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Guest
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| Making hysteresis to A/D. |
 Posted: Fri Dec 19, 2008 9:11 am |
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Using 8 bit A/D 0-255, want to use a pot. as a selector.
I want 4 step and don't want toggling between the step, therefore I want to use some hysteresis maybe 5-10 count.
Step without hysteresis.
0-63 step 1
64-127 step2
128-191 step3
192-255 step4
How to make the smartest implementation? |
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libor
Joined: 14 Dec 2004
Posts: 288
Location: Hungary
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| Posted: Fri Dec 19, 2008 10:28 am |
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I would just insert some 'neutral zones' between the 'steps'.
0-59 valid step 1
60 - 67 neutral zone
68-123 valid step2
124-128 neutral zone
129-191 valid step3
...etc
a reading in any neutral zone would result a no-change in the 'step'. (the previous state remains selected) a simple sequence of if()... structures will do.
However upon power-on you should initialize the step to the closest valid range. |
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Guest
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| Posted: Fri Dec 19, 2008 11:01 am |
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Like this...
| Code: | void readad(){
const int8 hyst=5;
int8 res;
res=(int8)read_adc()&~0x03; //cutoff 2 bit
if (res>0 && res<42+hyst){} else
if (res>42-hyst && res<85+hyst){} else
if (res>85-hyst && res<127+hyst){} else
........
}
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RLScott
Joined: 10 Jul 2007
Posts: 465
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| Posted: Fri Dec 19, 2008 1:20 pm |
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| Anonymous wrote: | Like this...
| Code: | void readad(){
const int8 hyst=5;
int8 res;
res=(int8)read_adc()&~0x03; //cutoff 2 bit
if (res>0 && res<42+hyst){} else
if (res>42-hyst && res<85+hyst){} else
if (res>85-hyst && res<127+hyst){} else
........
}
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No, I'm afraid this code will not implement hysteresis. The first "if" guarantees that the second "if" will never see a value of res<47, so there is no point in looking for "res>42-5". To implement hystersis, there must be some form of static memory of the previous range you were in, such as the variable "Range" in the following:
| Code: |
void readad(){
const int8 hyst=5;
int8 res;
res=(int8)read_adc()&~0x03; //cutoff 2 bit
if (res<42-hyst) Range = 0;
else if(res<42+hyst) Range = (Range<1) ? 0 : 1;
else if(res<85-hyst) Range = 1;
else if(res<85+hyst) Range = (Range<2) ? 1 : 2;
else if(res<127-hyst) Range = 2;
else if(res<127+hyst) Range = (Range<3) ? 2 : 3;
. . . .
switch(Range)
{
case 0: {} break;
case 1: {} break;
case 2: {} break;
case 3: {} break;
. . . .
}
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_________________
Robert Scott
Real-Time Specialties
Embedded Systems Consulting |
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Guest
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| Posted: Sat Dec 20, 2008 2:47 pm |
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| Nice code, thanks :-) |
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