The housing should be printed upright. No structural supports should be needed. The printer filament used for this design was PLA; however, any filament should work equally well. If the 3D printer being used is too small to print the housing in one piece, the housing can be sliced, printed in several pieces, and epoxied together. 

Assemble the circuit following the circuit schematic seen in the images.

Place bar through apparatus and attach nuts so as to "sandwich" the walls between the nuts. Heat shrink or electrical tape can be placed on bar to make it more comfortable for the rat. Attach sensors to inside nuts and face them toward each other. 

Download and install the Arduino IDE from https://www.arduino.cc/en/main/software. Open the Arduino IDE and navigate to Sketch/Include Library/SD. Download LiquidCrystal_I2C.h from https://drive.google.com/file/d/14VPCVHqlfbtxAn5LCF3tGZytkGEMrk3Q/view and place it in the Arduino Libraries folder. Download the “Counter.ino” program. Flash code to Arduino. The Arduino IDE is compatible with all major operating systems.

The LCD display will count in 1/100th seconds when the IR beam is broken. When the beam resumes, the count will stop. After a period of 3 seconds, the beam can be broken again to restart the time, or the push button can be pressed to save the current value. This 3 second delay allows for the rat to be removed from the apparatus without the experimenter accidentally clearing the count. Adjust the height of the bar to an appropriate height for the size of the rat. Place the rat’s forepaws on the bar quickly as the count will start immediately upon the beam being broken. After the rat’s removal of itself from the imposed posture, the LCD will then display the current rat ID and the time in min:sec.hundredths (00:00.00) format. Press the push button to add the recorded time to the data module.