---
title: "hispec-fib"
url: "https://maker.wiznet.io/Grace_Koo/projects/hispec-fib/"
markdown_url: "https://maker.wiznet.io/Grace_Koo/projects/hispec-fib/md"
type: "UCC: User Created Content"
author: "CaltechOpticalObservatories"
author_url: "https://github.com/CaltechOpticalObservatories/hispec-fib"
editor: "WIZnet"
editor_url: "https://maker.wiznet.io/"
original_author: "CaltechOpticalObservatories"
original_url: "https://github.com/CaltechOpticalObservatories/hispec-fib"
published: "2026-03-06"
language: "en"
hardware: ["WIZnet W5500-EVB-Pico2"]
likes: 0
views: 873
comments: 0
source: "WIZnet Makers (https://maker.wiznet.io/)"
---

# hispec-fib

> An embedded control project for the fiber subsystem of HISPEC, a high-resolution spectrograph for the Keck Telescope

Original author: CaltechOpticalObservatories (source: https://github.com/CaltechOpticalObservatories/hispec-fib)

## Components

- **WIZnet W5500-EVB-Pico2** x 1 ([docs](https://wiznet.io/products/powered-by-raspberry-pi/w5500-evb-pico2))

## Documents and links

- [GitHub: hispec-fib](https://github.com/CaltechOpticalObservatories/hispec-fib) (code)

## Article

## HISPEC-FIB

**Fiber Subsystem Control Project for the HISPEC Astronomical Instrument**

![W. M. Keck Observatory - Wikipedia](https://upload.wikimedia.org/wikipedia/commons/a/af/KeckTelescopes-hi.png)

*https://en.wikipedia.org/wiki/W._M._Keck_Observatory*

> **Caltech Optical Observatories (COO)** is an astronomical research organization at the California Institute of Technology (Caltech), managing the Palomar Observatory and Caltech's participation at Keck Observatory, while developing advanced instrumentation for both facilities.

| Item | Details |
| --- | --- |
| Organization | Caltech Optical Observatories (COO) |
| Target Instrument | HISPEC — W. M. Keck Observatory (Keck II Telescope) |
| Subsystem | FIB (Fiber Injection Bench / Fiber Subsystem) |
| Embedded Board | **W5500-EVB-PICO2** (RP2350 + WIZnet W5500) |
| Tech Stack | Python (lightpath/throughput model), C++ FreeRTOS (embedded), Zyre-like TCP/UDP, mKTL |
| Controlled Components | 7 components: TIB, CAL B/R Fiberswitches, Achromatic Splitter, Blue/Red Main Switches |
| Document Reference | Jeb Bailey, August 2025 (internal technical documents + source code) |

---

## 1. Background

HISPEC (High-resolution Infrared Spectrograph) is a high-resolution infrared spectrograph being developed by Caltech Optical Observatories for the W. M. Keck Observatory in Hawaii.

`hispec-fib` is the software project that controls FIB (Fiber Subsystem), which manages the routing of light through the instrument.

- Configures optical paths in real time across tens of meters — from the Nasmyth platform down to the spectrograph room

- Controls switches and fiber connections to direct science light (for observation) and calibration light (for instrument calibration) along the correct paths

- Reconfigures the full optical path flexibly depending on the science objective, such as exoplanet atmosphere characterization or precision radial velocity measurements

---

## 2. Controlled Components: 7 in Total

FIB consists of 7 components distributed across physically separate locations.

| Component | Location & Role |
| --- | --- |
| TIB (Trunk Interface Box) | Below the Nasmyth platform in the Keck dome. Central control box managing 6 laser sources, variable attenuators, and photodiodes |
| CAL B Fiberswitch | B Calibration rack. Switches calibration light paths for the blue channel |
| CAL R Fiberswitch | R Calibration rack. Switches calibration light paths for the red channel |
| Achromatic Splitter (AS) | Main Switch rack. Handles both B/R channels simultaneously. Splitting ratio software-controlled |
| Blue Main Switch | Main Switch rack. Mechanical XY-stage fiber switcher + USB fiber tip inspection camera |
| Red Main Switch | Main Switch rack. Identical design to Blue Main Switch |
| RaspberryPi | Main Switch rack. Dedicated host for Blue/Red Main Switch USB cameras |

> **Note:** The first four components (TIB, CAL B/R, AS) share a common PCB design and all use the W5500-EVB-PICO2 board. The two main switches are a separate design based on a vendor-supplied PLC and fiber imaging cameras.

---

## 3. Hardware Configuration

The actual hardware configuration of the embedded controllers is clearly documented in `embedded/docs/breadboard.md` and `embedded/docs/status.md`.

### Main Controller Board

The [**W5500-EVB-PICO2**](https://docs.wiznet.io/Product/Chip/Ethernet/W5500/w5500-evb-pico2) is the core board used across the embedded controllers including the TIB. It integrates an RP2350 (dual Cortex-M33, 264KB SRAM, 2MB flash) and a WIZnet W5500 Ethernet controller (SPI-based TCP/IP offload, integrated PHY + RJ45) on a single board, with the W5500 connected via SPI0 (GP16–21).

### Peripheral Device Configuration

| Device | Role | Interface |
| --- | --- | --- |
| ADS1115 (16-bit ADC) | 2-channel photodiode measurement | I2C0 (GP4/GP5), addr 0x48/0x49 |
| DAC7578SPW (8ch DAC) + OPA2991 OpAmp | Controls 6 variable optical attenuators | I2C1 (GP2/GP3), addr 0x4C |
| PCAL6416A (I2C 16-GPIO expander) | Controls 8 MEMS optical switches | I2C1 (GP2/GP3), addr 0x20 |
| Maiman SF8250-ZIF14 | 6 laser diode drivers | UART1 (GP8/GP9), RS-485 |
| Level Shifter (Phillips 4-bit bidirectional) | 3.3V ↔ 5V level translation | — |
| Power Switch | Power control for photodiodes and laser drivers | GP6 |

> `embedded/docs/notes.md` documents the W5500 driver selection process. Both the WIZnet-PICO-LWIP-C and WIZnet-PICO-C examples were evaluated. After identifying a build bug in the latter's W5500 Pico2 support (related to `#if 1`), the team opted to integrate the ioLibrary_driver directly.

