floating power supply

[labview1958]

I have connected the output f a schmitt trigger to 6025E daq board. I am trying to measure the frequency of a signal using the one counter method. It is not working. Someone suggested using a floating power supply. What is that? Can I used the 5V supply from the daq board to power my schmitt trigger? I read smewhere that the rise time for a signal must be below 50ns for labVIEW counter to measure the period. Is the rise time from the schmitt trigger less then 50ns?

[AnalogKid2DigitalMan]

Previous discussion here:

http://forums.ni.com/ni/board/message?board.id=170&message.id=181561

A floating power supply has no electrical reference to the ground of you circuit. It is "floating" above ground, no physical connection as a metaphor. A battery for example.

Yes, you can use the 5V from the DAQ card to power your circuit as shown in the other thread above. This will not be a floating source, but it will not matter for your application.

The LM319 used in your circuit is not a schmitt device, I think it's rise/fallresponce is 75-150nsec depending on the voltage that is powering it and the capacitance of the load. You could use a 74F14 inverter as the final drive stage into the DAQ card as an example.

Do you have access to an experienced electrical engineer at your place of work? I would strongly suggest seeking one out for a face to face meeting. Explaining and troubleshooting circuitry is quite hard to do remotely in a forum such as this.

[labview1958]

Since the rise time is more than 50ns, I suppose I cannot use L319. What shall I use?

[McKala[DE]]

Have you tried the 74F14 inverter that AnalogKid2DigitalMan suggested?

Regards,