Digital Input Trigger from Voltage Source

[mcbeead]

NI hardware used: PXI-6221 with the SCB-68. Other hardware: 24VDC 10amp supply, switches, and soleniods. The soleniods are turned on/off with a switches(22 in all.

What I am am trying to accomplish: use the digital inputs (all available) to detect when the soleniods are on and off. My first thought was to use a resistor to drop the voltage from 24VDC to 3.5 to 5 to trigger the input on a digital channel. After reading through the manuals I have decided it is more complicated than that. I will need to limit the current and I do not want to damage the DAQ card. If anyone has done this before or has seen this discussed in the forum please reply.

[fromm8]

Like you said, you need to be careful with the power limits, current and voltage

[mcbeead]

I will be using a voltage divider circuit. I found a suggestion to start with a 10K Ohm resistance across the Digital input. Use the volts in and the volts needed to calulate the line resistor. In my case it is 43K. This is working on the bench but I have not tried it on the DI yet.

[apok]

you could use voltage comparators, optocouplers, uln's....