Arduino

在使用超声测距模块时，需要给超声模块一个方波信号。于是可以用树莓派的的PWM功能产生一个低频的方波信号。 产生方波信号后，如果手边没有示波器，还可以使用Arduino的ADC采样功能，做一个简单的示波器。 树莓派产生方波 树莓派的pin12、pin33(GPIO_18、GPIO_13)是树莓派提供的PWM硬件接口，可以产生高频的PWM信号。 由于我只需要产生一个大约50Hz的方波信号。用最简单的GPIO库就可以产生可用的方波。 ...

Arduino可以使用PWM产生方波信号，在我的Arduino UNO R3上，支持PWM的输出口是pin 3,5,6,9,10,11这几个引脚，支持大约980Hz的PWM输出。这方面不再赘述。 本文介绍另一种产生方波的方法，可以使用任何引脚产生方波信号。功能： 固定频率，占空比，偏移量的方波 通过模拟口连接可调电位器，产生可变频率、占空比、偏移量的方波 // High-accuracy square wave generator // based on Arduino UNO // with runtime adjustable frequency, PWM width and offset // Output wave at pin 13 double freq; // Hz double offset; // percent (0.0 to 1.0) double width; // percent (0.0 to 1.0) // unit: microsecond unsigned long cycle_time; unsigned long raising_edge; unsigned long falling_edge; unsigned long prev_micros; // compare 2 unsigned value // true if X > Y while for all possible (X, Y), X - Y < Z #define TIME_CMP(X, Y, Z) (((X) - (Y)) < (Z)) inline void setHigh() { // 2 CPU cycles to balance execution time with setLow() // this is based on measurement on Arduino UNO R3, your mileage may vary PORTB = B00100000; PORTB = B00100000; } inline void setLow() { PORTB = B00000000; } void setup() { DDRB = B00100000; prev_micros = micros(); while(1) { // read everything from analog input (potentiometer) // frequency: 0.1-102.4 Hz // width: 0-100% // offset: 0-100% //freq = (double)(analogRead(1) + 1) / 10; //width = (double)(analogRead(0) + 1) / 1024; //offset = (double)analogRead(2) / 1024; // OR manual settings // max possible frequency is around 55000Hz with <1KHz deviation // based on measurements on Arduino UNO R3 // you may get to ~77500Hz with significantly larger deviation // note: please uncomment the next 3 expressions, then // move the following 6 expressions ahead of while loop // if you are going to use manual settings, because it is no worth // to recalculate them. freq = 50; width = 0.3; offset = 0.0; cycle_time = 1000000 / freq; raising_edge = (unsigned long)(offset * cycle_time) % cycle_time; falling_edge = (unsigned long)((offset + width) * cycle_time) % cycle_time; if (width + offset < 1) { // raising edge should appear earlier while (TIME_CMP(micros(), prev_micros + raising_edge, cycle_time)); setHigh(); while (TIME_CMP(micros(), prev_micros + falling_edge, cycle_time)); setLow(); } else { // falling edge should appear earlier while (TIME_CMP(micros(), prev_micros + falling_edge, cycle_time)); setLow(); while (TIME_CMP(micros(), prev_micros + raising_edge, cycle_time)); setHigh(); }pin prev_micros += cycle_time; } } 解释： ...