Stepper blinds driver

Contents

• Overview
• Project Snapshot
• Technical Skills
• Key Design Decisions
• Hardware
• Control Software
• Build Log
• Testing
• What's Next
• Reflection
• Documentation

Overview

Problem

Opening blinds automatically has a range of benefits:

• Easier to wake up in mornings, and aligns circadian rhythm
• Provides more sunlight during day (for an office, this helps improve mood, among other health benefits)

Commercial options have some limitations:

• Can be very expensive
• Almost all commercial devices use geared DC motors, and are very loud when in operation (>50dB)

Goal

1. Low-cost (<$100)
2. Compatible with beaded-chain blinds
3. Near-silent (<40dB)

Features

1. Actuate beaded-chain with positional control (e.g. set to 50%) 2. High precision is not crucial, aside from the start and end positions. However, end position is a mechanical limit (blinds cannot go further than highest position).
2. Controlled via Google Home or Home Assistant for scheduled automations.
3. Device should be compact
4. Powered externally with power supply (extremely clean, minimal, easy to hide cable)
5. Buttons should be minimised for aesthetic 7. Possible structure
   1. Ver. 1 - up/down pushbuttons, power toggle. accessible port for microcontroller. no PCB (wires)
   2. Ver. 2 - power toggle only - small, hidden same-colour micro latch switch. hidden port for microcontroller (possibly a friction fit soft tpu plastic cover for it or similar, like a port cover, same colour). PCB.
6. Easily replaceable components (motor, PCB, microcontroller). highest priority for replicability is the cog/sprocket for the beaded chain which MUST be hot swappable in seconds
7. Custom PCB for final product
8. Clean, minimal box design with all internals hidden, mountable to a wall with standard screws

Project Snapshot

Details

Specifications

Technical Skills

Key Design Decisions

Hardware

Mechanical (Onshape)

The main mechanical component is the mount, featuring two compartments. A thick-walled compartment which is load-bearing and contains the NEMA17, in addition to a thin-walled circuit compartment.

To connect the NEMA17 to the mount, there is a face plate, which also features guides for the beaded-chain to be routed through.

There's also a cosmetic lid which is friction-fit using two pins for alignment and security, hiding the internal circuit while being easy to remove.

The sprocket is parametrically designed based on the following formulas.

The box features hexagonal ventilation holes which balance structural integrity and FDM manufacturability with sufficient surface area for thermal convection to prevent overheating.

Electronics (KiCad)

The electronics involved in this project are for controlling and powering the motor. The ESP32 is the brain, allowing programmed movement logic and eventually communication with Google Home and other smart home systems via Matter over WiFi. The TMC2209 acts as an interface between the ESP32 and the NEMA17, and via the StealthChop2 feature, it allows ultra-quiet motor movement. The MP1584EN is a simple buck converter to step down the 12V from the power supply to the 5V required for the ESP32.

I decided to use a custom PCB because I wanted to make multiple of the device, and eventually open-source it, so I decided inserting components into a PCB would be much easier than wiring spaghetti and frustrating breadboarding. It also gave me a chance to upskill KiCAD and learn about circuit schematics, rule checkers, and the PCB development and manufacturing process.

BOM

Control Software

I wanted to keep this deliberately simple and write it fully myself so I could understand how the stepper control loop works, rather than relying on agentic tools to write something complex that I wouldn't fully understand under the hood.

What it does:

• Serial-based control to move to a pre-defined top and bottom position for the blinds
• Pause command to cancel movement with smooth acceleration.

What it deliberately doesn't do (and why):

• Other features (e.g. Matter over WiFi, auto calibration) have been left out due to time constraints for now and will be developed further in the future.

Walkthrough

• read_int(): Serial user input parser that checks for user commands and accepts valid inputs as commands (0: Stop, 1: Top, 2: Bottom).
• FastAccelStepper Engine: Asynchronously drives the STEP/DIR signal generation using ESP32 hardware timers, allowing smooth acceleration and deceleration ramps in the background.

Build Log

2026-06-30 - Measuring required pull force

• Used a water bucket attached to the blinds to measure the force required to move them.
• At 1.7 kg, the blinds remained stationary. At 1.8 kg, the blinds were able to move.
• The 20 mm NEMA17 was determined to have insufficient torque, leading to the decision to use the 34 mm NEMA17 instead.

