Program features: * Support button, slider and wheel touch interface; * Less hardware resources, 2 timers and GPIO ports; * Fewer peripheral devices, only two resistors and one capacitor per channel, low manufacturing cost; * MCU is automatically calibrated after power-on, the manufacturing process is simple; * Sensitivity can be adjusted, with high adjustability. Applications: Mobile phones, VCD, DVD, induction cooker, range hood, water heater, washing machine, microwave oven, coffee machine, refrigerator, MP3, MP4, DPF digital photo frame, CAR DVD, etc. In applications of large-capacity, high-visibility products such as portable media players and mobile handheld terminals, touch buttons have been widely adopted as an interface technology. Due to the advantages of convenience, ease of use, fashion and low cost, more and more electronic products begin to shift from traditional mechanical buttons to touch buttons. Based on the capacitive touch sensing key scheme of the LPC1100 series Cortex-M0 microcontroller, the GPIO port of the LPC1100 and two internal timers can be used to realize the application of up to 24 independent buttons or slider capacitive touch buttons. This solution uses peripheral RC circuit plus software detection technology, integrated FIR filter algorithm, has good anti-interference performance, can pass the EFT (Pulse Group Anti-Interference Test) 4KV index, very suitable for electronic equipment driven by alternating current. Principle overview The basic principle of the capacitive touch-sensing button is shown in Figure 1. When the human body (finger) touches the metal sensor plate, since the human body is equivalent to a capacitor connected to the ground, a capacitor will be formed between the sensor plate and the ground. The capacitance is usually a few pF to tens of pF. Using this most basic principle, building related circuits externally, you can detect whether a human body touches the metal sensor according to this change in capacitance. Figure 1 Principle of capacitive touch sensing The principle of capacitive touch-sensing buttons based on the LPC1100 series Cortex-M0 microcontroller is shown in Figure 2. Using the GPIO interrupt function of the LPC1100 and an internal timer, it is easy to measure changes in external capacitance. The processing flow is as follows: * Initialize KEY n as a GPIO port, you must turn off the internal pull-up function, and configure it to neither pull-up nor pull-down mode; * Enable and configure the high level interrupt of KEY n; * Set KEY n to output, and output low level, at this time the capacitor discharges; * Turn on the timer, configure KEY n as an input, and turn on the high-level interrupt. At this time, the capacitor starts to charge, and the timer time is read in the interrupt service function of KEY n; * According to the change of this charging time, it can be judged whether there is a key press. Figure 2 Based on the principle of LPC1100 touch buttons Note: Figure 2 only shows two independent button connection schemes. Up to 24 independent buttons or sliders can be connected using the GPIO input inside the LPC1100. The charge and discharge waveforms of the RC circuit charge and discharge with or without human touch are shown in Figure 3. When the GPIO is configured as an input to charge the capacitor Cx, if there is no human touch, the charging and discharging curve of the capacitor is shown in the green line in Figure 3; when there is human touch, the human body brings an inductive capacitance, then the capacitor is The discharge rate becomes slow, as shown in the red line in Figure 3. Using this time change, coupled with the GPIO interrupt detection function, you can determine whether there is a key press. Figure 3 Schematic diagram of charging and discharging of the RC circuit with or without human touch Solution features * Support button, slider and wheel touch interface; * Less hardware resources, 2 timers and GPIO ports; * Fewer peripheral devices, only two resistors and one capacitor per channel, low manufacturing cost; * MCU is automatically calibrated after power-on, the manufacturing process is simple; * Sensitivity can be adjusted, with high adjustability. Application Capacitive touch-sensitive buttons have the advantages of not being afraid of wear, not affected by temperature and humidity, waterproof protection, and low cost. Therefore, it has been widely used in mobile phones, VCDs, DVDs, induction cookers, range hoods, water heaters, washing machines, microwave ovens, coffee machines, refrigerators, MP3, MP4, DPF digital photo frames and CAR DVD. Physical picture
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