Previous experiment realized the basic light transmitting function of the system and variety of information is also available to be transmitted. While, LED and photo diode should be placed very closely to each other, or there will be much noise detected on the receiver side. To solve this problem, a lens is used to improve this problem.
Lens is the equipment to focus or disperse light [1]. In our project we used a lens to focus the light on the detector. The parameter focal distance of the lens is 10cm. The lens is placed between LED and photo diode, while the lens is close to LED and 7-8 cm away from the photo diode. (This distance is discovered by moving the lens and choosing the point with the best result. It is revealed in Figure 1) This lens enables the detector and LED separated and information transmitted over some distance. The following video showed the experiment result of using lens.
Lens is the equipment to focus or disperse light [1]. In our project we used a lens to focus the light on the detector. The parameter focal distance of the lens is 10cm. The lens is placed between LED and photo diode, while the lens is close to LED and 7-8 cm away from the photo diode. (This distance is discovered by moving the lens and choosing the point with the best result. It is revealed in Figure 1) This lens enables the detector and LED separated and information transmitted over some distance. The following video showed the experiment result of using lens.
Figure 1: system with the lens
To improve the stability of the system, the final version of amplifier and filter is decided, which is shown in Figure 2.
Figure 2: simulated receiver circuit
The TL073 is applied in this system. It is a
low noise operational amplifier (18nV voltage
noise density) is an excellent analog building block for designing low noise
differential circuits. The typical gain bandwidth of this amplifier is 100MHz
and op amp slew rate is sufficient for signal frequencies up to 5MHz.
Since the output voltage follows the input, a
basic non-inverting op-amp circuit, which is also called as a voltage follower,
has been designed in the project to amplify the input voltage. Feedback control of the non-inverting operational
amplifier is achieved by applying a small part of the output voltage signal
back to the inverting ( – ) input terminal via a voltage divider network, again producing negative feedback as
shown below. This closed-loop configuration produces a non-inverting amplifier
circuit with very good stability, a very high input impedance.
Figure 3 is the final version of our visible light communication system. This system shows the ability to complete visible light communication with the acceptable level of stability.
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| Figure 3： Visible light communication system |
Reference
[1] Wikipedia, "Len(optics)'' [Online]
Available: https://en.wikipedia.org/wiki/Lens_(optics)
