How to get encoder direction and speed / rpm ? ( with DT INT ?)

[HenrikOlsson]

Oh, in that case there's no need for the 18F2431, it would be overkill.
Set one of the PICs timers up as a counter and feed the pulses from one channel to it, then read its value at precise intervals and you have the velocity. Or use the Count command to Count pulses for a certian amount of time. Or, instead of counting pulses, use the capture module to measure the length of ONE pulse. Or use PulsIn to do the same thing, or.....

/Henrik.

[luminas]

Hahaha, yes indeed 18F2431 would be overkill

Okay, the issue with rpm is clearer now, but what about direction ?

[HenrikOlsson]

Like I said earlier, read the state of channel B at the rising edge of channel A and you have the direction.

[luminas]

Like I said earlier, read the state of channel B at the rising edge of channel A and you have the direction.

i am not quite clear about it, is it something like this ? :

porta =00000001 direction is clockwise
porta =00000010 direction is counter clockwise

what happen with the direction WHILE the encoder is rotating ? wouldn't it be changing constantly ?

[HenrikOlsson]

The two signals are 90 degrees out of phase in relation to each other. This is what it looks like:

When the encoder is rotating "forward" (ie you're going left to right in the above picture) channel B is low at the rising edge of channel A. When the encoder is rotating "backwards" (ie you're going right to left in the above picture) channel B is high at the rising edge of channel A. So, you need to detect when channel A goes from low to high and then read channel B.

WHILE ChannelA_Input = 1 : WEND   ' Wait for channel A to go low if it happens to be high
WHILE ChannelA_Input = 0 : WEND   ' Now wait for the rising edge of channel A
Direction = ChannelB_Input           ' If channel B is high we're moving in one direction, if it's low we're moving in the other

The above code obviosuly presents a risk of hanging if the velocity happens to be 0 or very low but you get the idea.

/Henrik.

[luminas]

The above code obviosuly presents a risk of hanging if the velocity happens to be 0 or very low but you get the idea.

I thought about that , but I worried about DT-INT would block it in the process

is it possible to put this in-line with speed detecting process ?

[luminas]

I can find direction with this code:

A tied to portb.4
B tied to portb.5

Direction = portb.5 ^ portb.4
lcdout $FE,1,DEC(Direction)


but, the reading is NOT consistent , if I turn clockwise , Direction is not always 1 ( well , most of the time it is 1 ) and vice versa

any tips anyone ?