Etch Eurorack Module Build

!!!AIR RAID SIREN EDIT!!!

Two things to address:

1) Cut those LED legs under the jacks so so flush. This footprint is bad, in that it allows any raised bumps there interfere with metal parts inside the jack. In one case, this caused a finished module to burn up one of its important parts.

2) There's a slightly better way to mount the OLED.

1. get the wires soldered to the corners of the OLED PCB, and install it in the main PCB without soldering the wires to the main PCB
2. put the front panel on the module
3. with the OLED touching the front panel, run some solid core (still bendy) wire to the electrical connections: the data and clock lines; and the +V and GND lines (pay attention to the OLED layout and use the matching pads on the PCB)
4. power up the module, fiddle with the rotary encoder to get to a screen that lets you see where the display portion of the OLED is so you can move it around so it's flush and square
5. power down the module and solder the corner wires to the PCB to lock the screen in place

Okay I hope this helps. The screen mounting is the most troublesome part of this project, with the jack footprint a close second.

Now... let's jump in!

This is the build guide for the Modular for the Masses Etch module. The module is a 10-bit bitcrush and sample rate reducer, and there's also a deep quantizer mode which comes along as a bonus! Please have a look at this project's Github to see some more wonderful details.

Here's what you'll need!

1. PCB and panel set
2. AVR128DA28-I/SO (this is the microcontroller, the number means: AVR = the family of chips 128DA is the name of this particular chip, 28 means it has 28 pins, I/SO describes the physical package
3. little pushbutton switches with a "clear hat" and an integrated LED. Here's the ones I use

Okay, so the above 3 parts might already be assembled, because the microcontroller is an SMD part which can be tricky, and the pushbutton needs modifying before assembly. You're welcome, maybe?

1. SSD1306 OLED screen -- the kind with 4 pins. The power and ground pins are not standard across all these, but this module can handle either kind.
2. Rotary encoder. With two nuts. Electronically, these aren't standard, some go one way some go the other. The software can be easily tweaked to handle that, so don't worry about this yet
3. 2 x 6mm x 6mm x 12.5mm tall tactile switches
4. 3 x 100K JuanitoPots -- these are potentiometers with clear shafts that you'll need to get from me, I guess I had them custom manufactured. You can use another type of potentiometer if you can't find me.
5. 1 x 100K sealed rectangular pot, the basic R09 type
6. 2 x 100K box-style precision multiturn trimmers with the adjuster on the top
7. 5 x Thonkiconn mono audio jacks. I use these very high quality ones. Also you'll need nuts, knurled or hex, whatever's your kink.
8. 8 x 3mm LEDs, any color. You probably can find these tangled in your carpet or in your dustpan.
9. Several lengths of solid core bare copper wire. I get it from old network cables

Also you'll need a soldering iron, solder, wire clippers (FLUSH CUT, this is important), pliers... you probably know all this already :)

Here's what the AVR128DA28-I/SO looks like already installed. Look up "drag solder SMD" and watch a bunch of videos if you need to do this yourself. Don't omit flux, flux is really important to get the connections reliable and avoid solder bridges. Flux is kinda magic

The second picture shows how you have to snip off the plastic protrusions on the bottom of the pushbutton switch. It sits up a bit too high for the other components we're using. Sharp wire clippers like this will work, but you can carefully file them down as well like in the picture

Problem is?? that you'll be removing the locator tab. Keep track of which LED leg in the pushbutton is +, and which is -, and install the pushbutton to match the PCB footprint.

Bend all your LED legs like this. I hold the LED body in my pliers with my right hand, with the legs to the left of the tool. The longer LED leg goes on the bottom because it's heavier and gravity.

The longer leg always goes in the rectangular pad in M4TM projects.

Be careful to put the LEDs in the correct side of the board. You'll be putting them in the side with the little LED symbol, NOT the side that says "cut flush"

The LEDs that go under the potentiometers should go all the way through so the lens parts stick up.

The LEDs that go under the jacks can't go in that far because the plug would hit them.

Solder the LEDs in from the "wrong" side, the side that the component is on. We do this so that when we cut the LED legs flush we still have a reliable electrical connection.

Now it's time to cut those LED legs flush, flush, as flush as possible!! If there's even half a millimeter raised area here it can make contact with parts of the Thonkiconn jack when you're plugging/unplugging things. So cut them flush, my guy.

It's time to install the rotary encoder! Put one nut on it before going too far

Install BUT DON'T SOLDER the Thonkiconn jacks.

Also install (and solder) the bottom 100K potentiometer. **ALERT** snip the metal locator tab off of the potentiometer if there is one. Maybe there isn't one, and that's okay.

Next, put the panel over the project, press the panel against the nut on the rotary encoder and see if the panel is also pushing down the "clear hat" pushbutton. If it is, adjust the nut so that with the 2nd nut installed, the pushbutton isn't permanently held down. When everything's adjusted correctly, you can use a droplet of superglue or any other glue to keep the bottom nut in place (not the top nut)

When you're happy with the panel placement, install all the nuts for the jacks, the potentiometer, and the rotary encoder, and solder all those parts in place.

