Dual Tone MulTI-Frequency signaling is gradually used on push-button telephones worldwide. Because it provides higher dialing speed, it quickly replaces the dial pulse used by traditional rotary telephones. make. In recent years, DTMF has also been applied in interactive control, such as language menus, language mail, telephone banking, and ATM terminals. Integrating the generation and detection of DTMF signaling into any system containing a digital signal processor (DSP) is a valuable engineering application. The DTMF codec converts keystrokes or digital information into a two-tone signal and transmits it during encoding, and detects the presence of keystrokes or digital information in the received DTMF signal during decoding. Each key on the telephone keypad is uniquely determined by the line and column frequencies shown in FIG. DTMF's codec solution does not require too much computation and can be easily executed concurrently with other tasks in the DSP system. figure 1 As can be seen from Fig. 1, a DTMF signal is composed of a superposition of audio signals of two frequencies. The frequencies of the two audio signals come from two sets of pre-assigned frequency groups: a line frequency group or a column frequency group. Each pair of such audio signals uniquely represents a number or symbol. In order to generate the DTMF signal, the DSP uses software to generate two sine waves that are superimposed and transmitted. When decoding, the DSP uses the improved Goertzel algorithm to search for the existence of two sine waves from the frequency domain. This article discusses the implementation of DTMF codec on TI's fixed-point DSP chip TMS320C54x (hereafter referred to as C54x) series. 1, the generation of DTMF signals The DTMF encoder is based on two second-order digital sine wave oscillators, one for generating the horizontal frequency and one for generating the column frequency. By loading the corresponding coefficients and initial conditions to the DSP, it is possible to generate the required eight audio signals using only two oscillators. The typical DTMF signal frequency range is 700 ~ 1700 Hz, and 8000 Hz is selected as the sampling frequency to meet the Nyquist condition. figure 2 Heat film on Agriculture applications including : greenhouse seedling breeding Heating film, agricultural vegetable greenhouses heating film,,Seedling Heat Mat,Flowerpot heat mat etc.The application of heating film in animal husbandry, such as: hatching fowl heating film,far infrared sterilization heating film,etc.we are a professional and leader Chinese exporter of heat film,Customization options (for example: SMT components, flex cable and connectors) can provide the perfect complete solution that can significantly reduce assembly time and increase productivity.Providing a variety of complex shapes design, and different power designs. Membrane in the same piece electrically heated heating circuit can be designed and holding circuit,we are looking forward to your cooperation. Seedling Heat Mat Seedling Heat Mat,Plant Starter Heat Mat,Plant Seed Heat Mat,Seed Heating Pad ShenZhen XingHongChang Electric CO., LTD. , https://www.xhc-heater.com
