Encoder selection to use with NI PCI 6221 for an Inverted Pendulum Project

[Plínio]

Hello Geank,

The RS422 output is not compatible with NI PCI 6221. This is a serial protocol and it is not read by the device counters input.

http://www.ti.com/lit/an/slla070d/slla070d.pdf

As you can see on the link bellow, you can use three possible output types (Line Driver, Open Collector and Push-Pull), but the recommended choice is Push-pull output because the M Series

card works best when it is constantly driven.

http://digital.ni.com/public.nsf/allkb/0C5091E9099059BC86256FC1007947AA

Feel free to contact us again if you need

Plínio Costa

Application Engineering

National Instruments Brazil

[Geank]

Thanks Plínio, well definetely RS422 encoders are rejected now, but what about the TTL/74LS04 output type inc. encoders? I read a robotic arm project that used the same card I'm using and it seems to be that it had inc. encoders with TTL output signals, a signal which by the way the 6221 appears to manage. If they work too, could I be able to connect them as a normal pull-push encoder, using the same pins assigned for an inc. enc. as appears on a previous post I made in this thread -image included-? would it be any problem with the counters?

Here´s a snapshot of the characteristics (is the second column CP-850/950):

Regards.

Geancarlos

[Plínio · Accepted solution]

Hello Geank

First of all, I apologize for the wrong information I've wrote previously

I was searching for more information about RS422 and I realised that maybe this is a possible solution

https://www.national.com/ds/DS/DS9638.pdf

http://www.photocraftencoders.com/Incremental%20Encoder%20Options%20&%20Features.htm
(check the Differential Line Driver (RS422) topic)

http://www.dynapar.com/uploadedFiles/_Site_Root/Technology/White_Papers/Selecting%20the%20Right%20En...
(check the Line Driver topic)

As you see on the links above, RS422 is a push-pull output (line driver used in a single-ended format).

About your second choice, it is a possible solution as well since you ensure a correct supply (TTL compatible, as I see it's your case).

Although all those researches led me to those conclusions, I advice you to talk to your transducer vendor to be sure about the compatibility. For sure they can clarify better all your current and future doubts about encoder outputs types.

PCI 6221 Specification (Datasheet)

http://www.ni.com/pdf/manuals/371290g.pdf

http://sine.ni.com/ds/app/doc/p/id/ds-15/lang/pt

Regards

Plínio Costa

Application Engineering

National Instruments Brazil