9. Embedded programming

This week, the randomizer chose me. Neil mentioned that Mods can increase the spaces between traces by alternating bits or something. Note to investigate.

Neil's page for this week's topic

Group project

Calibrate the milling machine

NB.Only fasten the bit on one side (the side with black tape).

1. Unfasten the bit -- where the black tape is
2. Raise the bit into the collet to make space to get the tool close enough to the bed without touching
3. Fasten
4. Lower the tool using the Z-down button on the MDX
5. Unfasten and make sure the bit is touching the bed
6. Fasten
7. Check to make sure that you can't slide a piece of paper underneath the tip of the bit

Also, make sure to check the z-axis mill height at different points along the surface of the copper plating. To move the mill around the milling bed, change the X and Y values of the origin settings (in Mods) and select move to origin to move the bit there.

NB. Remember your original origin settings.

When you want to check in on how a mill is going, push the view button on the MRX. The milling will pause and the bed will move forward. Push view again to send the bed back.

If, at any stage, there's an issue with the machine and a mill needs to be started again:

• Press the view button (to pause the job)
• Unplug the MDX at the computer's USB port
• Hold the Z-up and Z-down buttons for ten seconds -- this resets the machine
• Reconnect the MDX to mods
• Move bit back to origin

Because of the tiny scale we're working with, the mill isn't always at the right depth. There are a few tricks to making tweaks to get this right. One of them is that when setting the z-level, apply a bit of pressure on the board while the bit is still unfastened, while compressing, tighten the bit fastener.

Solving for z-level issues can also be done by changing the cutdepth in Mods, or by unscrewing the bed, placing a piece of paper down, and screwing the bed back on (this is the preferred method).

Mods

For this week we learned how to mill and cut our own PCBs.

First the F.Cu layer (the first copper layer).

Open Mods > programs > open program > Roland - MDX mill - PCB

Connect the computer and the machine (this setting is on the far bottom right of the screen).

Choose the USB-Serial Controller D option.

select png file -- Make sure that the F.Cu and Edge.Cuts are the same size (by checking the dimensions)

Define the milling bit. We use a ball nosed .25 mm tapered bit. Below are the settings that we used.

Mill raster 2D. Set the tool diameter, cut depth, max depth, offset number, and offset stepover. The settings I used are listed in my Individual project section below. When setting up the tool diameter settings, always use a 0 before the decimal place; ie 0.00.

Click Calculate.

If everything works properly, a tab should open with a render of the 3D toolpath.

Move the bit to the origin (NB. Make sure to write down/save the origin).

Web serial > send file will start the milling process.

Before milling, make sure the z-axis is calibrated.

After the F.Cu is milled, then comes the Edge.Cuts layer.

You do not need to restart the machine after a completed job, only when a job is aborted.

• Move mill to origin
• Select Edge.Cuts png
• Keep milling bit settings
• Change max depth in the mill raster 2D settings
• Click Calculate
• Send file

Despite what it shows below, when milling my individual project, Henk suggested that I use a cut depth of 0.2mm.

View toolpath in the view toolpath box, to the right of the mill raster 2d box.

Important settings

• F.Cu settings

offset = 0 (so that it mills everything, and not just the outline)

• Edge.Cuts settings

offset = 1 cut depth = 0.2 max depth = 1.55

KiCad export

With the latest KiCad update to version 9, the export / import to Mods is broken. The work around is to upload Gerber files to the Gerber to image tool made by Fab Academy's Quentin. Below are the steps on how to do that:

• Start by importing the F.Cu .gbr file (one at a time) to Quentin's tool
• Select Black and white (the machine will mill the white)
• Make sure to lock the dimensions (look for the lock icon)
• Download render
• Follow the same steps with the Edge.Cuts
• But this time select Fill edge cut AND Black and white
• Download render
• The PNG files can now be imported to MODS

Make sure to lock the dimensions.

Henk PCB redesign

Making the outline (Edge.Cuts layer)

This is how you make line traces in Inkscape:

Bitmap > brightness cutoff dialed up until the object is filled in

Stroke > Fill tab > `No paint` > Stroke paint tab > `Flat color` > Stroke style tab > adjust width

Figuring out what size the outline should be required a bit of back and forth. The outline didn't need to be any exact size, so I tried two or three different measurements until one suited the existing components.

Making bitmap Henk for F.Cu

I had to re-lay my traces so that they would sit nicely with the bitmap Henk F.Cu layer. Based on the recommendations of a previous student, I decided to use 0.4mm for pin traces and 0.8mm for power traces.

