10 years, 8 months ago.

mbed NXP LPC1768: questions about using of AnalogIn and AnalogOut

Hello everybody,

I want to buy the mbed NXP LPC1768 in order to use it for a specific application. In short, I need to read an analogic voltage ("setpoint" ==> see just below), to treat it and after to write an analogic output voltage ("temp" ==> see just below). The body of the code is the following:

1. include "mbed.h"
2. include <AnalogIn.h>
3. include <AnalogOut.h>

void Init(); void Application();

float setpoint, temp, setpoint_in, temp_out; + other variables

*************** Main() - Main Routine *************** void main() { Init(); Initialize the mbed NXP LPC1768

while(1) Loop Forever {Application();} }

*************** Init - Initialization Routine *************** void Init() { AnalogIn setpoint_in(p15); AnalogOut temp_out(p18); + initialization of other stuff return; } void PID() { setpoint = setpoint_in.read(); + computation using "setpoint" in order to calcul "temp" temp_out=write(temp); return; }

My questions are the following:

- what are the impedances of analogic input and output I'm using of the card mbed NXP LPC1768 ?

- Are AnalogIn.h and AnalogIn.h compatible with the card I want to use? I took this from:

• http://mbed.org/users/mbed_official/code/mbed/docs/9c8f0e3462fb/classmbed_1_1AnalogIn.html
• http://mbed.org/users/mbed_official/code/mbed/docs/9c8f0e3462fb/classmbed_1_1AnalogOut.html

- If it's compatible, I saw something strange: it's written on the websites just above that the functons read() and write() convert the signal with 16 bits of precision, but ADC of the card is 12 bits precision and DAC is 10 bits precision, so I don't understand why it's possible to obtain 16 bits precision using the functions read() and write() ?

- For the specific task I want to achieve, the output voltage "tmp_out" need to be filtered with an integrator followed by a low pass filter of second order. I suppose that "temp_out=write(temp);" take the digital signal "temp" and convert it into the analogic signal "temp_out" with the DAC of the card, without any filtering after the DAC? If it's like that, is it possible with the card itself to put an integrator followed by a low pass filter of second order, or do I have to construct these things by myself with electronic components and put them after the output of the card?

Thank you very much in advance for your answer,

Quentin