topic Re: Quadrature Decoding in LabVIEW

Quadrature Decoding

Ambrose1464 — Wed, 27 Jul 2016 03:26:53 GMT

Currently I'm have problem for the comparison signal A and B. From the vi below I'm using the feedback node to check the previous iteration(PI) and current iteration(CI) for signal A, if PI higher than CI it the signal will detect as falling edge and if PI lower than CI will detect as rising edge. So how I'm going to build an algorithm to detect whether the signal A lead B (detect as rising edge and is up counter) or the signal B lead A (detect as falling edge and is down counter)?

Re: Quadrature Decoding

GerdW — Wed, 27 Jul 2016 06:24:47 GMT

Hi Ambrose,

you just need to check PI/CI of A and B signal as shown in these tables…

Re: Quadrature Decoding

Ambrose1464 — Wed, 27 Jul 2016 08:08:45 GMT

@GerdW wrote:
Hi Ambrose,

you just need to check PI/CI of A and B signal as shown in these tables…

I know to generate signal, but problem is how to know whether the signal is A lead B (then the counter will count up) or B lead A (then counter will count down)?

Re: Quadrature Decoding

GerdW — Wed, 27 Jul 2016 09:12:11 GMT

Hi Ambrose,

those tables explain how to determine direction!

Examples:

When PI for AB is 00 and CI is 01 then you have a clockwise rotation/forward movement.

When PI is 11 and CI is 01 you see counter-clockwise rotation/backward movement…

You already know how to compare PI/CI for a single signal (either A or B), so what's the problem to compare the same for a combination of AB?

Re: Quadrature Decoding

Ambrose1464 — Wed, 27 Jul 2016 09:25:48 GMT

@GerdW wrote:
Hi Ambrose,

those tables explain how to determine direction!
Examples:
When PI for AB is 00 and CI is 01 then you have a clockwise rotation/forward movement.
When PI is 11 and CI is 01 you see counter-clockwise rotation/backward movement…

You already know how to compare PI/CI for a single signal (either A or B), so what's the problem to compare the same for a combination of AB?

Here is the signal i generated (pic below)

my problem is how to detect the rising or falling edge for the both channel A and B ?

Re: Quadrature Decoding

GerdW — Wed, 27 Jul 2016 09:33:25 GMT

Hi Ambrose,

in your first message you already described the algorithm: compare PI and CI of the signals…

You need a shift register and a comparison function!

(Or you try the PtByPt-BooleanCrossing function available in LabVIEW…)

Re: Quadrature Decoding

Ambrose1464 — Wed, 27 Jul 2016 10:12:08 GMT

@GerdW wrote:
Hi Ambrose,

in your first message you already described the algorithm: compare PI and CI of the signals…
You need a shift register and a comparison function!
(Or you try the PtByPt-BooleanCrossing function available in LabVIEW…)

Mind you share out the vi how is it look like? I try so many way still not achieve. T.T

Re: Quadrature Decoding

GerdW — Wed, 27 Jul 2016 11:07:27 GMT

Hi Ambrose,

what have you tried so far?

Two solutions, both mentioned before:

Re: Quadrature Decoding

Ambrose1464 — Wed, 27 Jul 2016 11:51:52 GMT

@GerdW wrote:
Hi Ambrose,
what have you tried so far?
Two solutions, both mentioned before:

Thank you for your showing vi. What I want is detect if A lead B then each of the rising edge of the channel A the counter will count up and if B lead A then each of the falling edge of the channel B the counter will count down. This is what I finally want. I can generate the signal A and B but I dunno how to detect and compare the signal only. Thank you.

Re: Quadrature Decoding

GerdW — Wed, 27 Jul 2016 12:24:06 GMT

Hi Ambrose,

did you read the Wikipedia article I linked above? Did you understand the part explaining AB/Quadrature encoders with rotary encoders as example?

You need to get the current state of A and B and compare them with their previous state. The tables show you the possible combinations and their meaning (forward/backward movement).

Comparing boolean signals is easy - as shown above. Comparing numeric values is also easy using simple comparision functions!

Re: Quadrature Decoding

Ambrose1464 — Wed, 27 Jul 2016 13:00:52 GMT

@GerdW wrote:
Hi Ambrose,

did you read the Wikipedia article I linked above? Did you understand the part explaining AB/Quadrature encoders with rotary encoders as example?

You need to get the current state of A and B and compare them with their previous state. The tables show you the possible combinations and their meaning (forward/backward movement).
Comparing boolean signals is easy - as shown above. Comparing numeric values is also easy using simple comparision functions!

Here is my vi. I tested already. but the counter din get correct way. If in A lead B mode every rising edge of channel A the counter will count up and if B lead A mode every falling edge of the channel A counter will count down. I testing so many time i still cant get it.

Re: Quadrature Decoding

GerdW — Wed, 27 Jul 2016 13:11:07 GMT

Right now I'm limited to LV2014. Can you attach a downconverted version of your VI?

If in A lead B mode every rising edge of channel A the counter will count up and if B lead A mode every falling edge of the channel A counter will count down.

You need to attack the problem from the other side (as shown on Wikipedia): you check the current state of A and B and compare with their previous states to decide between "A leads B" or "B leads A" (count up/down)!

Re: Quadrature Decoding

Ambrose1464 — Wed, 27 Jul 2016 13:34:03 GMT

@GerdW wrote:
Right now I'm limited to LV2014. Can you attach a downconverted version of your VI?

If in A lead B mode every rising edge of channel A the counter will count up and if B lead A mode every falling edge of the channel A counter will count down.
You need to attack the problem from the other side (as shown on Wikipedia): you check the current state of A and B and compare with their previous states to decide between "A leads B" or "B leads A" (count up/down)!

Here the vi i downconverted to Labview 2014. Thank you so much.

Re: Quadrature Decoding

GerdW — Wed, 27 Jul 2016 14:05:52 GMT

Hi Ambrose,

see this:

Re: Quadrature Decoding

Ambrose1464 — Wed, 27 Jul 2016 14:16:31 GMT

@GerdW wrote:
Hi Ambrose,
see this:

I still confusing what you mean PI=3 and CI=2 then count down??? the control a and b is it same as my vi after first case structure output a and b?

Re: Quadrature Decoding

Ambrose1464 — Wed, 27 Jul 2016 15:30:50 GMT

@GerdW wrote:
Hi Ambrose,
see this:

Hi GerdW, Thank you so much for your helping a lot. Finally I understand what you say PI=3 and CI=2. I get the result I want d. I'm appreciated it.

Comparison

Ambrose1464 — Thu, 28 Jul 2016 07:10:12 GMT

How i going to compare the A lead B and B lead A ? If A lead B will go to rising edge case then counter count up and B lead A will go to falling edge case then counter count down. Here is my vi below. Once I build thealgorithm the counter will count up and down together.

Re: Comparison

GerdW — Thu, 28 Jul 2016 07:27:38 GMT

Hi Ambrose,

yesterday you got the result, today you ask again?

And why did you create a new thread on the same topic? Please stick with one thread per problem…

You don't need to check for rising/falling edges. All you need to compare is state of AB with their previous state!

Re: Comparison

Ambrose1464 — Thu, 28 Jul 2016 08:19:16 GMT

According my vi, i directly make it true or false (mode control) statement for comparison, i found that did not compare the signal A and B by itself. That why I ask again.

Re: Comparison

GerdW — Thu, 28 Jul 2016 08:29:53 GMT

It's again a LV2015 VI. Please upload a downconverted version…