Introduction

Light-sensitive promoters are crucial in gene expression regulation and bioengineering due to their ability to non-invasively control gene expression, reducing side effects and external interference caused by chemical inducers. This advantage is significant in in vivo experiments and therapies. However, existing light-controlled devices are limited by their narrow wavelength range, restricting the utility of light- sensitive promoters. To address this and make light-control devices accessible for all laboratories, we have designed, constructed, tested, and open-sourced Suncraft, a high-precision projector capable of full-spectrum coverage.

Fig 1. Suncraft final product

Suncraft reliably controls illumination in designated areas and creates an environment conducive to sample reactions.

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Device Budget

Frame 1

Structure Overview

Suncraft's primary components include an optical lens system, LED light source, light control module, matte black housing, and a temperature control module. The housing is 3D printed using modified PLA material, colored black to minimize ambient stray light interference. The lower part features a slide-out structure for easy sample replacement. Suncraft utilizes a Fresnel lens optical path(see Fig 2), paired with an LCD screen for image control, enabling full-spectrum illumination control of the sample. Additionally, with a PID temperature control module, Suncraft maintains a consistent temperature for the sample reactions.

Fig 2.Optical Path

Light Control Module

A typical approach for wavelength control uses a single xenon lamp and a mechanically interchangeable color filter, but this method is strict on the light source and prone to equipment damage during filter replacement. Modern laboratory requirements call for flexible wavelength adjustment and a broader range of control. Therefore, we developed a system combining an LCD screen and a color filter, achieving continuous wavelength control between 600–2500 nm.

Liquid crystals

Liquid crystals are unique materials that, when subjected to an electric field, alter their molecular arrangement and thus the transmission of light. Coupled with polarizers and filters, this enables wavelength control(see Fig 3).

Fig 3.LCD liquid crystal screen principle

For controlling the LCD screen, we selected the STC12C5608AD chip and manage it via five signals: CLK, HSYNC, VSYNC, DE, and RGB to achieve precise control. For the sake of user convenience, we have added HDMI and other external interfaces and communication protocols to the motherboard, so that Suncraft can be directly connected to the user's mobile device, directly connect the user's mobile device to the LCD screen display, and use Suncraft as the external screen of the user's mobile device to directly control the LCD screen imaging.(see Fig 4)

Fig 4.LCD control

Optical Path Design

Since liquid crystals are non-luminous, we employed a full-spectrum LED chip as the light source, driven by the FP7209 dimming chip. To maximize light efficiency and reduce scattering, a convex lens focuses the light emitted by the LED chip. To address the heat generated during long-term LED operation, which may affect experiment stability, we added a normally closed thermal control switch (automatically powering off above 70°C) and an active cooling mechanism (8mm-diameter, 6-double-sided heat pipes and cooling fan) to ensure optimal working temperatures for the LED.(see Fig 5)

Fig 5.LED driver

Fresnel Lenses

The optical path uses a combination of Fresnel lenses and reflectors. Fresnel lenses, with their grooved design, help refract and reflect light. In our design, the Fresnel lens collimates and focuses the light, converting the light emitted from the source into parallel beams, significantly enhancing the LCD screen's surrounding brightness. Virtual ray tracing simulations reveal that, compared to traditional convex lenses, Fresnel lenses eliminate solar spot effects, improving overall uniformity in brightness(see Fig 6).

Fig 6.Fresnel lens schematic

Optical Path

The optical path is as follows(see Fig 7): Light from the LED chip passes through the front Fresnel lens (145mm focal length) and is collimated into parallel beams. These beams then pass through the LCD screen, where their wavelength is adjusted, and the light is subsequently reflected and focused by the rear Fresnel lens (120mm focal length) onto the sample surface for illumination control.

Fig 7.Dynamic demonstration of the optical path

Light Control Verification

To verify the accuracy of the optical path, we used Comsol virtual simulation software to simulate light propagation, focusing on three aspects:

Collimation: Ensuring the front Fresnel lens collimates scattered light into parallel beams.
Illumination uniformity: Checking for even illumination in the target area.
Energy efficiency: Ensuring minimal energy loss through the lens system.

Temperature Control Module

Main Controller

Our main controller is based on an Arduino UNO (providing a consistent 5V output) with appropriate circuit expansion.(see Fig 8)

Fig 8.Arduino UNO

Peltier and Drive Circuit

The Peltier effect is the core working principle of the thermoelectric chip. Since the output current of the MCU's I/O port is 0-40mA, which is insufficient to directly drive the Peltier, we employed an H-bridge drive circuit composed of two BTS7960 chips. By adjusting the current direction and PWM wave input to INH, we can control heating or cooling.(see Fig 9)

Fig 9.Peltier and Drive Circuit

Temperature Sensor and Acquisition Circuit

Based on the characteristics of fast response time and wide range of temperature measurement, we choose NTC3950 as temperature sensitive element. The task of the temperature acquisition circuit is to convert the resistance change of NTC into a recognizable signal input into the main controller. We have designed the corresponding circuit: TL431CSF is used to provide stable voltage, and the voltage signal is amplified by single power operational amplifier LM321LV, and 16-bit AD converter ADS1115 with IIC interface is used to communicate with the main controller to complete the signal transmission. (see Fig 10)

Fig 10.Design of Temperature Acquisition Circuit

By preprocessing the temperature-resistance comparison table of NTC3950, the relationship between temperature and collected voltage can be established by binary search algorithm and linear Interpolation. The temperature-voltage conversion curve is shown in Fig 6. In addition, we use mercury thermometer to calibrate the temperature sensor, so that the error between temperature sensor of LviSense and mercury thermometer is within 0.5oC. (see Fig 11)

Fig 11.Temperature-Voltage Conversion Curve

PID Control

Temperature control accuracy and stability significantly influence experimental results. Proportional, Integral, and Derivative (PID) control offers a simple structure, good robustness, and ease of implementation. When the PID controller is operational, a linear combination of the proportional, integral, and derivative of the error signal generates the control quantity. This applies to the controlled object, and the control law is as follows: (see Fig 12)

Fig 12 PID

In the main controller, we discretize the above equation and unify coefficients to obtain a discrete PID control algorithm. The discrete PID expression at sampling time k is:(see Fig 13)

Fig 13 PID

Based on the required control performance, we determine the relevant parameters for the PID controller.

