Parasite noise on atmega328p outputs

Go To Last Post
12 posts / 0 new
Author
Message
#1
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hi. I am making a musical sequencer module.
I have an atmega328p inside a sequencer device that sends triggers which are square pulses to an amplifier in bassdrum module. Both devices are connected to a one common power rail. Sequencer device is also uses a HT16K33 led driver to drive a led matrix with i2c protocol. The problem is that there is a feedback through a power rail that goes back to sequencer and adds a parasite noise to a signal. That occurs only when a HT16K33 is working. On an image you can see 2 ms squares and parasitic noise in between.

Attachment(s): 

Last Edited: Wed. Nov 13, 2019 - 02:40 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I think you are going to have to post a schematic before any of the sparkies here can comment on the electronic design and how to filter/suppress noise.

Last Edited: Mon. Nov 11, 2019 - 11:47 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

My first port of call would be the power wiring. All wires have resistance, capacitance and inductance. Depending on the supply, the wire and the load determines is the wiring is adequate. The led driver is switching the led current. How much is this? What is the resistance of the wire? Ohms law will tell you the voltage drop. Is this what you are measuring?
Then we can factor in the switching frequency of the leds and estimate the inductance. Does this explain what you are measuring?

The other fundamental clue is current flows in a loop. How is the current flowing in your circuit? Thus how you interconnect various things has an impact. You don’t want your trigger path in your led current path.

Show us a picture of your layout. We want to see your power supplies. Once we have some information we can them be better place to give you solid advice.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

thanx for reply! I have attached schematic images.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

power supply is a common eurorack power supply, which is +12v and -12v. 1000 mA. Sequencer power consumption is 120 mA. 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0


 

You are missing a pulldown resistor on the OUT jack signal...this will cause the output to  float around & appear like "noise"

 

Add a 1K to GND & you will be ready to play the banjo.

 

also, are you drinking heavily?  These symbols are all pointing in the wrong direction---WHY?

 

 

also note D15 should be on the left side of Rxx  (where are your part designators ??), or it will burn up upon negative voltage protection 

 

The following is another example of goofball drawing... NEVER cross two wires like this & maybe use a dot...are these connected or not?  Who knows?

 You are supposed to use a T intersection only.     Pay close attention to details.

 

  

 

 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

Last Edited: Mon. Nov 11, 2019 - 07:10 PM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Thanx for pointing to my drawing flows. But unfortunately we tried already to pull down outs as you describe. it didn’t help. Also an internal pull-up resistors are on. It should be mentioned, that this feedback occurres only with this bass drum module. Otherwise, outs on sequencer are clean.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

You show all the output lines of the HT16K33 connected together.  If the HT is causing the problems, take it out of the circuit.  Why do you need 128 LED (always capitalized) segments for a bass drum emulator?

 

The output of the AVR doesn't need any diodes or resistors.  It's only a +5/gnd square wave signal. It doesn't need any negative voltage protection and it is not connected to +12V.

 

The BD analog module looks like a fine mess. It must be something from a 1970s-era build-it-yourself synthesizer book that someone scanned and posted on the web.  Do you have any idea how it works? Or are you going on blind faith that once you spend hours wiring it and checking the wiring, then it will do...uh...something.    It has many inputs besides a trigger pulse.

 

I recommend for people wishing to explore to explore music/synthesizers/sounds with microcontrollers to get either a real MIDI tone module (about $100-$200 on eBay, but resellable at the same price), or an Arduino UNO and a VS1053 shield ( for about $10-$20 on eBay).  The VS1053 sound IC has an internal General MIDI synth (with 128 ROM sampled instruments) which will accept MIDI commands to play notes.  Real analog synthesizers (Moog-style "subtractive synthesis" units) will cost in the $1000 to $50000 range.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0


you MUST have a pulldown...what do you expect to make your output go low? 

Maybe where it connects will do that, but that is a bad choice...and you don't show the setup.

 

Also, make sure all your diodes are schottky, so you don't creep  too close to the logic thresholds...no sense throwing noise margin in the trash.

 

 

 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

The VS1053 sound IC has an internal General MIDI synth (with 128 ROM sampled instruments) which will accept MIDI commands to play notes

Jeepers, the next $2 chip will be able to beam the music electronically straight into your head. 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Simonetta - I got myself a Behringer model D recently. Probably around $300 usd. Virtually a direct copy of a miniMoog. There are other cheap analog synths.

Yes, you need protection for the AVR outputs - weird stuff might happen when you are live patching.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I'd guess that a general purpose rack mount power supply, +/- 12V @ 1A, uses switching regulators these days.

 

The BD unit is a cool analog circuit, but I suspect it will do better with a very clean power supply.

I'd consider using a 12 V linear regulator, (with an appropriate Vin, and a heat sink).

 

Mixing digital and analog audio on the same PCB with a shared power supply is certainly doable, one just has to be very careful.

As mentioned above, the ground current paths can be as important as the V+ supply in this case.

 

JC