Signal Wire Length

[EricWilliams]

Originally Posted by EricVanWyk

I'd be very surprised if your digital signals suffered from resistive drop. Also, FIRST uses some very slow signals, so I again wouldn't panic.

For more information on the GPIO signal pins, you should look up the NI 9403's Operating Instructions and Specifications.

For information on the power supply capabilities of the DSC, look in section 3 (page 27) of the control system manual.

I'd be much more concerned with the amount of noise coupled in over those 14 foot runs.

From the Control System's manual:

• 5V/3A buck power supply for DSC circuitry with excess power available at the GPIO and I2C headers

Does this mean the DSC will source 3A to a nearly shorted connection, such as a depressed limit switch? What does "excess power" mean?

From the NI Documentation, Digital logic levels:

• Input
  • Voltage .................................–0.25 to 5.25 V
  • High, VIH..............................2.2 V min
  • Low, VIL ...............................0.8 V max
  • Hysteresis, VH......................0.2 V min
• Output
  • High, VOH.............................5.2 V max
    • Sourcing 100 μA ...........4.75 V min
    • Sourcing 2 mA...............4.4 V min
  • Low, VOL
    • Sinking 100 μA .............0.1 V max
    • Sinking 2 mA.................0.26 V max
• Input current (0 V ≤ Vin ≤ 4.5 V)...... ±250 μA max
• Module output current .....................64 mA max
• Input capacitance .............................. 30 pF

Does the "Input current" mean that the module itself limits the input current to ±250 μA, or that is the maximum input current allowed into the module?

Finally, would adding a bypass capacitor across the ground and signal pins help reduce noise?