Week 7: Embedded Programming

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Week 7: Embedded Programming

Read microcontroller datasheet.
Program board to do something.

The final board I fabricated in week 5, incorporated a D11D microcontroller, and is shown in the image below. I did not read the D11D's 981 page datasheet in its entirety, but instead focused on the following sections: pinout, block diagram, memory, power supply, internal clock, electrical characteristics, packaging information, ports, and analog-to-digital convertor. I will discuss findings and comparisons with other microcontrollers in the group assignment section. While reading the datasheet, I often found myself searching on the Internet for more layman component descriptions. Prior to this week it was difficult for me to fathom how the capabilities of a microcontroller fit in such a small package, and after learning more about the D11D I am even more astonished.

The group assignment this week entailed comparing the performance and development workflows of various microcontrollers. However, prior to diving into this assignment, I wanted to better understand the difference between digital and analog pins on the microcontroller. Both pin types can act as inputs or outputs for the microcontroller, but their capabilities differ greatly. A digital pin only has two positions (e.g., ON or OFF, HIGH or LOW, 0 or 1, etc.). Controlling the ON/OFF of an LED can effectively be done with a digital pin. An analog pin can have an array of positions with fine or coarse increments that can be scaled to the desire of the user. For example, an analog pin can be used to control motor speed. It is my understanding that through code, one can adjust the duty cycle of a digital output (e.g., square wave ON period duration) to simulate an analog signal. I look forward to experimenting with this in the coming weeks.

Everyone in the EECS section used either the SAM D11C or the SAM D11D this week. Beyond the obvious differences of pin count and package size, there are more similarities than difference between the SAM D11C, D11D (20 pin), and D11D (24 pin). The below table outlines some of the similarities and differences.

My primary takeaway from this comparison is that increasing to a larger SAM D11 microcontroller offers more converters and interfaces, but you are still operating with the same programming architecture and kilobytes of memory. The ARM Cortex-M0+ core has two 32-bit bus interfaces. One is an AMBA-3 AHB-Lite interface that connects to peripherals and system memory. The other is an Input/Output port interface.

Previously to this course, my programming experience was extremely limited. I was briefly introduced to the enterprise of Arduino during a previous course, so I elected to use Arduino's IDE application which I already had installed on my computer. Working in Arduino's IDE I developed code using programming language "C". The three simple codes that I developed to demonstrate the programmability of my board are presented in the following subsections.

The first code I developed was to make the LED on my board blink at a set frequency. In the code shown to the left, I set the LED to an ON duration of 1 sec, followed by an OFF duration of 1 sec. Using an oscilloscope to probe the pin output to the LED, I was able to observe that the LED was in fact cycling ON/OFF once every two seconds. The below image shows the oscilloscope screen while the LED was cycling.

The second code I developed was to control the ON/OFF of the LED with a button. I was aware that my button was contacted to an analog pin of the microcontroller, but since the button is either ON or OFF, I used the "digitalRead" command instead of the "analogRead" command in my code. Again, I used an oscilloscope, this time to observe the button bounce that Anthony demonstrated during week 5. I added a 50 ms delay between the ‘if’ statements of the void loop to eliminate the initial button bounce.

The final code I developed was designed to test my final project prototype shown in the below image. Using the MOSFETs on my board and a DC power supply, I created a code that cycles current to wire coil pairs around my induction machine. Sadly, the magnetic field induced by the current carrying coils was not strong enough to create rotation of the rotor. Using the Hall Effect sensor shown below I attempted to increase the induced magnetic field by decreasing the distant between wire coils and the permanent magnetics affixed to the rotor and by adding iron cores to the coils. These alternates doubled the magnetic field strength, but was still not sufficient for inducing rotation in the rotor. I was able to use an oscilloscope to confirm that the MOSFETs were cycling OPEN/CLOSED as anticipated. To have success with my final project I will have to refine my design to increase magnetic field strength.

This is the Hall Effect sensor I used to measure the magnetic field induced by my wire coils.

This is the prototype I developed for testing my final project design; glad I made a prototype, because it looks like I have some significant changes to make.

Known your pins, an analog pin can be used for digital input, but a digital pin cannot be used for analog input.
Code commenting is essential, especially if you want others to understand it.
The testing and evaluation of a prototype is vital in producing a successful final design.