# Implementation of Adaptive Real-Time Camouflage System in Visible-Light Band
## 3 Results and Discussions
### Results of PWM Signals  
After the serial port configuration, the Raspberry Pi sends data, and the pulseview tool is used to connect the TXD pin of CH341T to capture data sent by the Raspberry Pi. Figure 7 shows that the captured data sent by the Raspberry Pi contained one start bit, eight data bits, and one stop bit.  
In this study, the host Raspberry Pi was connected with two M0518 SD2 AE MCUs, as shown in Figure 8. The first slave M0518 SD2 AE MCU outputted the PWM signals with duty ratios of 10%, 20%, 30%, and 40%, as shown in D0, D2, D4, and D6, respectively, and the second slave M0518 SD2 AE MCU outputted the signals of D1, D3, D5, and D7, respectively. Each M0518 SD2 AE MCU can only output 24 PWM channels, and therefore multiple slaves are required to work together when displaying a complete camouflage image.  
Figure 9 shows the input and output signals of high-voltage modulation circuit. The high-voltage AC can be conducted or cut off using the PWM driving signal. The photo-coupler isolates the control circuit from the high voltage electrodes to suppress interfaces.  
Figure 6: Comparison of matching results between the method we proposed and the HSV gray histogram analysis method. (**a**) The correlation coefficient with \(\Lambda\); (**b**) the correlation coefficient with G.  
Figure 7: The measured serial communication waveform by the pulseview tool.  
Figure 10 shows the relationship between the duty cycle and RMS value of output voltage. After curve fitting, the relationship between output voltage and PWM duty cycle is expressed as  
\[V=\left\{\begin{array}{cc}23.27+5.8d-0.07d^{2}+3.62d^{3}&0<d\leq 100\\ 0&d=0\end{array}\right. \tag{6}\]  
where \(V\) is the output voltage RMS, and \(d\) is the PWM duty ratio.  
Figure 8: PWM signals with different duty cycles generated by M0518 SD2 AE MCU.  
Figure 9: The input and output signals of high-voltage modulation circuit.  
Figure 11 shows the movement of the reflection band of the CLCs under different voltages. The peak wavelength of the reflective band of CLCs was shifted from 604 to 544 nm with the voltage tuned from 0 to 250 V. After taking the environment image, the physical driving waveform generation part outputs the corresponding voltage signal to make the CLC device display the similar color with the environment for the purpose of camouflage.  
Figure 12 shows the adaptive camouflage system, which includes environmental images (grass images), cameras, Raspberry Pi, M0518 SD2 AE MCU, transformer, photo-coupler ELM3064, signal generator, and oscilloscope. The camera (PI NOIR CAMERA V2) captures the grass image. After image acquisition and matching, the host Raspberry  
Figure 11: The movement of the reflection band of the cholesteric liquid crystals (CLCs) under different voltages.  
Figure 10: The relationship between the PWM duty cycle and the RMS value of the output voltage.  
Pi transmits the PWM duty cycle signal to the two M0518 SD2 AE MCUs to output PWM signals through USB-TTL(CH341T) unit. The AC voltage signal with a frequency of 5 Hz and an amplitude of 3.3 V is provided by signal generator (AFG31000). The high-voltage AC voltage with the maximum RMS value of 250 V is generated by a transformer, and then a modulated 0-250 V RMS amplitude adjustable AC voltage is realized by the photo-coupler ELM3064. The 0-250 V output signal is collected by oscilloscope (MDO3012). Table 4 shows the comparisons of system performance. The response time of the proposed system is reduced to 1.71 s, while a wider response wavelength range, stronger anti-interference ability can also be obtained.