Using USB 6501 to read magnetic sensor

[johnsold]

It depends on the base current requirements of the transistor.  It sounds as though you do not have much circuit design experience, so it would help if you specified the darlington array part number and the load current at the collector of the darlington.

Lynn

[jag213]

I am using a ULN2803A. I believe this is the correct datasheet https://www.sparkfun.com/datasheets/IC/uln2803a.pdf

It has also occurred to me that I may need to invert my logic out of the USB 6501 since the daq powers up in with the pins high and I don't want to trigger all my relays at once. That being said would I still need a resistor in series if I have my daq connected through a hex inverter

[johnsold]

The VI(on) on-state input voltage is specified as 2.4 to 3 V, maximum, depending on the load current, so what you are seeing is normal.

These devices are designed to work with TTL and CMOS 5 V logic circuits. You should be OK with the inverter without any additional resistance.  The device has a 2700 ohm resistor internally.

Lynn