Using mbed with external input

Page last updated 18 Nov 2010, by analog match. 0 replies

Progressed to using mbed to accept an external stimulus to control brightness of the led. The stimulus was a simple voltage applied from a 1.5V batt. connected to a 5K pot. But this is the first step to using the mbed for more complex control in a closed loop system to generate a PWM signal. The code is unbelievably simple:

#include "mbed.h"

AnalogIn ain(p20);
PwmOut led(LED1);

int main() {

 while(1){
        //read the value of pin 20 as a percentage of max voltage which is 3.3V. 
 //so 0V->0.0%
 //   1V->30.3%
 //   1.5V->45.45%
 float varf = ain.read();

 //use the %age of voltage value read in as the setting for
 //output of PWM.
 led = varf;

 wait_ms(0.01);
 }

} //main

Next experiment is to light up other leds as the voltage is increased.

11/18/10:

Made further improvements to my simple PWM program controllable by a pot. Set the lower limit of duty-cycle to 10% so that I don't go to zero D. Tested this out by printing actual analog value at the pin and the value passed to LED1.

Next steps:

Format the data going to tera term a bit more nicely.

Figure out a way to stop the system when the reset button is pressed. This will need some understanding of interrupts.

Apply this PWM output to drive a FET using a gate driver.

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