Master project, Make a plate vibrate according to the Co2 level

Projects Discussion and Showcase Interactive Art
9 
  return ppm_pwm;


    if ("PPM UART" > 1400 )  digitalWrite (ledpin , HIGH);
    if ("PPM UART" < 1400 )  digitalWrite (ledpin , LOW);
}

.Code after an unconditional return is never executed, so there is little point on having that nonsense there.
Comparing a string literal to a numeric literal makes very little sense

What is the problem with your code?

Acceptable answers do not include "it doesn't work"