A Python interface for StellarNet spectrometers designed to provide the functions of a Spectronic 20 spectrophotometer including an LED light source
The StellarNet drivers need to be requested from the company. To get the drivers you will need to complete a Software License Agreement with them (https://www.stellarnet.us/wp-content/uploads/StellarNet-SLA.pdf). This project offers a working frontend without violating the license agreement.
The goal of this project was to replace the old Spec 20s in our teaching laboratories with equivalent functionality in modern equipment. Choices of hardware and software were driven largely by familiarity. The choice of the Raspberry Pi was to make an effectively disposable computer. I picked Python 3.x (the older branch works on Python 2.7) for simplicity in migrating to different hardware. What I created here is a simple frontend for the spectrometer suitable for use by relatively untrained undergraduate students.
The project was written to support undergraduate laboratories, so really this repository is for people looking for a frontend to run their spectrometer. However, the functionality of the project can readily be expanded to take advantage of the spectrometer features. This code takes care of collecting the spectra and controlling the light source, everything else is just manipulations in code. Simple changes in the code shift the interface from having lots of things chosen for you to needing to make lots of choices. For example, there is a 'Save Button' commented out in the code. If you uncomment the 3 lines of the GUI for the button, the Save function is fully implemented.
The master branch works on newer (as of May 2024) Python 3.x versions. Separate branches for Python 2.7 and older 3.x versions are available. I wrote this on a Raspberry Pi 3b+. The master branch was tested on Python 3.9 and 3.11 with Raspbian OS Bullseye and Bookworm. The Bookworm distribution is slow on a 3b+, and not entirely recommended.
For Windows or Mac you will need to make small changes to the code to deal with OS peculiarities. You will need to possess a Stellarnet spectrometer. The LED requires building a small circuit to allow pulse width modulation of the LED for brightness control. The schematic is below. I built this on a Pi-topPROTO board which made it even easier.
For Raspbian OS, the apt-get package manager was used for sytem packages. For other Linux types, the appropriate package manager (e.g., yum for CentOS) will depend on your Linux distribution. The pip or pip3 (depending on your Python set-up) get the Python packages. Note that on Raspbian starting with the 'Bookwork' distribution, pip installs must be to a virtual environment to obey the stricter versioning rules.
For Windows and MacOS, one would typically use pip to install Python libraries. Help with pip is available at https://packaging.python.org/tutorials/installing-packages/
- libusb-1.0-0-dev (with apt-get)
- pyusb 1.2.1 (Linux example: pip3 install pyusb==1.2.1) this is version specific, so consider using venv
- numpy 1.24.2
- matplotlib
- (May 2024) may need to also get
sudo apt-get install python3-pil.imagetkto address an import error from matplotlib - screen (if you want to hide the background processes)
- pigpio {already part of Raspbian} (for Raspberry Pi control of the LED)
99-local.rulesneeds to be copied to '/etc/udev/rules.d/' or update the existing .rules file to include rules for StellarNet devices. Otherwise you would need to run as root to get USB access.- Stellarnet has dramatically simplified the installation process since 2019, so there is a lot less for the user to manage.
- the rest of the files in PiSpec20_stellarnet should go into the same directory. The drivers from StellarNet should be placed in a folder within this directory.
- on a Windows system, there is an extra step in the driver installation. See the documentation from StellarNet.
- fresh install of Raspbian Bullseye
sudo apt-get install libusb-1.0-0-devpip3 install pyusb==1.2.1pip3 install numpy==1.24.2pip3 install matplotlibsudo apt-get install python3-pil.imagetksudo systemctl enable pigpiodthis makes the GPIO always available. One time use would besudo pigpiod.- copy this repository
sudo cp 99-local.rules /etc/udev/rules.d/99-local.rules- copy StellarNet drivers to the PiSpec20_LED_stellarnet folder
sudo chmod +x run_hiddento make the bash script executable. A batch file would substitute the bash script on Windows.- reboot
- a USB connected StellarNet spectrometer
- a PWM circuit and LED. The easiest way to do this would be on a Raspberry Pi since it has PWM pins ready to use. Other prototyping platfoms (Arduino, etc.) could be adapted easily. From a 'standard' PC, a PWM circuit can be attached by USB (Yocto, etc.). An acceptable LED for "white light" illumination can cost as little as $2.00.
| Manufacturer | Spectrometer | Works ? |
|---|---|---|
| StellarNet | Black Comet | yes |
| Spectrometer | Linux driver | Windows driver |
|---|---|---|
| Blue Wave | x | x |
| Black Comet | x | x |
| Silver Nova | x | x |
| High Resolution | x | x |
| Green Wave | x | x |
I don't write in Python for a living, nor particularly do a lot of programming. And it shows in the code.
If you wish to contribute please contact me.
MIT license