Pull a stepper pulse input low (ground) with a 9472 or 9381

[NXTenergy]

I have a stepper motor controller that requires a pulse output from my cRIO. The input for the pulse is tied high with a 20k ohm resistor on the driver and the rising edge of the pulse will cause it to actuate.

Essentially, I need an output that opens and closes a contact,  rather than the sourcing output on the 9472 or the 3.3V TTL on the 9381. Can either of these cards handle that?

I'm able to get the driver to operate using a sourcing output (from 9472) into a mechanical relay but that isn't ideal for several reasons.

Running LV 2014 with a cRIO 9073 in scan mode. The 1ms scan rate isn't a problem for the speeds we are looking for out of this motor.

[Kelle]

Essentially, I need an output that opens and closes a contact,  rather than the sourcing output on the 9472 or the 3.3V TTL on the 9381. Can either of these cards handle that?

I'm able to get the driver to operate using a sourcing output (from 9472) into a mechanical relay but that isn't ideal for several reasons.

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What are you actually looking for?  It sounds like what you want is a relay since you already have lines for your power.  Have you looked at the NI 9482 and NI 9485?  They are both relay modules, so you will get functionality of your relays without extra hardware.

I am a bit curious as to why the 9472 is not able to work for your stepper controller.  What are the necessary inputs for your stepper controller?  Are you creating your own drive and using the cRIO as the controller?

[Buechsenschuetz · Accepted solution]

A relay would not be suitable for creating stepper motor driver input signals. Even if it can handle the puls rate (but usually it is much higher than relays could handle) relays always have contact bouncing which would disturb operation of the stepper driver. 

A simple npn transistor circuit will do the job. Connect emitter to GND, base via something between 10kOhm and 47kOhm to the card output and collector to the input of the stepper driver. 

[NXTenergy]

Thanks Buechsenschuetz, 

I am currently making do with a mechanical relay because I'm controlling the stepper fairly slowly, but this isn't, as you say, a good solution.

Not being an EE (and as an ME hating that class), I'm not terribly  familiar with the npn circuit to which you refer. If you could point me to documentation that would be fantastic. Alternatively, to a product on the market that will take my digital output and deliver a signal that pulls to ground. 

Right now I can sucessfully use a Red Lion AFCM0000 ANALOG TO FREQUENCY converter but I'm not looking for proportional output because I need to actuate the stepper a specific amount of steps. 

[NXTenergy]

Kelle, 

Those relay modules don't output fast enough, unfortunately. 

I'm tying into the driver for a Clippard stepper controlled needle valve (http://www.clippard.com/products/electronic-valve-proportional#scpv).

What I need to do is give the driver a pulse input (typical of a stepper driver) but that input is tied high with a 20k ohm resistor meaning the pulse needs to pull it down (to ground) which is not something that I've been able to accomplish with a 9427. 

[Kelle]

to run with the NPN transistor idea, here is a good link: https://learn.sparkfun.com/tutorials/transistors/applications-i-switches
the idea is to use the output of a DO card, that can switch much faster than a relay, to act as a switch, doing the same thing as what the relay was doing, but with transistors

[NXTenergy]

Following up on this, I got it to work after a fashion: If I disconnected the stepper driver from the ground (in the attached figure the ground is shown connected as I think it should be) the transistor switch worked. As shown, it wouldn't. 

R1= 30k Ohm

R2 (you didn't mention that I should put one there so I didn't

R3= 20k Ohm

The problem is that each time I turn the DO "ON" the stepper driver actuates multiple times--sometimes the wrong way like it's bouncing--till I turn it "OFF" whereas I need it to just actuate once for every "ON/OFF" cycle. 

You may notice I'm using a 5VDC output. Tomorrow I'll go try it with the cRIO at 24VDC on the output. 

Thoughts?

[NXTenergy]

Update: 

Using the output of the 9472 (24VDC) connected to the base through 10-47k Ohm using a decade resistance box I was NOT able to get it to work.

Collector connectected directly to the step input of the driver.

Emitter connected to the common ground (for both controller and power supply).

Using a PN2222A transistor, btw.  

[NXTenergy · Accepted solution]

The circuit diagram finally got through to me. The problem was that I was connecting the emitter to the earth ground but all it wanted was to be connected with the ground on the driver (see the diagram). 

Works fine now. I tried with resistances from 10-50k Ohm with fair results. Thanks!