2026-07-02 - Initial CAD design

• This design has a removable circuit box area, using dovetail cutouts. It also has removable guides for the beaded chains, secured by M2 screws.

2026-07-05 - Perfboard Assembly

• Image of the components laid out on a perfboard. I've cut the perfboard down to a smaller size for compactness in this image, but for later perfboard iterations I used the full size, just for ease of wiring and troubleshooting (since it was only a prototype, the compactness was evaluated as somewhat irrelevant)

2026-07-07 - PCB Design 1

2026-07-10 - PCB Design 2

• Modified the PCB schematic in KiCAD to flip the footprint of the ESP32C6 by 180 degrees. This ensures that it can be wired correctly while having the USB port point towards the edge of the board, instead of the centre. Code was also updated to reflect the new pins.

2026-07-21 - Control Software Draft

#include <Arduino.h>
#include <FastAccelStepper.h>

constexpr int PIN_EN = 14;
constexpr int PIN_SPREAD = 15;
constexpr int PIN_UART = 18;
constexpr int PIN_STEP = 20;
constexpr int PIN_DIR = 21;

constexpr int SPEED = 500;  // step per sec
constexpr int ACCEL = 1000; // step per sec^2

constexpr int TOP_POSITION = 0;       // steps
constexpr int BOTTOM_POSITION = 1000; // steps

enum user_input
{
  PAUSE,
  TOP,
  BOTTOM,
  OPTIONS_COUNT
};

user_input command = PAUSE;

• Just a basic serial-control script for testing basic functionality (movement up, down, and pausing)

2026-07-24 - CAD Design 2

• This was a major transition. The two-box dovetail architecture was replaced with a single box with two compartments.

2026-07-30 - Motor Testing

• Upon arrival of the board (2026-07-30) and initial basic testing of roller blind movement (a short test program), I determined that the NEMA17 tended to stall quite easily. Upon closer inspection and troubleshooting (including verifying that it did work with a much lighter, smaller roller blind), I determined that the cause was simply insufficient current. The 12V wall adapter I was using only had a rated current of 1A, much less than the planned 3A.
• Order a 12V 3A power supply ASAP, in order to provide sufficient power for the NEMA17 to lift basic blinds.

Testing

What's Next

• The next step is writing the implementation that includes Matter, rather than the basic hard-coded values the script currently uses.
  • For the implementation, I want to keep it buttonless for aesthetics and simplicity of circuitry. So I'm planning to use StallGuard to determine increased resistance at the top of the range of motion (ROM) for calibration, as well as a reduced resistance at the bottom of ROM.

Reflection

I learned a massive amount from this project. On the CAD side, I learned about using variables in my designs, rather than "magic numbers" for dimensions, so everything in my design is fully adjustable via the variables table. I also learned about a lot more Onshape's sketch tools (tangent, normal, and perpendicular constraints), as well as their 3D tools (Featurescripts like Grid Extrude for ventilation, alongside operations like revolve which I used for the sprocket).

I also learned KiCAD from scratch during this project, which was a great learning experience and upskilling opportunity into a new field. Historically I used graphical software like Canva or Illustrator for circuit diagrams, but learning how to write proper, verified schematics was really enjoyable, and seeing my own custom-designed PCB arrive was extremely rewarding. Contrary to what I used to assume about PCBs, it actually saved me time, as I used to have to spend weeks fiddling with breadboards because I didn't take the time to plan my circuit thoroughly. That, combined with the time saved from soldering (only took ~10min to solder the entire PCB!), allowed me to finalise all electronics in about a week.

Documentation

• Firmware Code: /firmware
• Legacy Matter Firmware (v4.1): /firmware/legacy
• Research Log: /docs/research-log
• PCB (Schematic + Gerbers): /hardware/pcb
• CAD Files: /hardware/cad

Acknowledgements & License

gin66/FastAccelStepper: A high speed stepper library for Atmega 168/328p (nano), Atmega32u4, Atmega 2560, ESP32, ESP32S2, ESP32S3, ESP32C3, ESP32C6, Atmel SAM Due, Raspberry pi pico and pico 2

This project is licensed under the MIT License. See the LICENSE file for details.

_{Personal project, July 2026.}