Measurements - Photonsters/MaskMappingTools GitHub Wiki

To measure the screen brightness as a function of position, we construct a grid that installs in place of the vat, dividing the screen into 66 10mm x 10mm sectors, and a holder for a light-dependent resistor (LDR) that fits into each grid position. This allows you to make an accurate map of your screen illumination that can hopefully later be converted into a mask to level the brightness.

  • Make the grid and LDR holder at Thingiverse. Also included are two .photon files that illuminate the entire screen for 11x 30-second intervals, allowing you adequate time to make all the measurements. One is all-white (LCD off) and one is all-black (LCD fully on).

HolderSTL GridSTL

  • Get a light-dependent resistor (LDR) and an Arduino Uno board to build this simple Arduino circuit:

Arduino LDR Circuit

  • Install your LDR into the holder. Fix it in place with a drop of adhesive behind the sensor, and wire everything up to your Uno.

LDR1 LDR2 UnoLDRMeter

  • Download the Lightmapping Arduino Sketch, and install it to your Uno using the Arduino IDE.

  • Download one of the binary Lightmapping Grid Sketches for your platform (or get the source folder and the Processing IDE). With the Arduino project connected to your PC, start the Processing sketch. If the Arduino is properly communicating with the app through the Arduino serial interface, you will see a grid of values that changes with varying light exposure atthe LDR.

ProcessingSketch

  • Download and print the .photon files at Thingiverse. When the screen is illuminated, move the LDR sensor to each position of the grid, wait for the value to settle down (about 1.5 seconds) and then click the grid position in the light mapping tool that corresponds to the position your LDR is currently measuring, to lock the value into the app. Continue this until you have measured all the positions, and have all cells showing green in the app.

Grid

  • Once you are finished, save the table as a .csv file for further analysis in excel, or other tools. Here are some example measurements displayed as surface plots, from two different Photon printers:

ChartNoLCD-photon1 ChartNoLCD-photon2 ChartLCD