This week's objective was to measure something by adding a sensor to our microcontroller board. I decided to make my board more future proof for weeks to come. For the next two weeks or so, I want to make a sound reactive led cloud. Using a microphone, I can listen to music around and make the leds pulse and change color to the beat. To accomplish this, I decided to make a SAMD21E main board with a bunch of headers connected to all the pins. I'm also making a breakout board for the sensor I'm using this week - a microphone.

The Main Board

I started this week off by making the main board first. Since I wanted to use a microphone, the SAMD21E was the best board for me. Luckily, I used a SAMD21E in a previous week so I was able to copy what I had from a previous week to use as the basis.

The first things I added was 5 2x2 headers to break out all the unused pins on the SAMD21E. Then I added 3 headers to create extra pins for power and ground for breakout boards. I added one 2x2 header for 3.3V, one for 5V, and one for GND. To make things simpler during routing, I replaced the 2x5 used for programming the board with a 2x2 header. Then that was mostly it for the schematic.

The routing was the hardest part of designing this board. It was much bigger than previous weeks and I wanted to challenge myself by using the least amount of jumps possible. Overall, I had to add 3 more jumps to accomodate all the parts and route them all. I had 16 mil width routes in my board but that produced a ton of errors for routing to the SAMD21E board. This was because the pins were all very close to each other. So I had to change the route width to 12 mil for all routes out of the SAMD21E. Anthony showed me a really cool hack to changingroute widths super fast. You click on the wrench in the upper right hand corner and then click on width in the drop down. Then click whatever mil width you want. After that, you can click any route and it will automatically change the width to the chosen one.

The Breakout Board

My sensor for this was a microphone so I decided to use the CMM-4030D-261-I2S-TR Mems Microphone for this week. To integrate it, I made a small breakout board for it in Eagle/Fusion. The board was very simple. It has 2 2x2 headers to connect the relevant pins on the mic to the main MCU. I also added a pull down resitor and two capacitors as specified in the datasheet.

Manufacturing

Once I was down routing the main board I was able to mill it. I chose to do it on the Roland because the Othermill was occupied.

Using the Roland

To use the Roland I needed two things: an image of the outline of the board and an image of the traces on the board. To do that I went through all the display layers (a pull out menu on the left) and toggle which ones can be seen. For the outline image, I kept only the Dimension layer and hid every other layer. Then I typed "export" into the command line, clicked the monochrome option, and click the window option for where to capture the image. Make sure not to move the board and do the same for the traces. For the layers, keep only the "Top" layer and hide everything else.

After I had the images, I had to modify them to get them ready for the Roland. I used Gimp to do the image editing. I also got an amazing amount of support from Alec who was EDS staff at the time. I used the bucket tool to fill in the area inside the outline image with white, resized the canvas, and centered the board. I used the same numbers for centering and resizing for the traces. This is very important because the Roland needs to start in the same area for both parts.

Once I had the final images, I uploaded them to the software controlling the Roland. I first milled my big main board so I started with uploading the traces for that. I adjusted the settings for the Roland to mill the board at the right x and y. Then I moved the endmill all the way up into the mill mouth (or whatever it is called), moved the mill head as close as possible to the bed without breaking the bit, and then loosened the mill head to allow the tool end to reach the bed and tighten it there. Then I clicked a bunch of buttons and started milling. Once the traces were milled, I switched out the bit to a 1/32nd inch bit and repeated the same steps with it for milling the outline.

Soldering

Soldering the main board wasn't too hard. The most difficult part was soldering the MCU but using a microscope made it much easier to do. I chose to first solder the MCU and then all the small parts like the resistors, voltage regulator, capacitors, and leds. Then I soldered all the headers. They were clunky and quite difficult to solder.

For the breakout board, it was a lot harder of a time to solder. The mic had no legs so I had to get a lot of help soldering it from Alec. The method

It Works!