Details of what is a TTL compatible signal.

[Gene Z.]

I have a square wave signal produced by a differential hall effect sensor.  With a 75 ohm resistor it is from 0.525 V to 1.050 V.  I can increase the delta V with a greater resistance, say 200 will produce 1.4 V to 2.8 V square wave signal.  Is this still not a TTL signal, because the V(IL) is not less than 0.8 V?  Will any device read this signal?

[Hani R]

Hi Gene,

You are correct in stating that a square wave from 1.4V to 2.8V is not TTL compliant.  I just have a couple of questions about your application.  What is the frequency of your signal?  What DAQ card are you using and are you using LabVIEW or a different programming environment?

There is a way to count the pulses on a non-TTL signal by using an analog input channel and a counter.  There is a Developer Zone example, DAQmx: Counting Non-TTL Pulses with Multifunction Board and LabVIEW and a KnowledgeBase article KB 2I5DAAXA: Is It Possible to Count Non-TTL Pulses with an E Series Data Acquisition Board? which describe the setup in LabVIEW.  Essentially, when the non-TTL signal crosses a specified threshold, it generates a trigger which is then routed to the counter.

[Gene Z.]

I am using a PCI 6220 card and it does work with a non TTL signal.  Thanks.