Transparent Film Heater from Fullchance

Transcription

1 Transparent Film Heater from Fullchance AN0103 Application Note Abstract There are numerous applications which require heater functionality with clear optical transparency and possibility to be applied to a complex curved surface. With fullchanc film it is possible to build multi -functional systems with functional modules that operate together or independently. This article provides an overview of the demonstration design comprising a transparent heater with temperature control capacitive sensing buttons implemented on a single film. Introduction Sudden changes in temperature and excessive humidity may cause moisture condensation, freezing and icing of viewing surfaces. Also, operating at temperatures at or below manufacturer s recommendations, may cause some electronic devices (like LCD-displays) to react very slowly or improperly. To enable the operation of technical devices in extreme conditions, and create more comfort for a user, the means to eliminate the impact of adverse weather conditions become a matter of interest. The application of a heater is one solution to the problem. Transparent heaters are visually transparent substrates with electrically conductive coatings that use the principle of resistive heating, also known as Joule heating. It is the process of generating heat by electric current flowing through a conductor. Transparent heaters are typically used for anti-fogging, anti-icing and de-icing of hardware in many diverse applications including outdoor LCD displays and outdoor computers, handheld electronic devices, LED headlamps in automotives, traffic lights, windows, mirrors, camera lenses, touch screens and any other that requires light or visual transmittance in cold and moist environments. Fullchance Next Generation of Transparent Heaters Selection of the material class combining high electrical or thermal conductivity, optical transparency and flexibility is crucial for the development of many electronic and optoelectronic devices. Fullchance technology based conductive material shows reliable results and represents a viable alternative to the commonly used solutions (like scarce and brittle ITO). April 17, 2014 AN0103 Transparent Heater with Capacitive Controls on a Single Film 1

2 Fullchance film have the advantage of the high transparency at 10x better conductivity than ITO in addition to greater mechanical flexibility comparing to other solutions. The mechanical flexibility of Fullchancefilmallows applying the heating design to applications with curved surfaces (see Figure 1). In addition, Fullchance based transparent heat ing film is able to be transferred onto different substrates. This allows expanding the variety of materials for which the heating can be applied and as result widening the products area coverage. Key advantages of the Fullchance based transparent heaters: High transparency at low resistance (high conductivity) Faster heating rates than ITO-based transparent heaters Uniform heating with resistance tolerances of ± 20% Mechanical robustness allows heating in applications with curved surfaces Multiple conductive paths increases heating robustness and reduces likelihood of heater failures caused by damaged film All of the material s benefits make Fullchance film based heaters believe to be next generation of transparent heaters. Figure 1 illustrates the benefit of Fulchance film usage for a visor surface defogging and snow melting. Figure 1. Fullchace conductive film used in visor heating applications Visor Heater Demonstration Design The purpose of the Visor Heater design is to demonstrate that conductive Fullchance film enable application of a thin-film heater to curved transparent surfaces. Additionally, capacitive touch sensing controls were developed to allow user adjustment of the visor heating temperature. The distinctive feature of the design is that both functional parts (heater and sensing controls) were implemented on a single transparent conductive film. April 17, 2014 AN0103 Transparent Heater with Capacitive Controls on a Single Film 2

3 Device Construction The plastic visor that is a typical element of a snowmobile helmet was chosen as an object to heat. The idea was to develop the visually transparent heating system for a visor surface to prevent its fogging, frosting or icing. Figure 2 shows the general view of the developed demo device. Figure 2. General view of Visor Heater device Figure 3 shows the construction details of the Visor Heater device which consists of the visor with transparent heater installed (A), silver paste (MSE2010L) conductive lines (B), touch sensing buttons for heating temperature control (C), device control board (D), thermometer strip (E) and plastic mount base (F). Figure 3. Construction details of Visor Heater device E D A C B D C F E B A April 17, 2014 AN0103 Transparent Heater with Capacitive Controls on a Single Film 3

4 The function of the transparent heater and capacitive touch sensing buttons are implemented by the use of Fullchanc conductive film. The film is laminated on the visor surface using two-side 3M 468MP adhesive transfer tape. Two capacitive touch sensing buttons are located on the right side of the visor surface. The buttons provide an interface to allow user control of the desired heating temperature. Table 1. Function of temperature control buttons Control element Layout Function Button 1 Increases the visor heating temperature by 1 C Button 2 Decreases the visor heating temperature by 1 C The purpose of the device control board is to supply and adjust power to the heater element. The board comprises all of the device electronics (see Figure 4). Cypress microcontroller CY8C PVXI is used as a circuitry basis for the device (this is shown as element (1) of Figure 4). The 7- segment LED indicator (2) displays the temperature set in C) using touch sensing buttons. The Q1 and Q2 transistors (see schematic in Appendix) are used to drive the heater circuit (3). Q1 acts as a driver for Q2 which in turn is used as a high side switch. The demo design uses 12V power supply. The connector to supply power to the board is shown as (4). There is also a reset button (5) on the board; ISSP\I2C connector (6) to program device and send debug data through I2C interface; Fullchance film connector(7) to connect the heater and sensing buttons traces with the device board. Figure 4. Device control board April 17, 2014 AN0103 Transparent Heater with Capacitive Controls on a Single Film 4