Then? Take the faceplate off again because it's time for the trimmers and Eurorack header YAY!!!!

Here's the Eurorack header and the box trimmers installed. That's all. You could do this earlier if you wanna go back in time.

*Okay at some point* I installed the tall tactile pushbuttons in place. I forgot to take a picture of that? It should be done with the panel in place so they can poke through the holes like they need to do. Whoops.

Toss the JuanitoPots where they go. If you don't have any JuanitoPots, you can use any potentiometer that you can get working with the footprint. If you use cheap plastic pots or "tall trimmer" pots, the mechanical legs will be too wide -- snip them narrower or mangle them somehow if you want, it'll be okay, as long as they're held securely. But if you don't have JuanitoPots, the light won't shine through which is an enormous bummer

First, remove all four of the pins in the OLED screen. Clear the solder from the holes if you want, but you don't have to.

Try not to damage the OLED PCB while doing this. I do it by heating the pin up fairly hot with the soldering iron, and pushing them one-by-one down while pulling the other side with pliers.

First? A note about these little screens.

They are CHEAP to buy and CHEAPLY manufactured. The screen part is never perfectly aligned with the PCB part. They don't even have a standard pinout or hole pattern. So when building with these, we need to be ready to be somewhat flexible.

SO!!! Take some thin solid copper wire, bend some lengths in half, attach the loop part of the wire to the mounting holes in the OLED PCB, and solder them in place. It is Not important to have them exactly right -- the reason we're using wire like this is that it's possible to bend it around and have it still work.

Get all four mounting holes set up with whiskers of copper wire.

Now it's time to take the protective film off the OLED, and stare intensely at it, trying to see the subtle difference in the area that shows the image. LOOK AT IT!!!! It will be slightly lighter and a bluish color. That rectangle of display area is what we need showing through the window in the front panel. When you're positive you like the orientation and squareness of the display relative to the panel, tape the OLED to the panel.

Be aware that the OLED screen is a fingerprint magnet, and taking the protective film off is important to be able to see the display area... so be careful in this step not to smudge the screen with your fingers or tape adhesive. It's not a huge deal, you *can* clean the screen but you want your minty fresh module to be minty fresh.

It's fiddly, but get the corner wires of the OLED need to go through the pairs of holes on the module's PCB. Notice the OTHER pairs of holes right at the PCB corner? Don't mess with those yet.

Get the front panel positioned where it needs to be over the jacks and pots and whatnot. It's a good idea to install the 2nd nut on the rotary encoder just to hold the front panel exactly where it needs to be.

Solder the pairs of wires, snip them off, remove the tape holding the OLED to the front panel, and take the panel off! Look! A securely-mounted, properly aligned OLED screen!

It's time to connect the electrical parts of the OLED to the PCB.

The two data lines are standard across all these parts. Put a leftover pin (or wire) through the project PCB, and press the end of it against the corresponding hole in the OLED, heat up the pad on the OLED with your soldering iron, and it'll pop into place. Solder the pin (or wire) to the project PCB, and then touch up the pad on the OLED to make sure it's nice and solid.

The G and V+ connections are NOT standard, so there's two pairs of pads on the project PCB for you to use. It's important to get it right so you don't break the screen. I haven't been able to use solid pins for these connections in my builds -- they're too solid and thick. But a length of wire (or resistor lead or whatever) will work just as well.

The top half of the Etch is only held together by the rotary encoder nut, and that part, and the tactile switches to each side, get pressed often, which will put stress on the front panel. Which? has a giant window cutout.

So it's a good idea to bend some copper wire to affix the top of the front panel to the PCB. This makes the module semi-permanently assembled -- you'll need a soldering iron to take the front panel off. Or you can just snip the wires and get new ones, whatever. But this step does make the module more sturdy.

The module is assembled! It's time to adjust the two trimpots on the back of the module. First the top one, labelled input trim.

First, connect your module to power. If it turns on, do a short happy-dance. Turn the encoder to "calibration mode" and click it. Use a patch cable to connect the output to the input. Turn the attenuator next to the input all the way up. Then, adjust the trimpot according to the instructions on the screen.

The other trimpot labelled Output Trim can be adjusted so that the output voltage is exactly one volt per octave. Get out of calibration mode by pressing the encoder, and select Quantizer Mode. Connect the Etch output to a 1V/octave VCO. Connect a slow-moving LFO to the input, listen to the results from the VCO, selecting your choice of scales with the rotary encoder, and adjusting the three JuanitoPots as you see fit. Adjust the trimpot until you're happy with the in-tune pitch coming from the VCO.

More information about the quantizer mode is over here. Especially fascinating (and confusing to me) is the weighted scales. Play around with it!! Enjoy!!!