DIY Stepper Motor Clock with NXP LPC845-BRK

This project is about building a stepper motor clock around the NXP LPC845-BRK board. The design is using a combination of 3D printed and laser cut parts and costs below $15.

Stepper Clock Acrylic Face White Hands

Stepper Clock Acrylic Face White Hands

Below a video of the clock in action:

Material and Tools

The GitHub repository (see links at the end of the article) includes an Excel file with the Bill-Of-Material (BOM). You need

  • NXP MUCXpresso IDE (I have used the V11.0.0)
  • NXP LPC845-BRK board
  • 2 28BYJ-48 5V Stepper Motors with ULN2003 driver
  • 2 Neodymium magnets (e.g. 5x2mm)
  • Realtime clock with battery (DS3231)
  • 2 Bearings 10x15x4mm
  • 2 hall sensors (AH3572)
  • Strand wires
  • 12 M3 nuts and bolts
  • 8 small (2×10 mm) wood
  • Shrink-wrap tubing
  • Soldering station and a few extra wires for power connection
  • Plywood or PMMA/Acrylic material and access to a laser cutter
  • Access to a 3D printer (I used an Ultimaker 2 with white PLA material)
  • Optional: OpenSCAD to change the gears
  • Optional: 3D modelling software to change the 3D models (I used 123Design from AutoDesc)
  • Optional: wireless charging receiver module and charging station (see links at the end of the article for options)

Concept

The clock is designed around the very inexpensive 28BYJ-48 stepper motors (you can get 5 of them including the stepper motor driver board for less than $10).

The idea is to use the two stepper motors to driver each clock hand using a simple gear. the motors are placed in reverse to minimize space. The gears with shaft are 3D printed.

Stepper Motor Clock Concept

Stepper Motor Clock Concept

It is using the 28BYJ-48 5V stepper motors which come with a driver board with a ULN2003 on it:

28BYJ-48 5V with ULN2003

28BYJ-48 5V with ULN2003

Below shows an early prototype using the LPC845-BRK on a breadboard:

Stepper Clock Breadboard prototype

Stepper Clock Breadboard prototype

Gears

The gears are designed with OpenSCAD:

OpenSCAD

OpenSCAD

Using OpenSCAD the design can be parametrized and changed for a different gear factor.

3D printed parts

3D printed parts

3D printed parts

The 3D files are available on GitHub as STL and 123D files:

  • Minute inner shaft and gear
  • Hour outer shaft and gear
  • Minute and Second clock hand
  • 2 stepper motor gears
  • RTC holder
  • Hall sensor holder
  • 4 spacer
  • Microcontroller board holder
  • Small spacer for inner hand gear

The spacer and gear parts should be printed with 100% infill.

To get a zero position, the design uses hall sensors to detect the hand zero position. For this magnets get pressed into both clock hands:

magnets in hands

magnets in hands

Laser Cut Parts

The laser cut parts are designed with Inkscape (.svg):

Laser Cut Parts

Laser Cut Parts

Optionally the parts could be 3D printed too, but this will take much longer. Different materials (plywood, PMMA/Acrylic) could be used, but usually plywood is the least expensive.

5V Motor Power Supply

Because the NXP LPC845-BRK does not expose the 5V on the pin rows, you can get to get it from pin 3 of U3 or from the positive side of C8

VBUS 5V

VBUS 5V (Source: LPC845-BRK Schematics)

Both locations are easily accessible, and I have used it from pin 3 Vin of the XC6206:

GND and 5V for Stepper Motors

GND and 5V for Stepper Motors

Create two pin headers for each motor power supply:

5V Motor Power Supply

5V Motor Power Supply

LPC845-BRK Pin Headers

The board comes with nice and breadboard friendly headers. Because the pins are thinner than normal ones, I recommend using ‘normal’ 2.54mm pin rows instead. Because the K1 switch is placed too close on to the pin row, cut them out so the row can fit on the top side:

Pin Rows

Pin Rows

Wiring

The wiring is pretty simple. If needed, different pins on the microcontroller board could be used (see next section).

GND, magnet sensors and both motor connections are from the left side. Vdd/3.3v and the I2C for the RTC are from the right side:

LPC845-BRK Stepper Clock Pins

LPC845-BRK Stepper Clock Pins (adapted from NXP LPC845-BRK image)

Use shorter wires to connect to the DS3131 (RTC) module:

DS3131 Module

DS3131 Module

  • black: GND
  • red: 3.3V
  • green: SCL
  • yellow: SDA
RTC wiring

RTC wiring

Have the GND and 3.3V wires extended to the hall sensors, or use the extra pin connections on the RTC module. The module gets placed in its holder and attached with a screw below the microcontroller:

RTC Module in Holder

RTC Module in Holder

Solder the two hall sensor (GND, 3.3V and signal) to a cable, isolate with shrink tubing and put them into the holder as shown below:

Assembled Clock Core

Assembled Clock Core

The two stepper motor driver boards get attached on the other side:

Motor Driver Side

Motor Driver Side

Glue/place the small distance holder on the lowerw enclosure:

Inner Shaft distance holder

Inner Shaft distance holder

The bearings get placed in to the lower and top holder plates. The small plywood rings are glued to inside to prevent the bearings to fall inside.

Space for Bearing

Space for Bearing

With the bearing inserted:

Inserted Bearing

Inserted Bearing

Below shows the lower side with the shaft inserted into the bearing:

Lower Side with Inner Shaft and Bearing

Lower Side with Inner Shaft and Bearing

The four distance holders are used to press the top and bottom enclosure parts together. The same time they keep the side walls in place, so there is no glue needed.

Distance Holders

Distance Holders

Below a picture with the top face attached:

Top Face Mounted

Top Face Mounted

Wireless Charging

Instead power the clock with the USB cable, optionally a wireless charging receiver can be placed inside the enclosure. Connect the receiver output to the 5V, e.g. at the stepper motor drive boards.

Wireless Receiver Module

Wireless Receiver Module

Software

The software is written with NXP MCUXpresso IDE and SDK.

Eclipse Project in MCUXpresso IDE

Eclipse Project in MCUXpresso IDE

The project is using the McuLib library which includes FreeRTOS and the hardware high level drivers. The system features a commandline interface using the LPC845-BRK serial port.

Stepper Clock Commandline Interface

Stepper Clock Commandline Interface

The system is running with FreeRTOS:

Stepper Clock Status

Stepper Clock Status

At power-up, the clock moves the hands to the zero position using the hall sensors. Then the hand positions get updated every minute.

Customization

The advantage of laser cutting and 3D printing is that the clock can be customized. Below are a few material and color combinations I tried.

Stepper Clock Acrylic Face White Hands

Stepper Clock Acrylic Face White Hands

Stepper Clock Wood White Hands

Stepper Clock Wood White Hands

Stepper Clock Wood Silver Hands

Stepper Clock Wood Silver Hands

Stepper Clock Wood Black Hands

Stepper Clock Wood Black Hands

StepperClockBlackFaceWhiteHands

StepperClockBlackFaceWhiteHands

I probably build another one with white hands, black face, white face front and everything else in black.

Summary

It took me a while to get the design implmented, with multiple iterations. The clock is workign fine. The gear play could be better, but for a 3D printed one I’m happy with it. The clock nicely shows the time, the stepper motors are silent and working fine. And I think I need to try a few more color combinations.

Happy Clocking 🙂

PS: if you are wondering: this stepper motor clock is just one step (sic!) to a larger stepper motor project 🙂

Links

Advertisements

What do you think?

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.