Component Selection

Final Component Selection Table

Component	Component Datasheet	Price
PIC18F27Q10-I/SO (PIC)	Link to Product	$1.45
DRV8889QPWPRQ1 (Motor Driver)	Link to Product	$4.17
35BYHJ30-36A (Stepper Motor)	Link to Product	$2.65
LM2575-3.3WU (Voltage Regulator)	Link to Product	$1.75
L6R24-120 (Power Supply)	Link to Product	$8.95

Final Decision Making Process

My goal for my decision-making process was to find components that were compatible with each other and had longevity. For my 3.3V Switching Regulator, I chose the SMD variant of the one used in previous labs. I was familiar with its circuitry, almost guaranteeing a working switching regulator when testing the prototype. My PIC choice was also inspired by the one used in class, as it features the same program memory and RAM size as the DIP given in class. On the other hand, both the motor driver and motor were chosen due to their affordability while also having to rely heavily on their datasheets. This allowed me to meet my product requirements, utilizing a PIC microcontroller, a 3.3V switching regulator, an SPI motor driver, and a stepper motor. I also chose a power supply with enough current to supply my needs for the entire subsystem.

Role and Responsibilities

I am responsible for the actuator and using a PIC. This will be done using a stepper motor to control the rotational movement of the solar panel so it can face the sun. I will communicate using a Serial Protocol Interface (SPI) along with a stepper motor driver. To communicate with the daisy chain, I will communicate over UART to receive data from the optical sensor, allowing the stepper motor to rotate based on where the sun is facing. The microcontroller will be powered using a 3.3V switching buck regulator and a 12V power supply to power the 12V stepper motor.

MCC Configuration

I chose a 28 pin PIC as my main microcontroller as my subsystem will initially only need about 6 pins to work effectively. Two pins are designated to RX and TX pins so I can communicate to the daisy chain network. 4 pins are designated to the stepper motor driver, focusing on SCK, SDI, SDO, and SS. We have a clock, serial input, serial output, and slave select that will connect to the stepper motor driver. Other pins are free of use and can be used for debugging purposes. RA0, RA1, and RB5 are used as debugging LEDs and push buttons. RA2-RA3 are used to power up the motor driver's nSLEEP and DRVoff pins which are needed based off the DRV8889 datasheet. RA4-RA5 were used as debugging header pins and testing. RB0 acts a digital output pin to enable and disable chip select.

PIC Rationale

ESP Info	Answer	Help
Model	PIC18F27Q10-I/SO	Include the entire part number (leave off any letters at the end that specify the package type)
Product Page URL	Product	Do not paste links directly into the table. Use a link
Datasheet URL(s)	Datasheet	Do not paste links directly into the table. Use a link
Application Notes URL(s)	Applications	Do not paste links directly into the table. Use a link
Vendor link	Vendor	Digikey, Jameco, etc. Do not paste links directly into the table. Use a link
Code Examples	N/A	url(s) for libraries on github or other sites related to the microcontroller and your planned peripherals
External Resources URL(s)	External Resources	Search on Google and YouTube for other resources for each specific microcontroller.
Unit cost	$0.84	Find in the Microchip online store, or Digikey
Absolute Maximum Current for entire IC	350 mA	Find in the microcontroller datasheet
Supply Voltage Range	2.3V-5.5V	Min / Nominal / Max / Absolute Max, as found in datasheet
Absolute Maximum current (for entire IC)	250 mA	as found in datasheet
Maximum GPIO current (per pin)	50 mA	as found in datasheet
Supports External Interrupts?	Yes	as found in datasheet
Required Programming Hardware, Cost, URL	MPXlabs, Snap Programmer	found on the microcontroller's product page
Works with MPLabX?	Yes	Required. See Microchip Development Tools
Works with Microchip Code Configurator?	Yes	Can be validated in MPLabX. Screenshot required.

Module	# Available	Needed	Associated Pins (or * for any)
GPIO	23	8	RA0-RA5, RB5, RB0
ADC	23	0	*
UART	4	2	RC6-RC7
SPI	8	3	RB1-RB3
I2C	4	0	*
PWM	23	0	*
ICSP	1	1	RE3
...	...	...	...

