SN74LVC8T245
Can this device drive a signal line length of approximately 6 feet?
Thanks
Hey Peter,
Thanks for the details. The primary concern will be surrounding the edge of the signal when the device switches. Since it's not a high speed application, you have less to worry about, but a single switching event can still be problematic due to high frequency components and the parasitics on the line.
For example, if your transmission line is RG-58, a 50 ohm line with ~100pF per meter, then you'd expect to have about 180pF of parasitic capacitance and 450nH of parasitic inductance in a 6 foot (1.8m) length (assuming I remember these values correctly - you can calculate it yourself starting from Z_0 = sqrt(L/C) ). Here's a simulation of the expected output after this - negating other transmission line effects and only focusing on the lumped parasitics:
The different waveforms shown are for different strength drivers - {10, 25, 50, 100} ohms.
It's likely that the NI PXI digital I/O device doesn't care about the edge rate of your signal, but it might have issues with significant overshoot (like the strong driver example that's hitting 8.56 V). I would recommend using a series resistor on the output to slow the edge and prevent ringing/overshoot. 100 ohms should be plenty for a damping resistor.
