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melegaunt
Joined: 10 Apr 2013
Posts: 1
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| Need help with ADC and quadrature encoder code |
 Posted: Wed Apr 10, 2013 3:06 pm |
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Hi I have a project I'm working which requires very low frequency <1hz.
I have two photosensors which output analog into the input pins of a 16f1937 and these sensors will be controlling the motor I have. I have an Hbridge controlling the motor.
I have limited knowledge of C and CCS, and all the examples of ADC I've found are for much higher frequencies, so I'm not sure how to approach using such a low frequency.
For the encoder I was thinking about using this code posted by Ttelmah and modifying it to my needs. But I need to solve the ADC problem first.
| Code: | signed int32 position;
#INT_RB
void quad(void) {
static int old;
static int new;
static int value;
//Here I have an edge on one of the quadrature inputs
new=portb;
/*Now I have to decode the quadrature changes. There are four
possibilities:
I can have a rising or falling edge, on each of the two inputs. I have to
look at the state of the other bit, and increment/decrement according to
this. /*
value=new^old;
//'value', now has the bit set, which has changed
if (value & 0x10) {
//Here the low bit has changed
if (new & 0x10) {
//Here a rising edge on A
if (new & 0x20) --position;
else ++position;
}
else {
//Here a falling edge on A
if (new & 0x20) ++position;
else --position;
}
}
else {
//Here the high bit (B) must have changed
if (new & 0x20) {
//Here a rising edge on B
if (new & 0x10) ++position;
else --position;
}
else {
//Here a falling edge on B
if (new & 0x10) --position;
else ++position;
}
}
old=new;
} |
My project is basically a baby swing but for adults. So I need the encoder to change the direction of the motor after a certain distance is traveled.
I think this program determines the direction the motor is spinning by looking at the sign of position(??). I was thinking of adding interrupts to check the value of position and changing the direction if position is above a certain value. |
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bkamen
Joined: 07 Jan 2004
Posts: 1611
Location: Central Illinois, USA
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| Posted: Wed Apr 10, 2013 7:19 pm |
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You can always set the ADC to sample as slow as you want.
Just because it takes some number of microseconds to get the sample doesn't mean you have to sample as fast as it can between samples.
I've written apps that sample once a minute.
Your code doesn't reflect anything that does A/D sampling but rather only a portB interrupt routine.
Remember to read the PIC101 Sticky at the top of this forum.
Cheers,
-Ben
_________________
Dazed and confused? I don't think so. Just "plain lost" will do. :D |
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