5 The flexible thermometer strip is stuck on the visor surface to visualize the temperature of the warmth created by the heater. The strip contains six graphical sections allowing to indicate temperature in the range from 35 to 0. Each section corresponds to certain temperature. Once the temperature of the heater surface reaches the strip measuring range the appropriate indicating section will highlight. The design mount is made of a thick 235 x 290 mm plate made of 5 mm acrylic plastic. It is used to hold all the design constructive parts and prevent flexible and delicate parts from damage. To ensure an accurate application of the transparent heating film to the visor surface a specific pattern was developed. Figure 5 shows the pattern shape and its basic dimensions. Figure 5. Heating film pattern 513 mm ø28 ø mm From the figure above: 1 visor heating area; 2 conductive silver paste electrodes; 3 touch sensing buttons for temperature control; 4 visor clamping holes. Firmware The firmware for the Visor Heater device was developed using Designer 5.4 integrated development environment (IDE). ypress Semiconductor s PSoC Firmware components used in the PSoC Designer project and their function: CSD user module is used to measure buttons capacitance. PWM user module is used to control the heater temperature. Its duty cycle depends on the buttons input. EzI2Cs user module is used for debugging purposes. Firmware routines are used for optimal functionality of 7-segment LED indicator to display the target temperature. April 17, 2014 AN0103 Transparent Heater with Capacitive Controls on a Single Film 5

6 Figure 6 shows the chip editor of PSoC Designer 5.4 and the other system settings of the Visor Heater project. In order to improve signal-to-noise ratio and increase detection distance the 5- elements median and infinite impulse response (IIR) software filters were used in the project. Figure 6. Chip Editor view of the project in PSoC Designer Figure 7 shows the high-level operation block diagram of the Visor Heater design. Every time the device is powered ON all the components are initialized. After that the Force heater start stage provides a quick settling of the heating start temperature, which is 35. Then the temperature control buttons are being scanned. Once the button input has been detected it is processed. Then the appropriate data of the user defined temperature is displayed on the 7-segment LED indicator and a PWM module outputs the signal with the corresponding duty cycle. The system is inertial as there is no actual temperature sensor used and no feedback loop to control the temperature. This design could be expanded to include a temperature sensor, thereby allowing for full closed loop control of the heater drive. April 17, 2014 AN0103 Transparent Heater with Capacitive Controls on a Single Film 6

7 Figure 7. High-level operation block diagram of the Visor Heating device Start System initialization Force heater start Scan buttons Process buttons input Display temperature Temperature control Achieved Results A set of tests were conducted to ensure reliable operation of the device: testing of heating appliance, checking the influence of the heating film part on capacitive sensing buttons and power consumption at different heating temperature settings. The temperature displayed on the 7-segment LED indicator is that which the heater is trying to reach at the moment and it does not set at once. The settling time may vary depending on environmental conditions. A compliance of the visor surface temperature with the target heating temperature specified by user was checked with the thermometer strip. All of the development and testing were done in office room temperature 22 ) conditions. Capacitive Buttons Performance Parameters The button noise values and signal-to-noise ratio (SNR) were measured to make sure that the heating area does not exert influence on the touch sensing part. The buttons SNR was calculated based on the noise peak-to-peak value (Npp) and mean value of the touch signal. The root mean square (RMS) noise value of the signal samples was evaluated to show that the noise variations are acceptable. Table 2 indicates data on calculated Npp, RMS and SNR. Figure 8 illustrates the measured noise and touch signal for the temperature control buttons. It was determined that the buttons have the similar noise and touch sensing signal values for all temperature April 17, 2014 AN0103 Transparent Heater with Capacitive Controls on a Single Film 7

8 settings (35 to 40 ). The figure illustrates the noise data for 35 temperature setting and the touch sensing while increasing temperature from 35 to 36. Figure 8. Measured noise and touch signal from the buttons: (a), (b) noise signal of non-touched buttons; (c), (d) buttons touch signals; a) b) Button1 noise/touch signal Button2 noise/touch signal c) d) April 17, 2014 AN0103 Transparent Heater with Capacitive Controls on a Single Film 8

9 Table 2. Noise and touch signal correlation metrics Parameter Button1 Button2 Comment Npp Npp = Max(Noise value) Min(Noise value) + 1 RMS RMS noise of the signal samples SNR Mean signal value / Npp The calculation above performed on 100 samples of measured signal data, with and without touch. The SNR for buttons is high enough. The noise level is around points, which is acceptable. Table 3 shows the measured values of the device consumed current for six different heating temperatures. Table 3. Device current consumption Heating Temperature Consumed Current A A A A A A In the Force heater start stage (see Figure 7) the device consumes 3.2 A. Conclusion The proposed demonstration design shows that usage of Fullchance conductive material allows implementation of an economical and technically rational multi-functional system comprising functions of the transparent heater with touch sensing based temperature controls on a single film. April 17, 2014 AN0103 Transparent Heater with Capacitive Controls on a Single Film 9

10 Appendix Figure 9. Schematic of the Visor Heating design April 17, 2014 AN0103 Transparent Heater with Capacitive Controls on a Single Film 10

11 References Document History Revision Date Changes ** 17-Apr-2014 Initial release. Transparent Film Heater For Helmet For Questions and Comments: opyright, 2014 April 17, 2014 AN0103 Transparent Heater with Capacitive Controls on a Single Film 11