Major Components Selection

PIC Microcontroller

PIC16F1503-I/SL
$0.99
Link to Product

Pros	Cons
Fast Shipping	Can't communicate over UART
Small for its capabilities	Has only 14 pins

PIC18F27Q10-I/SO
$1.45
Link to Product

Pros	Cons
Has UART and SPI compatibility	Small programming size (28kB) compared to 128 kB used in class
Functions with MPX labs	Bigger compared to other options

PIC18F14Q20T-I/SS
$1.06
Link to Product

Pros	Cons
UART and SPI compatibility	Compatibility issues
Possibly easier to solder	Has only 14 pins

Choice: Option 2 PIC18F27Q10-I/SO

Rationale: I chose this specific microcontroller because it can communicate with UART and use an SPI to effectively control my stepper motor driver. It also has the necessary pins for the entire subsystem, leaving out extra pins for debugging purposes. It also works with MPX labs and the snap programmer. It also needs around 2.3V -5.5V to power which works perfectly with the switching regulator. The max current for GPIO pins are 50 mA and about 250 mA for the entire package. A 24kB programming memory should also get the job done.

Motor Driver

DRV8434SRGER
$3.13
Link to Product

Pros	Cons
Can communicate with SPI	Hard to solder/almost impossible
Cheaper option	Complicated IC factor

DRV8434SPWPR
$3.21
Link to Product

Pros	Cons
Several half bridges	Bigger than other options
Cheaper option	Sensitive Configuration issues

DRV8889QPWPRQ1
$4.17
Link to Product

Pros	Cons
Can communicate with SPI	Expensive option
Stall detection and SPI modes	Only fit for one stepper motor

Choice: Option 3 DRV8889QPWPRQ1

Rationale: I chose option 3 because it is able to support a 12V stepper motor. It is also compatible with my PIC I chose after doing some research. Although it is the most expensive option, it also has good thermal padding and operating temperatures.

Stepper Motor

35BYHJ30-36A
$2.65
Link to Product

Pros	Cons
Cheapest option	7.5 degree step angle
Reliable for testing	Thermal issues

QSH4218-51-10-049
$67.78
Link to Product

Pros	Cons
Bipolar/hybrid	Super expensive
Used on 3D printers	Out of budget

42M100B1B
$37.73
Link to Product

Pros	Cons
Bipolar/hybrid	No datasheet and hard to wire
Decent fit for project scope	expensive with no room for error

Choice: Option 1 35BYHJ30-36A

Rationale: I chose option 1 because it is by far the cheapest out of all the options as stepper motors are really expensive. It also has bipolar capabilities, being able be controlled bidirectionally in response to project constraints.

12V Power Supply

SWI3-5-N-MUB
$4.90
Link to Product

Pros	Cons
Cheapest option	Low current output

QSH4218-51-10-049
$6.75
Link to Product

Pros	Cons
Smallest charging block	Low current output

L6R24-120

$8.95
Link to Product

Pros	Cons
High current potential	Most expensive option

Choice: Option 3 L6R24-120

Rationale: I chose option 3 because it supplies the highest current which will be needed for my stepper motor. I will have extra current in case of power budgetting issues.

3.3V Switching Regulator

TLV61048DBVR
$0.63
Link to Product

Pros	Cons
Cheapest option	6 pin configuration
Supplies high current	No thermal connections

TLV61046ADBVR
$1.09
Link to Product

Pros	Cons
Adjustable regulator	6 pin configuration
Reasonable price	No thermal connection

LM2575-3.3WU
$1.75
Link to Product

Pros	Cons
Buck regulator	Smaller input voltage range
5 pin configuration	Most expensive option

Choice: Option 3 LM2575-3.3WU

Rationale: I decided on option 3 because it has a similar pin configuration as the 3.3V regulator we designed in class. It is also a buck regulator, having a higher efficiency than most regulators. It also can take an input of 12V which is the amount of power coming from the daisy chain network.