Then I imported the same Henk image into Inkscape and used the Bitmapping tool to get a single color trace of Henk. I did this in the same document that I had created the outline in so that there would be a reference to work with.

I then imported the bitmap Henk SVG into KiCad's PCB editor and further adjusted my circuit design around it.

I placed the phototransistor in the eye of Henk, as it would have a copper/ground connection.

Adjusting the F.Cu Henk

I used Inkscape to arrange the traces of my PCB so that they would align over the F.Cu layer I was making of Henk.

• Export the gerber file of just the traces and components from the circuit design
• Use Quentin's tool to convert that into a PNG
• Make sure to download the PNG so that the traces are white
• Open the Inkscape file of Henk and the outline
• Add the circuit design PNG over Henk's bitmap image
• Export as a PNG (DPI = 1500)
• Open the new PNG and use the bitmap function to trace it
• Export the traced layer as an SVG
• Import that into the your PCB editor project (shift+cmd+f)
• Layer > F.Cu
• IF your bitmap is super complicated, make sure to keep Group imported items selected

Export the Gerber file of the traces and pads, convert it to PNG, add it on top of the Inkscape file:

Remove the areas where the traces and pads are by "blanking" them out:

Export the "blanked out" image as a PNG > open it in a new Inkscape file > create a bitmap layer > export that as an SVG

Make sure to create zone fills and edit them with the keep out function it's much easier to deal with copper layers that will be over / around traces.

NB. Make sure to Draw filled zones (option + z) and fill them (b) before importing the image bitmap Henk F.Cu layer.

Import the SVG file into the KiCad PCB editor.

Just a note: In the future, instead of trying to clear individual paths, I would clear out a big space, if possible, and fill that space with zone fills in the PCB editor. KiCad does a much better job of making space around traces than I could (sounds obvious, I know). Below you can see why:

This is the file that I sent to Mods for the F.Cu layer:

Image dimension problem

This section is mostly to highlight the issues I had and ways to avoid them.

One of the major issues I had was the F.Cu and Edge.cuts layers didn't fit together. That's because the PNG files were different dimensions. They should be the same dimensions. I do have this in my notes above, but I forgot. The PCB mill still worked, it was just a bit of a mess.

Luckily, I totally destroyed my first PCB attempt with some bad soldering, that meant I had a second chance at getting my dimensions right.

There are lots of places where my image sizes could have gone out of wrong. During my second print, I noticed that in Inkscape I had sometimes exported the dimensions of a specific layer rather than of the border of the project. That happens when you click on the layer right before exporting. You need to either deselect the layer or select the project's boundary before exporting.

Also, I hadn't made sure to lock the dimension settings on the Gerber2PNG tool. I mentioned that before, but it's a tricky lil one that might slip past.

On the second attempt at milling I had a smaller copper board. In Inkscape, I set the project dimensions to a few milimeters smaller than the board size and made sure to have the right dimensions selected during the export.

This is the result:

Soldering

For soldering we used the .5mm solder wire.

It's important to make sure to clean the tip of the iron with the flaky copper / wet sponge by the soldering desk.

Pre tinning a surface is when you press the tip to a surface and then let solder flow onto it. Typically this is done before attaching a component. I misunderstood how this process works and I pre-tinned multiple surfaces for a multi-pinned component. This is a no-no as the solder will cool and create an uneven surface, making it difficult to put the compnents one flat.

Common soldering mistakes

Soldering tips

My first soldering attempt was to add extender pins to my ESP32. Some of the pin extenders weren't soldered properly on and so I had to add more. To do that, add a bit of solder to the tip and then press into existing solder and onto the pad.

If solder needs to be removed, heat it up and use the suckgun. Remove as much as possible. Before soldering on the component, heat the leftover solder and put the component on it (Henk even used the tip to move the solder around the pad).

NB. Make sure to wash the pcb with soap and then rinse with water, before soldering.

I was struggling to ascertain from the data sheet which side was the cathode of the LED (negative / ground facing side). For that, Henk recommended using a multimeter, so here's a video how to do that.

The next section of my soldering journey could be called "Don't Tell Henk."

When soldering on my extender pins, I took out the ESP32, so that I could solder the pads that were underneath the MCU, but when I did that it yanked off some copper. Luckily the trace that was most damaged wasn't being used. The other one, I soldered over and it seems to work fine.

Next, in this section of things I did wrong/right, is that the PCB had two traces connected that shouldn't have been. I used a knife and another sharp object to create some spacing. This is how it turned out:

Digital files

• Henkduino F.Cu & Edge.cuts images + gerber files