Arduino Code

As the code for main controller, it needs to complete the following functions:

1. Communicate with the temperature acquisition circuit to obtain the real-time temperature value
2. Communicate with the upper computer, receive the upper computer set parameters
3. Control the working condition of Peltier by PID control, and adjust temperature
4. Control the operation of the fan and laser module

Fig 14.arduino

Functional Validation

Light Control Verification

In our experiment, we employed VVD light-sensitive components that respond specifically to light with a wavelength of 450-465nm, triggering dimerization and performing their function.(see Fig 15)

Fig 15.VVD

Through literature investigation and algorithm prediction, we successfully selected and constructed a painting module based on blue-light-Inducible recombinases. In the experiment, We used Suncraft to control the wavelength of light from 450nm to 470nm to control the light of the engineered bacteria，we verified that the Escherichia coli that co-transferred the corresponding plasmid underwent protease induced expression, blue-light induced polymerization and other steps, and considerable gene editing occurred, which indicated that we could effectively use this system to control the write in of DNA stored information.(see Fig 16)

Fig 16 Light control experiment diagram

Temperature Control Verification

Early simulations indicated that the Peltier and LED chips generate significant heat, which affects the LCD screen's normal operation and impairs temperature (see Fig 16)consistency, impacting device precision.

Therefore, we designed the housing with four air inlets and two outlets, equipped with fans for auxiliary cooling. Virtual simulations analyzed the temperature variation and airflow, optimizing air circulation and heat management. The simulation results are shown in the figure. Under constant sample temperature conditions, the housing temperature does not exceed 38.5°C, and the temperatures of the LED chip and LCD screen remain below 37°C, with airflow within the housing maintaining normal operation, ensuring stable temperatures for both the LCD screen and sample. (see Fig 17)

Fig 17

Additionally, simulations of the Peltier chip's performance, combined with environmental airflow effects, demonstrated that with 6 hours of continuous operation, PID control effectively stabilizes the temperature at 37°C, confirming the reliability of Suncraft's temperature sensitivity and stability. (see Fig 18)

Fig 18

Iterative Design

After the initial design of Suncraft, we conducted extensive user surveys and received guidance from experts in the field, leading to the following iterative design improvements:

Optical System Optimization

Although Suncraft employs Fresnel lenses to reduce light scattering and improve light utilization, limitations still exist in light collimation and focusing during actual use. Experimental results revealed issues with uneven light distribution and energy loss in the Fresnel lens optical path. To address this, we plan to introduce microlens arrays to improve light distribution and minimize energy loss. Microlens arrays, composed of multiple small lenses, can effectively distribute light evenly, focus it, or change its propagation direction. By integrating microlens arrays into the optical system of Suncraft, we aim to resolve issues related to uneven light distribution and energy loss.(see Fig 19)

Fig 19

Modular Design Optimization

Replaceable Light Source Module

Although the current full-spectrum LED chip covers a wide wavelength range, certain experiments may require higher power or narrower bandwidth light sources. We propose replacing the existing LED chip with a modular, replaceable light source system that allows users to swap the LED with other types of light sources, such as lasers or narrow-band LEDs, according to experimental needs, thereby enhancing the device's versatility.(see Fig 20)

Fig 20.Replaceable Light Source Module

Expandability

Additional expansion interfaces will be added to the main control module, enabling integration of more sensors (e.g., humidity, air pressure) or external devices (e.g., fiber optic light sources, laser scanning systems), allowing the device to be flexibly extended based on experimental requirements.

User-Friendly Enhancements

Smart Control Interface

Based on early user feedback, We developed a software control interface that lets users adjust parameters like light wavelength, intensity, and temperature in real time from a mobile device, with integrated data recording functions to facilitate experimental data storage and retrieval.

Preset Experimental Modes

The software includes preset modes for common light-controlled experiments. Based on different light-sensitive promoters and experimental conditions, the system can automatically generate the corresponding light and temperature settings, reducing the operational burden on users.

Material Optimization of the Enclosure

Due to the poor heat resistance of standard PLA material, we identified limitations in high-temperature experiments. To address this, we replaced the PLA enclosure with a modified PLA material that incorporates fiberglass, improving its strength and heat resistance. Verified by experiments, this modified material can maintain good mechanical strength at temperatures up to 150°C, meeting the demands of the device.

Future Prospects

Suncraft, with its easily replaceable modules and drawer structure, boasts excellent expandability and flexibility between different applications. For example, by replacing the temperature control module with a UV transmission excitation module or a simple blackboard, Suncraft can function as a gel imager or chemiluminescence imaging device. In preliminary temperature performance verifications, it showed strong responsiveness to cyclic temperature inputs. After further optimizing the temperature control module's performance, the device may also be used for quantitative real-time PCR (qPCR) analysis.

Looking ahead, Suncraft aims to introduce an automatic calibration process using a spectrometer or other calibration devices to periodically calibrate the wavelength and intensity of the light source, ensuring long-term precision. With diverse functional modules, Suncraft is positioned to serve multiple roles in bioengineering experiments, offering a versatile tool for a wide range of applications.