---

## 4. Software Architecture

![](https://maker.wiznet.io/upload/ckeditor5/369174851%5F1773401854%2Epng)

*Generated by Gemini*

### 4-1. Embedded Firmware (C++ / FreeRTOS)

The embedded codebase is a multi-task C++ structure built on FreeRTOS, with three core design principles: "no runtime exceptions", "static memory layout", and "single ownership". Network communication (`coms_task`), command dispatch (`executor_task`), and asynchronous photodiode polling (`photodiode_task`) run as separate tasks, and each hardware device — MEMS switches, lasers, and attenuators — is abstracted into an independent device object.

#### Communication Protocol: Zyre-like

The design documents describe an MQTT-based interface, while `embedded/docs/status.md` describes the actual embedded implementation using a **Zyre-like TCP/UDP messaging** layer. The two are inconsistent within the same repository, and the final implementation has not been fully verified at the source code level.

- **ENTER**: UDP broadcast for dynamic network self-discovery

- **WHISPER**: TCP-based 1:1 command reception (mKTL command path)

- **PUB**: Asynchronous data publishing (photodiode telemetry, etc.)

Networking is DHCP-based and designed to automatically restart DHCP after a link loss.

---

### 4-2. AIT Modbus Tool (`modbus_communication.py`)

The Modbus code under `ait/photonic_testing/maiman_modbus/` is **not operational control code**. As the path implies, it is a tool used during AIT (Assembly, Integration and Test) to directly test the Maiman laser drivers over RS-485/Modbus RTU.

Built on `minimalmodbus` + `pyserial`, it provides register-level read/write and multi-register access. In production, lasers are controlled via UART RS-485 from the embedded firmware — the Modbus tool serves a separate role for hardware validation during integration testing.

---

### 4-3. LightPath Manager (`lightpath.py`) — A Working Optical Simulator

`lightpath.py` is not a design sketch — it is **executable Python code**. It represents HISPEC's entire optical system as a graph and computes spectrum propagation through it.

Each optical component (fibers, switches, WDMs, attenuators, lasers, photodiodes, spectrographs) is modeled as a Python class, and `LightpathManager` owns the full connectivity graph.

#### Path Traversal

When switch states change, the active optical paths change with them. `LightpathManager` performs a DFS over the graph reflecting the current switch states, accumulates the `TransmissionCurve` product along each path, and sums the spectra arriving at each detector.

---

## 5. Role of WIZnet W5500

Confirmed roles based on `embedded/docs/status.md` and `breadboard.md`.

| Role | Details |
| --- | --- |
| **Network connectivity layer for embedded controllers** | W5500 connected to RP2350 via SPI. WIZnet ioLibrary Driver integrated directly to provide hardware TCP/IP stack. DHCP-based network participation with automatic reconnection after link loss |
| **mKTL-based command delivery channel** | Receives mKTL JSON commands from upper-level control software over TCP and delivers them to the embedded controller |
| **Telemetry collection and upper-level software integration** | Asynchronously sends photodiode polling results to the upper-level system. SNTP time synchronization is not yet implemented |

---

## 6. Technical Notes

**Hardware control and physical model in the same context**: Hardware command execution and optical path simulation coexist in the same operational context. When a laser setting changes, the effect on the spectrum reaching the spectrograph can be reasoned about directly within the software.

**Clear separation between AIT and operational code**: The Modbus code under `ait/` and the FreeRTOS code under `embedded/` are clearly separated. The same hardware (Maiman laser drivers) is accessed via Python Modbus during AIT and via embedded UART in production — a structure that prevents code confusion during the handoff from integration testing to operation.

---

## 7. Current Development Status

**This project is actively under development.** It is not a finished product — it is in an integration validation stage where some components are functional and the architecture is finalized, but work remains.

---

## FAQ

**Q. Why is the WIZnet W5500 specifically necessary for this project?**
The FIB embedded controllers need to handle TCP command reception and telemetry transmission simultaneously in a DHCP-based Ethernet environment. The W5500 provides a hardware TCP/IP stack over SPI, reducing the software burden on the RP2350 while maintaining stable network connectivity. This is particularly valuable in a FreeRTOS environment where network tasks must not interfere with real-time hardware control tasks.

**Q. Can the W5500-EVB-PICO2 be replaced with a different board?**
This board is explicitly specified in the design documents, and the WIZnet ioLibrary Driver is directly integrated into the codebase. Substitution with another W5500-based board may be possible, but the current code is written around the RP2350 + W5500 pin layout and SPI configuration.

**Q. Can this project's architecture be applied to other instrument control or industrial environments?**
The component-graph structure of the LightPath Manager and the task-separated embedded firmware design are both worth referencing for other multi-device optical control systems, beyond HISPEC-specific parts. That said, since the project is still under active development, APIs and interfaces are subject to change.

**Q. How can I run the code locally?**
The Python side (`lightpath.py`) can be run without hardware by installing dependencies such as `synphot`, `astropy`, and `scipy` — enough to explore the optical path simulation. The embedded firmware requires a W5500-EVB-PICO2 board, the Pico SDK, and a FreeRTOS build environment.

---

Source: https://maker.wiznet.io/Grace_Koo/projects/hispec-fib/