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driving a steppermotordriver-board which has a paralleport-interface — Parallax Forums

driving a steppermotordriver-board which has a paralleport-interface

StefanL38StefanL38 Posts: 2,292
edited 2012-12-15 17:20 in General Discussion
Hi,

I bought a steppermotordriver-board which has a parallelport interface. (short PPI)
I want to connect it to the propeller-chip. I tested the PPI by hand. it works only properly when driven with 5V.
The PPI of the stepperdriverboard has pullup-resistors that are pulling the step/dir inputs to 5V.
Then I tested if simple current-limiting resistors PPI----resistor----Propellerchip-IO-Pin. This does not work.

So I inserted a 74ACT244 to protect the propeller-chip against the 5V.


Propeller-IO-Pin
>>
Input-of-74ACT244-->>--Output-of-74ACT244
>>
PPI-Input.

This configuration works not reliable. As soon as I touch the wiring at the point with "X"
the signal gets disturbed so much that the steppermotor stalls.

Propeller-IO-Pin
X---->>
Input-of-74ACT244
>>
Output-of-74ACT244
>>
PPI-Input.

What can I do to improve this interface to work reliable?
Should I add a Pullup-resistor or pulldown-resistor at the point with the "X". And if yes what resistance should I use?


Would optocouplers be a better choice?
(BY THE WAY the stepperdriver-board has optocouplers but the manufacturer of the board was crazy enough
to supply both sides (of the optocouplers ) of the board from the 24V input. Which means there is a 5V regulator for the PPI
but it is supplied from the 24V steppermotor-power-input.

The board uses the TB6560-stepperdrivers. This board has no external protection diodes. DOes the TB6560 have internal protecting diodes?
If no what type of (very fast) diodes would you recommend for a maximal current of 3.5A?

best regards
Stefan

Comments

  • PJAllenPJAllen Banned Posts: 5,065
    edited 2012-12-15 06:13
    I figure it's most likely that touching at 'X' couples stray AC into the '244 (Hi-Z in).
    But what's the need to manipulate the wiring at 'X'? Is it OK otherwise?
    A ULN2803 would be a better choice, I think, if you're stuck on ICs. Its inputs are medium impedance.
    I'm stubborn - so I would just use simple transistors.
  • StefanL38StefanL38 Posts: 2,292
    edited 2012-12-15 07:52
    Hi PJ,

    thanks for answering. In the meantime I tested my interface with added 50k-Pulldown-resistors and now it seems to work reliably.
    Even when I touch "X" everything works fine. As I have 8 channels I wanted something with 8 channels in one package.

    The 74ACT244 was the one that I had handy. But the PIN-Out is terrible. I looked into the datasheet of the ULN2803
    The pin-Out is perfect: one side input other side output and GND / VCC at one end.

    Thank you for pointing me to this Chip
    best regards
    Stefan
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2012-12-15 08:40
    Pin 10 isn't a device power pin.
    Each output has a flyback diode anode connected to it and the cathodes are all ganged at Pin 10 ("COM").
    When the outputs aren't connected to inductive loads then you can leave pin 10 alone (unconnected.)
  • StefanL38StefanL38 Posts: 2,292
    edited 2012-12-15 08:56
    Hi PJ,

    so how can this device be used?

    Prop-IO-Pin
    ULN-INput--ULN-OutPut
    Parallelport ???

    Or with a LED would the schematic be:

    Prop-IO-Pin
    ULN-INput--ULN-OutPut
    LED----Resistor
    Vcc ???

    Maybe others can chime in: I wrote a second question in the first post:

    Does the TB6560 have internal freewheeling diodes?
    If not does he need them or can the TB6560 stand back-EMF?

    If I need diodes what superfast diodes would you recommend for a max current of 3.5A?

    best regards
    Stefan
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2012-12-15 11:18
    StefanL38 wrote: »
    so how can this device be used?
    Prop-IO-Pin
    ULN-INput--ULN-OutPut
    Parallelport ???
    Yes, since your PPI already has pull-ups. Note, though, the bubble on the "gate" - that makes it an inverter (LOW on IN gets HIGH on OUT).
    StefanL38 wrote: »
    Or with a LED would the schematic be:
    Prop-IO-Pin
    ULN-IN___ULN-Out
    LED----Resistor
    Vcc ???
    Yes. (When the IN is HIGH then the output is LOW.)
  • kwinnkwinn Posts: 8,697
    edited 2012-12-15 17:20
    If you only need a buffer to go from 3.3 to 5 volts take a look at the 74ACT541. Same function as the 241 with better pinout. All the inputs on one side and outputs on the other. This is also true of the other 5xx series chips.
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