UMI 7772 voltage limit?

[steffi.kono]

Hi,

does anybody know if the UMI 7772 releases voltage under 5V?

I tried to run a stepper motor wit the UMI 7772 (with MAX). There is no error at MAX, Axis is moving, no LEDs are red, but the motor isn't moving?! So my only idea is that the voltage released from the UMI Axis is beneath 5V (because the motor needs 5V at least). I connected the motor to the step signal and digital ground of the control connector of the UMI Axis. Are there other possibilities? Can I set the voltage release to 5V anywhere?

Thanks a lot.

Steffi Kono

[Jochen]

The step and direction signals provided by the UMI-7772 are pass-through signals from your motion control board. Both signals are driven by an open-collector output that is pulled up with a 3.3 kOhm resistor to +5 V internally. If you see a voltage drop for these lines, your amplifier has probably a quite low input impedance, which pulls down the voltages by some amount.

To overcome this problem you should connect another resistor from the step/dir outputs to the +5V output (pin 3) inside your axis control connector. The step and direction outputs can sink up to 64 mA. That means that your pull-up resistor can be as low as about 80 Ohms but as you shouldn't go too much to the limit I would recommend to use a 200 Ohm resistor.

For more information about the output circuitries of your motion control board please refer to the appropriate manual.

I hope this helps,

Jochen Klier
National Instruments Germany

Message Edited by Jochen on 05-02-2007 12:04 PM

[Brian_Beal]

I am reading his message as there is no amplifier.  A drive(amplifier) is needed between the motion controller and the stepper motor.

[Jochen]

Telling from Steffi's other threads, I'm pretty sure that there is an amplifier used here

Jochen

[AnalogKid2DigitalMan]

Steffi:

I saw your other posts regarding the ECMD275, here's the manual:

http://www.ec-motion.com/pdl/Handb_ECMD275_e.pdf

NOTE: this driver comes in various versions- one accepts 5V inputs for step and direction, the other accepts 24V. Please check your version and reference the manual.

-AK2DM

[Buechsenschuetz]

I just checked the manual briefly, and it is stated that also in the 5V input version optocouplers are used.

Optocouplers usually need several milli-amps to drive the input LED. Some work with 3mA, some need 5mA, virtually all will work with 10mA input current.

The TTL output of the UMI/NI board will be current limited by the 3.3kOhm pull-up resistor. With the load of an optocoupler, the output voltage will break down to the forward voltage of the input LED which probably is around 1.0V at the given current limit.

To drive optocouplers, it is better to use the outputs of the NI boards/UMI in "sink mode". Connect a +5V source to the (+) terminal of the driver input in question, and connect the (-) terminal to the output of the NI board. The power supply must have common GND (DGND) with the NI board. In sink mode, the outputs can drive up to 24mA which is more than sufficient for all optocoupler inputs.

Note that the logic level of the outputs is reversed. You should set them to "active low" mode. I.e., if you write a 0 into a given output, the output transistor will switch on. In source mode, the voltage across the output resistor would break down, thus yielding a TTL low level. In sink mode, current will flow from the +5V source through the optocoupler and activate it. This is not very important for the STEP output, but for the DIR output this is VERY important - direction of movement will be reversed if you use sink mode instead of source (TTL output) mode.

[Buechsenschuetz]

Having taken a closer look at the manual of your driver, I found that there are wiring schematics for the control interface provided. For connection with UMI/NI motion boards you should refer to the first and third schematic on p.5 (signal active low).

[steffi.kono]

Hi all:

thanks to everybody! I have worked on another project last couple weeks, that why I'm late with my response. Sorry! I just want to make sure that I got you right:

I should connect (+PULS) of the amplifier with (+) of the additional 5V source, (-PULS) of the amplifier with Step (CW) (Pin 4 of control connector) of UMI, (-) (Digital Ground. e.g. pin 10?) of UMI with (-) of 5V source. Is that right?

And should I do the same with the direction output? Do I need a second 5V source then? Or can I use the same?

Thank you sooo much!

Steffi

[Buechsenschuetz]

As far as I can tell from the distance your set-up seems OK.

No, you do not need a second +5VDC source to feed the DIR input. You can connect DIR+ to the same +5VDC source as STEP+, i.e. both terminals can be connected to the same +5VDC source.

Make sure that the +5VDC source is properly regulated. The NI boards (and I think the UMI box, too) have overvoltage protection at their outputs - but the excess voltage will be fed into the supply circuit which may have fatal consequences.

[steffi.kono]

Sorry, one more question...:

Where can I set the UMI to sink mode (in MAX)? Or is it automatic in this mode when I wired it to the 5V source and set the logic levels of the outputs to active low?

Thank you...