For the second week experiment, we built the circuits for emitter and receiver parts respectively on the preliminary attempt, and succeeded in doing the experiment on 10th Feb morning. When we sent a message like "Hello World" in the control side, we would be able to display this message on a LCD screen through a circuit transmitted the signal by light. This bog is enriched by review of the basic process, functional or technical specifications, data dictionaries, other sources of data knowledge we've done last week.

The key process was to build the receiver circuit correctly based on the principle of photocell[1],so that we could transfer two original codes into two ardunio board dividually. The basic emitter system is able to translate the phase into digital signal(LED), hence the photocell would catch the subtle change of the LED slighting,  it was required to modify the position of two breads so that the sub-units could be in proximity to each other (as shown in Figure1).

Figure1: modification of the two breads position

Once the photocell transmit the digital signal to a current signal, the receiver part would be able to turn that back to digital through a rational bandwidth included some inevitable noise and interference.
One effective way to avoid the noise is to operate in dark environments, to bright the LED light better ( as shown in Figure2). Therefore, we could achieve a more accurate received signal on the displacement side (as shown in Figure3).

Figure2: Experimental operating in dark environment

Figure3: receive a more accurate message on another laptop

To optimize this communication system, the group members were divided into two parts for different objectives concurrently during the latter experimental hours.
For the circuit promotion testing,  the objective is to select the appropriate resistance and LEDin different colors to apply a maximum current brighter the light. Specifically, the emitter circuit withs parameters on different resistance are investigated and collected the current data of one same LED. In addition, if the resistance remained constant, the LED with different color would lead to different current (as shown in figure4).

Figure4: RED LED in constant resistance

 For LCD displacement screen process, we built the circuit followed be figure5, which required:
-Arduino Board
-LCD Screen (compatible with Hitachi HD44780 driver)
-10k ohm potentiometer
-220 ohm resistor
-pin headers
-hook-uo wires
-breadboard

Figure5: LCD screen circuit

After the combination of the two circuits into one breadboard(as shown in Figure6), the optimized system has achieved to display on LCD screen( as shown in Figure7).

Figure6: both emitter and receiver combined  in one circuit 

Figure7: LCD screen displayed detailed 

In particularly, the group have achieved the basic requirements of this project through the week2 experiment, and concentrated on enhanced design of this communication system, which required a good signal fidelity with corresponding noise filter and a ability of transmission of a large amount of information in time.

Reference:

[1]June 01, 2015 by Editorial Team, [Available]:https://www.allaboutcircuits.com/projects/an-arduino-controlled-light-sensor/