RasPi Hat

Remote Labs Supervisor PCB V1.2

NOTE: This project has been continued in a new location, please see: rl-supervisor-two for the latest version of this project

Project Brief - [Remote Labs Supervisor PCB V1.2]

Design a PCB to provide power to remote labs experiments, which involve students programming microcontrollers remotely. PCB should also provide a supervisory role, blocking actuation of experimental hardware if it is likely to cause damage to the equipment.

This allows students to upload their own code to a bare bones microcontroller, without risk of causing hardware damage or unsafe conditions.

Using Remote Labs Supervisor PCB

This document is intended to be a useage guide for the Remote Labs Supervisor PCB, and document the different use cases and configurations it is capable of.

For coded examples of the various features please see PCB Unit Tests, which contains arduino code firmware used during testing all hardware features of the PCB.

For the purposes of this document, it is assumed that the Motherboard PCB is populated with both Arduino Nano IoT 33 Daughterboards (A1 & A2), with shift registers installed, and NOT the bare bones SAMD21 MCU. A seperate document will be provided for cases in which SAMD21 MCUs are mounted to the motherboard directly.

Pin Naming and Shift Registers

All MCU pins will be referenced by the Arduino Pin Numbers in this document. Additional pins are sourced via Shift Registers attached to each MCU. Shift Register pins are labelled as Q0 - Q7. Both MCU connections to their independent shift registers are detailed below.

Complete pinout diagrams for both MCUs and Shift Registers can be found at the bottom of this document

Powering the System

The System should be provided 12v DC power via the yellow XT60 connector J3. The system is specified to draw a maximum of ~ 8A depending on experiment configuration, ensure that power supply selected is sufficient for specific use case.

Diode D6 (Blue) will light to show correct polarity power is provided to input. Diode D7 (Orange) will light to show 3V3 DC power is available to microcontrollers and periferal devices.

Motherboard has reverse polarity protection, however care should be taken to ensure correct orientation of power input. - NOTE: Currently missing protection diode- awaiting delivery

Programming the MCUs

Each MCU, supervisor and student are able to be programmed via the USB connector on the daughterboard, or via UART using the 5 pin headers J26 Student_Prog_Header, and J1 Super_Prog_header.

For UART Programming, a hat is provided for raspi GPIO pins. 5 pin cable should be connected from Raspi hat to UART Programming connector on motherboard.

The USB connectors mounted to the Motherboard should not be used if Arduino Development boards are installed, and are UNTESTED for use with bare bones MCUs installed

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Use Case 1 [Spinner Experiment]

In this configuration the following modules should be mounted to the motherboard:

• Infineon DC Motor Control Shield - A3

In this configuration the following external hardware should be connected as follows:

• DC Motor, wired to the OUTER two pins on J18 DC Motor Output
• Optical Encoder, plugged into J25 Optical Encoder

Using the DC Motor

DC Motor PWM is routed to Infineon DC Motor Controller module via the following logic:

If MOTOR_DIR_A is driven HIGH, PWM is routed from STUDENT_MOTOR_PWM or SUPERVISOR_MOTOR_PWM to MOTOR_OUT_1 If MOTOR_DIR_B is driven HIGH, PWM is routed from STUDENT_MOTOR_PWM or SUPERVISOR_MOTOR_PWM to MOTOR_OUT_2

Care must be taken to avoid driving MOTOR_DIR_A and MOTOR_DIR_B to HIGH at the same time as this will cause shoot through.

In Order to avoid shoot through condition, Student does not have direct input to MOTOR_DIR_A or MOTOR_DIR_B. These outputs are spoofed via the Supervisor MCU.

The MCU able to pass PWM signal to Motor Control Module is selected by MCU_MOTOR_SELECT pin. When HIGH - STUDENT_MOTOR_PWM is active, when LOW - SUPERVISOR_MOTOR_PWM is active.

In order to enable the DC Motor Control Module, OUT_M_ENABLE must also be set HIGH. This is routed from either MCU using the same logic as above, when MCU_MOTOR_SELECT is HIGH, ENABLE is routed from STUDENT_MOTOR_EN, when it is set LOW, ENABLE is routed from SUPERVISOR_MOTOR_EN.

M_I_SENSE_1 and M_I_SENSE_2 output is buffered and distributed to both MCUs.

