM above is pretty good).

Remork ive Bela a dedicated wall wart. quickest and easiest..

yes

Remork

giuliomoro you could try adding a 4k7 pulldown to ground from each of the HP out channels to ground. We added that in the latest revision of the cape, but it may not be 100% effective.

good enough!

giuliomoro

brilliant!

Remork

not quite there yet. jeeesus h christ.

i got rid of a lot of noise by moving the fan for the ATX from the 12v line (on PWM) to the 5v line, which i'm not using.

only noise i hear now, changes with the content of the display 😠
when the display is black (aka not showing anything), there's hardly any noise.
when i display letters or numbers, i get noise. noise varies, i'm guessing with the number of active pixels.

weird thing is: when i unplug the cable from bela to the amp on Bela's side, it's dead quiet.
i would expect a loudish hum from a cable hanging loose, but no.

i could try to work out where the display noise is coming from, but i'm getting quite fed up with the whole thing TBH. if it's quiet when unplugged and the noise is masked when playing audio, i'm thinking of switching the audio lines. should prevent the pop as well.

sigh. not the easiest project, this one.

is there an analog gnd/ digital gnd separation on Bela i'm overlooking?
the display noise might actually be creeping through the ground portion of my BS170/relay setup.
the relay is supposed to be completely separated, but i do have a common ground point on P9.1.

giuliomoro

Is this a big Bela? P8.01 should be a digital ground, while P9.01 and the others are more noise sensitive if I remember correctly

Remork

yes, big bela.
will try moving that gnd point to P8.01 tomorrow then.

only time it was a lot more quiet was when i was running Bela on usb from the laptop battery, so that points quite strongly towards a grounding issue. will have to doublecheck my grounding scheme.
done for today.

Remork

tried some combo's, lifting grounds etc.
moving the relay assembly driving the display to P8.1 definitely helped.
doubled up the return (ground) wires for both amp and display.
in the end the best solution seems to be to run both the display +12v from its own (two-prong) power brick, and the lightbulbs (indeed..) on their own separate supply, to get the noise down to a more than acceptable level.

not all too surprising, maybe.. i'm running Bela audio to an external power-hungry amp to reach jukebox levels, i'm using a low-side mosfet to switch on a couple of 12v LED light bulbs when you push the button (totalling over 3A), and you have the power- and datalines of the display in there as well.. so it's a bit of a spider's nest of possible ground loops with fairly high currents. i can probably only take this so far, and using a single noisy ATX supply was a bit too much wishful thinking. the ATX is fine for powering the amp, though, as long as nothing else is on there to mess up the power lines.

giuliomoro

Remork moving the relay assembly driving the display to P8.1 definitely helped.

good!

Remork l power-hungry amp to reach jukebox levels

I am wondering if you are leaving precious dBs on the table there ...:

are you using the headphone output? In that case make sure you set the headphone output level to 0dB instead of the default -6dB
does your power amp have balanced inputs? In that case, you could use the balanced line out on J9 (see here https://github.com/BelaPlatform/Bela/wiki/Hardware-explained#unpopulated-pads ) and drastically improve the SNR. These are DC-coupled, but as long as the inputs are AC-coupled (99.9% likely that they are), you can connect them directly without a need for a series capacitor (these are the codec's bare output pins, no resistors and no capacitors in series, so treat them with care).

Remork

giuliomoro make sure you set the headphone output level to 0dB instead of the default -6dB

will doublecheck!

giuliomoro does your power amp have balanced inputs?

nope 🍗 (wanted to use 'pout' and found 'poultry leg.')

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