Quadrature decoder

tepper motors

ers.

-Lasse

motors

Work statement too vague :-)

What _exactly_ are you looking for? A _detector_ that produces a pulse train _and_ direction? ...Jim Thompson

I was snooping around Google Groups. Thanks.

I'll look over the diagram. Here is what i have been looking at......

greg

Right, pulse and direction.

greg

I also found this. All I would need is a separate toggle switch to choose direction, but not so cool......

If you only care about speed and not direction, one edge on one channel m= ay be sufficient.

greg

Like this...

I've seen self-clocking versions.... found this...

But I've seen it done with a dual-D, but it escapes me right now :-0 ...Jim Thompson

Its been a long project. i tried to get an existing controller to work with my steppers. For a Z axis motion. I thought i needed more power so I used two audio amps to act as buffers from the stepper output. That did not help much. i didn't figure out why the motors did not like the drive output. So now I am wiring a separate Z axis system, which is a lot simpler than using the existing system. The movement is by knobs, and the speed will not be over 500 Hz. I also did not want to drive two steppers in sync, but thats what I was given. I could have also ordered an opto knob with step and direction outputs but its a time thing right now.

greg

If one phase clocks a D-flop which has as "D" the other phase, you get a direction signal.

Pulses is pulses is pulses ;-) Maybe XOR the two phase for fun ?:-) ...Jim Thompson

Missed the diagrams, I was looking at earlier today.

My first thought, simple, and perhaps even better, was to use just a toggle switch. I thought about using a VCO that would speed up the longer you hold the toggle up or down. You go up, and you go down. Not as precise though as in focusing a microscope.

greg

stepper motors

That can be done with a 7474 (dual Data flip flp).

I'm not going to get into details but, you do need to invert the CLK signal for each FF in the package.. Basically:

Channel A drives FF #2's Data and Clr pin while it also drives the inverted circuit for the CLK of FF #1

Channel B drives FF #1's data and clr pin while it also drives the inverted circuit for the CLK for FF #2

Net results are:

FF #1 outputs CW pulses while FF #2 outputs CCW pulses..

Using a basic NPN common emitter type inverting circuit for the CLK with a pull up R, should work just fine.. I guess one could also use a pre biased transistor..

P.S. Most encoders use a open collector scheme. You'll need to supply a pull-up or use a PNP inverting circuit which would remove the need of the pull up of the encoder line.. You would still need a pull down R on the inputs of the CLK I guess..

ot

rollers.

for most things that is a terrible way of doing it, a slight mechanical mechanical vibration or electrical noise that gets into the channel you use for pulses, will looks just like it constantly moving in one direction

do it the right way and it will just toggle back and fourth

-Lasse

controllers.

Really, I've never seen that. I use a dual D-ff, the other Channel holds the Data and CLr pin to one state. Even if lets say channel A is chattering, channel B is in the middle of the phase supplying the DATA pin for the state which isn't moving.

Oh well, maybe we have different circuits..

tepper motors

The controller converts that 'step and direction' into quadrature when it drives the motor. Are you SURE it requires step/direction, there's no other options?

True quadrature is a four-state counter, and only transitions to adjacent states are 'known-direction' transitions. In other words, 0=3D>1 is an up count, 0=3D>3 is a down count... and 0=3D>2 is indecipherable. You have to decide how your decoder should misbehave in that case...

controllers.

You only get the direction once per "cycle". The four flip-flop (two two-bit shift registers) and XOR solution updates every quarter cycle and is more stable around edges.

tepper motors

ers.

If you are planning to use the quad decoder to feed into the stepper motor controller why not just beef up the output drive of your quadrature knob and drive the motor directly? regards, al

Well, I liked the idea of having current control, and I allready had one channel wired up. I DO have a driver chip that will do what you said. I am going to consider it for simplicity. Darn stepper is only 3.3 ohoms.

greg

stepper motors

The problem with all clocked or sampled quadrature decoded such as those referenced above is transition jitter. I know this from personal experience where such a detector on a mechanical system was subject to vibrations that could occasional cause a rapid set of transition forward&backwards some of which would be missed by a clocked system. This leads to false counts.

Cheers

ian