Supervisor MCU

Supervisor MCU uses the following table for DC Motor Control:

Student MCU

Student MCU uses the following table for DC Motor Control: Note - Student control relys on specific pin configurations of Supervisor MCU

Using the Optical Encoder

Optical encoder signals are buffered and provided to both MCUs simaltaniously, therefore getting useful data from Optical Encoder is the same process for both MCUs

MCUs use the following table for Optical Encoder detection:

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Use Case 2 [Governer Experiment]

In this configuration the following modules should be mounted to the motherboard:

• Infineon DC Motor Control Shield - A3
• DRV8825 Stepper Motor Driver - A4

DC Motor & Optical Encoder are accessed as Use Case 1 above

In this configuration the following external hardware should be connected as follows:

• DC Motor, wired to the OUTER two pins on J18 DC Motor Output
• Stepper Motor, plugged into J19 Stepper Motor Output
• Optical Encoder, plugged into J25 Optical Encoder
• Limit Switch, plugged into J23 limit_switch_A

Using the Stepper Motor

Stepper Motor Driver inputs are routed via the following logic:

When MCU_STEP_SELECT is HIGH, inputs are routed from STUDENT MCU. When MCU_STEP_SELECT is LOW, inputs are routed from SUPERVISOR MCU.

STEPP_EN is driven from Supervisor MCU Only, however does not seem to have any effect on stepper motor function. - Requires further investigation.

STEPPR_FAULT output is buffered and distributed to both MCUs.

LIMIT_1 Limit switch input is buffered and distributed to both MCUs.

Supervisor MCU

Supervisor MCU uses the following table for Stepper Motor Control:

Student MCU

Student MCU uses the following table for Stepper Motor Control: Note - Student control relys on specific pin configurations of Supervisor MCU

Additional Stepper Motor Functions

SW1 - Stepper Mode Dipswitches set number of steps per revolution. If UNPOPULATED setting is at MAX RESOLUTION. (1, 1, 1 ) logic for MODE inputs.

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Use Case 3 [Digger Experiment]

In this configuration the following modules should be mounted to the motherboard:

• Infineon DC Motor Control Shield - A3

DC Motor & Optical Encoder are accessed as Use Case 1 above

In this configuration the following external hardware should be connected as follows:

• DC Motor, wired to the OUTER two pins on J18 DC Motor Output
• Optical Encoder, plugged into J25 Optical Encoder
• Limit Switch, plugged into J23 limit_switch_A
• Servo, plugged into J20 Servo_A

In this use case, supervisor must calibrate and track the position of DC motor to avoid equipment collision with self.

Supervisor MCU

Supervisor has ultimate control of the Servo PPM output.

Supervisor MCU uses the following table for Servo Motor Control:

Student MCU

Student MCU has no direct output to servo_1, instead supervisor must spoof and constrain output; given either a PWM signal, or PPM signal from the Student, applied to Pin A2 of the supervisorU MCU.

Student MCU uses the following table for Servo Motor Control: Note - Student control relys on specific pin configurations of Supervisor MCU

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Use Case 4 [Pendulum Experiment]

NOTE: USE CASE UNTESTED

In this configuration the following modules should be mounted to the motherboard:

• Remote Labs Pendulum PCB Daughterboard - A3

In this configuration the following external hardware should be connected as follows:

• Pendulum Driver, wired to the OUTER two pins on J18 DC Motor Output
• Optical Encoder, plugged into J25 Optical Encoder

Supervisor MCU

Supervisor MCU uses the following table for Pendulum Control:

Student MCU

Student MCU uses the following table for Stepper Motor Control: Note - Student control relys on specific pin configurations of Supervisor MCU

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Additional Features

WS2812 LEDs

To use WS2812 LED strips with any configuration, the following external hardware should be connected as follows:

• WS2821B LED Strip, connected to J24 WS2812B LEDs

Supervisor MCU uses the following table for WS2812B LED Control.

Student MCU uses the following table for WS2812B LED Control.: Note - Student control relys on specific pin configurations of Supervisor MCU

Power Output Connectors

Additional Voltage Bus Connections

Additional headers have been provided for:

• 3V3 DC Power Output (1A Max)
• 5V DC Digital Power Output (2 - 2.5A Max, including USB Socket)
• 5V DC Servo Power Output (1A Max)
• 12V DC Bus (Unregulated - 6A Max)

These are intended for future use, fault finding or reconfirging PCBs to perform tasks outside of the specified use cases.

Thermocouple

Currently Unavailable due to parts shortages

To use Thermocouple Input with any configuration, the following external hardware should be connected as follows:

• K-Type Thermocouple, connected to J22 Thermocouple connector.

Thermocouple input J22 Thermocouple requires IC U19 AD8497 To be populated. (UNTESTED)

Analog voltage is buffered and distributed to both MCUs, Pin A3

Pinout Diagrams

MCU and Shift Register Pinout diagrams

Supervisor MCU

Student MCU

CAD Renders