Learning spectrophotometry

Introduction

You can find very expensive and powerful spectrophotometer on the market but for teaching they are most of the time a black box that can not be open.

In order to be able to better teach the technique we would like to create a simple, open source, spectrophotometer.

The idea is relatively simple. You have 4 leds (red, green, blue, white) that can be turned on / off. The beam will cross a cell, go through a slit and is diffracted using a grating film.

A linear sensor allows to analyze the intensity of each resulting wavelength.

There are 4 main parts in this project

• the electronic and microcontroller
• the microcontroller firmware
• the box
• the end-user graphical interface

Thanks to a google chrome "apps" it is possible directly from the web-browser to control the instrument. The application is available for free on the store.

Electronic and microcontroller

We played for a while with the Arduino platform and quickly found out that you can relatively easily create your own board that is compatible with the Arduino software.

This means that all the electronic can be designed to fit exactly your needs but you will still be able to program the device using the Arduino.

The linear sensor is based on the linear sensor array TSL1402R.

Buttons

In order to prevent any problems with mechanical buttons and buttons on the service, capasitive sensors are considered.

http://playground.arduino.cc/Main/CapacitiveSensor?from=Main.CapSense

Firmware

The device emulates an Arduino Leonardo and can therefore be programmed using the USB cable using the Arduino software. We currently use version 1.0.6.

The first tie the bootloader has to be installed on the microcontroller ATMega32U4.

The box

To create the box we are using:

• 123D design
• Robox 3D printer

End-user graphical interface

The user interface is based on the Visualizer and is available on the Google Apps store

Control from the terminal (Advanced users)

From a terminal on the macintosh you could currently do something like

screen /dev/tty.usbmodemfdXXX 115200

(you need to find the correct tty device using

ls /dev/tty.usb*

To kill this session

CTRL + a and then k

You are then in the terminal menu and you can enter

h + enter

For the various options.

To take a spectrum:

r + enter

You will then have 10s (blue blinking) to put the reference sample. Once the green flash appears you have 10s to put the sample.

All the results may be pasted in a view:

http://www.cheminfo.org/Spectra/Spectrophotometer/Test.html