Fixture Switch Reader

Project files for a USB Fixture Switch Reader using a SparkFun Pro Micro and a Ingun FB-ABF-V-I-MA2xxx Inductive Switch.

The Ingun FB-ABF-V-I-MA2xxx Inductive Switch is an inductive sensor which is used to detect when a MA2xxx series manual test fixture is closed.

FixturFab uses these switches to determine when a fixtures has been closed and then automatically start a test run. The switch is powered by 12V, and also has a output of 12V when the fixture is closed.

To interface this to a test system, an SparkFun Pro Micro is used to read the output of the sensor, and then relay that information to the test system over a USB serial port.

Project Structure

The project is split into three main folders:

• firmware
  • Arduino project and sketch for the SparkFun Pro Micro
• hardware
  • Kicad schematic of the prototyped circuit
  • Images of the perf board layout
  • CAD files for the 3D printed enclosure
• software
  • Python module for communicating with the device

Firmware

Arduino 1.8.12 was used to build and program the sketch.

The sketch reads the state of the switch input, sets the status LED, and then processes any available serial commands. The following serial commands are supported:

• version
  • Return device information and firmware version
• read_switch
  • Return the current switch state
  • 0: Fixture Open
  • 1: Fixture Closed

The serial port is setup to use a BAUD rate of 115200.

Hardware

A SparkFun Pro Micro was used to control this project. To build the circuit, perfboard and through-hole components were used.

A Kicad schematic is available for the circuit layout. There are also pictures of the top and bottom of the perfboard.

Circuit Design and Layout

We had a SparkFun Pro Micro (3.3V) available for this project. This device has ATmega32u4 processor which is capable of USB communication, allowing for a USB serial port to be easily created.

To interface the 12V output of the Inductive switch, a voltage divider is used.

2 LEDs are also on the board, one connected to VCC of the processor, and the other is a status LED that is controlled by the processor.

A Kicad schematic is included and shows how the circuit was prototyped, along with several images of the perf board layout.

Enclosure Design

Fusion360 was used to design the enclosure. The enclosure consists of 2 pieces that sandwich the protoyped device. The enclosure is held together using M3 heat-set inserts and fasteners.

The STL and STEP files for the enclosure are included along with the Fusion360 design file.

Software

Python 3+ is required for the provided software module. To get started, install the required dependencies:

cd software/fixture_io
pip install -r requirements.text

To create a FixtureSwitch class, simple provide the serial port that the device shows up as, for example:

• Windows: "COM1"
• MAC: "cu.usbmodem146101"
• Linux: "/dev/ttyACM0"

from fixture_io import FixtureSwitch
fixture_switch = FixtureSwitch("/dev/ttyACM0")

print(fixture_switch.get_info())
print(fixture_switch.read_switch())

The following API commands are available:

• get_info()
  • Get the company, device, and firmware version from the device
• read_switch()
  • Read the switch state
  • 0: Fixture Open
  • 1: Fixture Closed