this week's group assignment was to probe an input device's analog levels and digital signals.

Since I had a problem uploading the AccelStepper library to SAMD11 due to small memory, I started this week by making a new development board with SAMD21.

I used SAMD21E17A. As always I started the process by looking at the datasheet, and pinout. As references, I used SAMD21E17/E18 devkit board by Quentin Bolsee, SAMD21E piano and synthesizer by Quentin Bolsee, and Neil’s example from Week6 embedded programming,

As a design concept, I wanted my PCB to have a capacitive touch function and maximum pins out for external connection.

At first, I thought anypin works with capacitive touch but then my classmate told me that only specific pins have the capability. After researching it, I found out that it is explained in the SAMD21 datasheet in the Peripheral Touch Controller (PTC) section. PTC pins are shown in the table of I/O Multiplexing and Considerations. If a pin has X or Y in the PTC column, it should work with capacitive touch.

Later, I also found out which pin should be connected to DIO and CLK by looking at the table of I/O Multiplexing and Considerations.

After milling the PCB I found out that the footprint for SAMD21 pins are too close to each other and they were merged. To fix this problem I needed to go back to KiCAD and fix the thickness only for those footprints. I followed the steps below.

1. Shift+LeftClick - select a pin
2. E - to edit
3. Change Pad size Y to 0.4mm
4. RightClick - Copy Pad Properties to Default
5. Select pins that are the same orientation
6. RightClick - Paste Default Pad Properties to Selected
7. Repeat the process for those in another orientation

After milling the PCB and soldering components on it, I flashed SAMD21 with the same workflow I did in Week 8 Embedded Programming

However, after burning the bootloader, my PCB was not recognized as USB. So I did basic troubleshooting such as checking connecting on PCB, connecting different USB ports, and checking my PC setup. Later my tutor found out that I had pins for D+ and D- flipped. I should have checked the table of I/O Multiplexing and Considerations. On the table, it shows USB/DM (D-) and USB/DP (D+).

To fix this problem, my tutor recommended I simply swap connecting by using a wire. This solution fixed the problem and the PCB worked perfectly, however, I made new SMAD21 PCB later because the wire connection is very weak.

Because the previous SAMD21 PCB had was a frankenstein I wanted to make new one. This time I made it with out capacitive touch because my tutor told me that having capacitive touch in the middle when the pins are connected to device, it might create more noise. This time I use almost all the pins and made the PCB little more compact.

I found a problem when checking the traces it was getting unexpected value for voltage. Later my tutor found out that I had 2 different GND which are not connected to each other. So I used a extra wire to fix it.

Files
SAMD21_02.kicad_pro
SAMD21_02.kicad_sch
SAMD21_02.kicad_pcb
SAMD21_02-F_Cu.svg
outline02.png
trace02.png
outline02.png.rml
trace02.png.rml

For this week's assignment, I wanted to try using potentiometers to control stepper motors like a DJ.

First I checked with my tutor and he showed me potentiometers that are available in the lab. After that, I decided that I wanted to play with a rotational potentiometer and a sliding potentiometer. So I grabbed them and checked their condition because some of them were dusty and there was a chance that they might not work properly.

To check the condition, there are usually 3 pins coming out from the potentiometer, connect a power supply to the ones on the sides (usually GND & VDD) 0and connect the middle one (usually for reading voltage) to a multimeter. For the rotational potentiometer, I opened a new package and for the sliding potentiometer all of them in the lab was not working properly so I ended up buying at Charles Servei de Components Electrònics

Because I could not find a symbol and footprint library on KiCAD for these analogue potentiometers, my tutor advised me to make them by myself. I measured all the necessary dimensions and followed this YouTube video How to design custom Footprints & Symbols in Kicad

The workflow is not too hard and I am actually glad to know how to do this. After that, I designed my PCB and milled it. I needed to be careful with the side of the PCB because the potentiometer will be installed from the back and it will be soldered on the front side. Also when this is in use the back side will be facing up, so I needed to get my head around the flipped design of this PCB.

After all, my DJ set-looking PCB is made. Something to remember, when I made foot print for holes I used tolerance around 0.1~0.2mm which was a perfect fit. But I could have made the footprint around the holes bigger to make it easier to solder.

Then I moved on to the next step. I simply combined the Step Without Delay code with the code that moves the motor according to the Potentiometer. As a result of this, I was able to change the speed of the motors with the potentiometer without delay.

Lastly, I applied the previous code to 3 motors. To do this I needed to have three counting and interval separately so I added 2 more of the Step Without code. As a result, I was able to move multiple motors with different speeds for each of them.