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Please, help me with making hysteresis!

 
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40inD



Joined: 30 Jul 2007
Posts: 112
Location: Moscow, Russia

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Please, help me with making hysteresis!
PostPosted: Wed Aug 01, 2007 6:01 am     Reply with quote
I need to implement hysteresis in termoregulator device. I have desired temp (Td), current temp (Tc) and Delta Td (hysteresis).
libor



Joined: 14 Dec 2004
Posts: 288
Location: Hungary

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PostPosted: Wed Aug 01, 2007 9:46 am     Reply with quote
Do you read current temp as an analog input using the A/D ? I suppose you want the hysteresis done in software, and you are controlling a digital port.
You can define the two levels for the switching and use the according level depending on the current state (ON or OFF) of the state machine.
Code:
#define OFF 0
#define ON 1
int state;
...
lowerlimit=Td-delta;
upperlimit=Td+delta;
...
if (state == ON) {
  if (Tc>upperlimit)  {
  state = OFF;
  //... turn off heating
  }
}
if (state == OFF) {
  if (Tc<lowerlimit)  {
   state = ON;
  // ...turn on heating
  }
}


if you are controling an analogue output like a PWM output I would rather suggest to use a PID algorythm instead calculating the error and acting upon it.
40inD



Joined: 30 Jul 2007
Posts: 112
Location: Moscow, Russia

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PostPosted: Wed Aug 01, 2007 12:22 pm     Reply with quote
Idea Thanks! It works. Very Happy
(I use DS18B20, but it's no matter)
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