Week 06: Electronics Design¶

Motor Driving Board¶

Motor driving board — Designed an electronics board for my potential final project, featuring two dual H-bridge drivers for stepper motor control.

Assignments¶

Group assignment:¶

Use the test equipment in your lab to observe the operation of a microcontroller circuit board (as a minimum, you should demonstrate the use of a logic analyzer)
Document your work on the group work page and reflect on what you learned on your individual page

Individual assignment:¶

Use an EDA tool to design a development board that uses parts from the inventory to interact and communicate with an embedded microcontroller

1. Group Assignment¶

We analyzed the QPAD board running the FabDino game using a digital oscilloscope. We observed the I2C signals — both SCL and SDA — and discovered a mismatch between the pull-up resistance and the I2C frequency configured in software. The waveforms showed ringing and slow rise times as a result. By adjusting the software settings to better match the hardware, we obtained significantly cleaner waveforms.

FabLab Kannai group work page

This exercise was a valuable reminder that hardware and software must be designed in concert. An oscilloscope is an excellent tool for diagnosing exactly this kind of interface mismatch — something that would be very difficult to identify from code inspection alone.

2. Individual Assignment — Electronics Design¶

2-0. Simulation on Wokwi¶

Before moving to schematic capture, I wanted to simulate my circuit to validate the concept. My goal was to prototype the electronics for my final project — a drawing robot that uses stepper motors and a servo. However, Wokwi’s component library does not include the specific H-bridge drivers I planned to use, so a full simulation was not feasible.

Instead, I used Wokwi to simulate the QPAD Dino game as a way to familiarise myself with the tool and practice simulation-driven development.

Wokwi simulation

2-1. Schematic¶

With the concept validated at a high level, I moved on to designing the schematic in Fusion Electronics (Autodesk Fusion 360’s integrated EDA environment). Note: the Fab component library was not functional during this session, so I worked with the standard component libraries available.

The board is designed around the Seeed Studio XIAO RP2040 as the main microcontroller. The design goals were:

Drive two stepper motors — one for each axis of the drawing robot
Control a servo motor for raising and lowering the pen
Expose an I2C port for a camera or other sensors

To drive the stepper motors, I used two DRV8421 dual H-bridge ICs. Each DRV8421 provides one full H-bridge per channel, allowing precise bipolar stepper motor control from a compact footprint.

Schematic

2-2. PCB Layout¶

After completing the schematic, I routed the PCB in Fusion Electronics. The layout prioritises keeping the motor driver circuitry close to the power connectors to minimise trace inductance on the high-current paths, while keeping the XIAO and I2C signals away from the switching noise of the drivers.

PCB layout

Checklist¶

[x] Linked to the group assignment page
[x] Documented what you have learned in electronics design
[x] Checked your board can be fabricated
[x] Explained problems and how you fixed them.
[x] Included original design files (Eagle, KiCad, etc.)
[x] Included a ‘hero shot’

Digital Files¶

Fusion Electronics board file