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Legacy Personal Blogs TI Hercules LaunchPad Type 1:  Heart Emulator
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  • Author Author: martinvalencia
  • Date Created: 18 Mar 2015 8:58 PM Date Created
  • Views 551 views
  • Likes 0 likes
  • Comments 0 comments
  • hercules_launchpad
  • n2het
  • digital
  • to
  • opamp
  • converter
  • library
  • het
  • nhet
  • low
  • rm42x
  • noise
  • adc
  • launchpad
  • analog
Related
Recommended

TI Hercules LaunchPad Type 1:  Heart Emulator

martinvalencia
martinvalencia
18 Mar 2015

Pulse Width Modulation (PWM) modules, which produce basically digital waveforms, can be used as cheap Digital-to-Analog (D/A) converters only a few external components.

A wide variety of microcontroller applications exist that need analog output but do not require high resolution D/A converters.

Conversion of PWM waveforms to analog signals involves the use of analog low-pass filters

In a typical PWM signal, the base frequency is fixed, but the pulse width is a variable. The pulse width is directly proportional to the amplitude of the original unmodulated signal. In other words, in a PWM signal, the frequency of the waveform is a constant while the duty cycle varies (from 0% to 100%) according to the amplitude of the original signal.

for calculating the low-pass filter, you first must know the bandwidth of the signal to be reconstructed.

image

And the bandwidth can be calculated frequency PWM for our application, clearly applying a multiplier K factor, while K >> 1, the resolution of the signal is greatly improved, but also must consider the resolution of the PWM Dutty.

image

PWM frequency with already established, it can proceed to design the low-pass filter, with the following equation.

imagehttp://e2e.ti.com/cfs-file.ashx/__key/communityserver-discussions-components-files/312/8510.forumla1.png

must be added to the output of OPAMP pass filter to provide a low impedance and good power delivery to the application.

image

Cardiac result signal generated by the PWM

image

NOTA: As can be seen the signal has a significant quality reconstructed, but has a curl, these are achieved by increasing the degree of eliminating pass filter

Heart Singal mode duty cycle

int dac[]={43,44,46,46,47,48,50,52,53,53,57,59,62,62,67,68,71,72,76,79,81,81,

85,86,89,89,90,92,93,92,93,93,94,91,91,91,90,90,87,87,86,84,82,81,

80,79,76,76,73,72,69,69,68,67,64,64,62,61,59,58,57,56,55,53,53,52,

50,49,50,48,48,46,47,45,45,43,43,44,43,40,41,41,41,39,40,40,39,39,

39,39,40,38,37,38,37,38,37,39,39,38,37,39,39,40,38,40,40,40,39,40,

41,40,39,41,41,42,41,41,43,42,43,42,43,44,43,42,43,44,44,43,45,43,

45,43,45,46,46,44,45,45,46,43,45,46,45,45,46,47,48,46,46,47,47,47,

46,47,47,46,45,46,47,47,45,47,47,48,46,47,48,48,46,47,48,49,47,48,

48,49,49,49,50,51,49,49,49,49,49,48,50,50,49,48,50,52,51,50,51,51,

52,49,49,49,48,47,47,47,48,45,45,47,47,47,45,47,47,47,46,47,48,48,

46,49,48,50,48,49,50,49,49,49,50,50,49,49,50,50,50,49,50,51,51,49,

49,47,46,41,38,33,28,22,19,19,20,23,30,37,47,55,63,74,81,85,86,89,

90,88,88,86,82,80,77,73,68,63,58,54,51,47,41,40,38,37,34,35,35,35,

33,34,35,36,34,35,36,36,37,36,38,40,39,38,39,40,41,39,42,41,42,40,

42,43,43,42,44,43,45,43,44,45,45,45,45,46,47,44,45,46,46,46,45,47,

47,46,45,46,46,46,44,45,44,46,43,43,45,45,42,43,43,44,41,41,42,42,

42,40,41,42,40,40,41,41,42,41,43,43,44,43,45,47,47,47,49};

 

Code / C++:

while(1){

for(i=0;i<=370;i++)
{
pwmSetDuty(hetRAM1,pwm6,dac[i]);
wait_secons(2e-3); // delay 2ms
}
}

Video Cardiac emulator

                                                                 

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