Construction suggestions for MIDI synth project

T

tacertain

Member
Hey all -

I've been playing around with a Teensy for a MIDI synth project, and I am looking for some advice on physical assembly. I have been doing most of my prototyping with a breadboard and various components, but am starting to think about what I want to use for real. I just picked up new Teensy 4.1 and audio shield. I was thinking of using regular headers to connect them as shown below. First question: does this seem crazy? Second question: which way? It seems like it'll work better to put the audio shield on the bottom with the long pins running through the shield. If the shield is on top, the USB connector for the Teensy looks like it'll be contacting the audio shield across the mic/ground inputs. I'm not going to be using those, but that still seems less than ideal. Anything I'm not thinking through?

PXL_20250708_004133258.jpg


Because I'm using the board as a MIDI host, I want to use the USB host port. The easiest thing from my perspective is to solder a header onto that connector and use a PC motherboard USB connector. If the audio shield is on the bottom, this is simple - just put the USB header on the top.

Finally, I want to use a display. I've been playing around with one of these little ILI9341-based displays. The main problem I've been having is that the data transfer to the display causes audible noise out the headphone jack. I'm hoping that will be reduced by direct wiring the shield to the Teensy, but what other suggestions do y'all have? What would be the best way to connect the display inputs to the Teensy?

Any words of wisdom gratefully received!

Andrew
 
Have seen direct solder as such create issues where one board is damaged and then reuse of the other is hard at best. Must assure enough gap at a minimum to prevent shorts. PJRC demonstrated use was double row pin holder strips with a clear gap.

no doubt it has been done and likely works properly as long as no adds or edits are needed on T_4.1 bottom or Audio topside connections.

There are Low Profile pluggable headers that might suit - see Adafruit or ProtoSupplies [ https://protosupplies.com/product/header-set-low-profile-1x24/ ] . Those linked are minimally taller than what it shown - though bottom pins are too short to breadboard after, but are made to PCB mount.


Low-Profile-Header-Comparison-to-Standard-Header-3.jpg
 
Thanks for the thoughts. You're right that it would of course make changing anything very hard. I would love to be able to plug them together rather than solder. I suppose I could always put female headers on the Teensy and then plug the audio board into those.

Any advice about the best way to connect a display screen, especially to reduce electrical noise to the audio board?
 
If you aren't using a lot of the Teensy pins or plugging into a solderless breadboard, putting the audio adapter on the bottom can work OK so you have access to USB Host pins on top. I personally put the audio board on top so that that the full set of Teensy pins remain available.

Doing that does cover the USB Host port, but depending on your overall setup you do have the possible option to bring the pins down from the bottom as long as you remember to solder them on before mounting the Audio adapter, like this. Note that this assembly will no longer plug into a solderless breadboard if that is important to you.
1752339320566.jpeg


You do need to give a little space between the boards to avoid issues with shorting. Regular headers don't give you enough space to be safe. I use headers with extended pins that raise the Audio adapter up and then clip off the unused pins on the top-side of the rest of the Teensy. Here is an example of the type of pin I am talking about: https://protosupplies.com/product/header-male-1x40-break-away-extended-tail-gold/

If you prefer the Audio adapter to be pluggable, you can mount female headers to the bottom of the Audio adapter instead of soldering it to the pins. It will just make the assembly a little taller. Here is a mockup of what I am talking about.

1752338506552.jpeg

1752338522575.jpeg


This webpage might give you some other construction ideas: https://protosupplies.com/product/teensy-4-audio-stack/

As for audio noise with the LCD, make sure to keep the LCD data wires routed well away from the audio. Also, most ILI9341 operate at 5V and have a built-in 3.3V regulator, but some people try to run them at 3.3V which is not a good idea, especially if it is using the Teensy 3.3V output.
 
Hi,
I have tested a lot of mini displays. Unfortunately, they all bring a lot of noise. I have best results with 4 digits 7 segments TM1637 displays. Mini OLED displays are the worst and they often use blocking i2c libraries.
Emmanuel
 
Hi all -

Thanks for all the thoughts and advice. Just to follow up, here's what I did. I had another audio board (similar to this one) already soldered to headers, so I decided to give it a go first. Here's the setup with the boards:

PXL_20250718_173650154.jpg


And here is the wiring:

PXL_20250718_173723975.jpg
PXL_20250718_173733988.jpg


The I2S transmission wires are the two on the bottom and the SPI wires are routed on the top. I added 100ohm resistors on the SPI clock and MOSI lines. Everything is working and I am not getting any noise on the audio out. Please excuse the red ground wire!

Andrew
 
@tacertain good job on the build. It looks like you got all the key construction points implemented well. And of course the proof is in the fact that it is working!

@emmanuel63 audio noise from a display is typically due to the overall circuit design and construction and not due to the LCD itself. Main thing is to keep the display SPI and the audio signals short and routed away from each other and ensure everything has a good power and ground setup with nice beefy gauge wire like Andrew did in his setup. Adding series resistors on the SPI CLK and MOSI lines as he did can also help with a number of issues and is good design practice in general.
 
Just to echo what @KenHahn wrote, when I was using the same components with a solderless breadboard and the crappy wires that came with my Arduino kit, the build was /A/ super flaky, and /B/ generated a lot of noise when it did work. I decided to just make the time investment in soldering something up, routing the wires thoughtfully, adding resistors, etc, in the hopes that it would fix the problems, and it did! Everything just works (well, it does after tracking down a couple of weak solder joints) and works all the time.
 
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