how can I measure the time difference between spikes (interspike intervals)

[saraydin]

I have used NI USB-6008 (DAQ) to sample a continous signal, after sampling I compared the amplitude of the resulted signal with a value. If the amplitude is greater than a specific value (threshold) then it can pass. Now I want to measure the time difference between the resulted samples. The samples look like spikes. (May be if I trigger a timer, then I can measuer the time difference, but I have not seen such a timer). 

Thanks in advance,

Saraydin

[falkpl]

Depending on your signal you can use an edge seperation for digital signals or you can do continious analog acq and calculate the edges in software.  This all depends on the timing and what you mean by spikes?

[saraydin]

Thank you!

I mean the Spike (in nervous system), for better understanding check this: http://en.wikipedia.org/wiki/Spike_train

[falkpl]

OK, then I would think about using continious acquisition on 1 or more AI channels since these are not digital signals and processing the data in a second loop.  The nervous system is not all that fast looks like spikes are 50us long and probably have sufficient recovery time to discriminate between pulses.

[falkpl]

Oops just occured to me that you are using a 6009 which is not very fast, 48ks/sec, this will not get you very much time resolution and you could have issues seeing much of a 50 us sample.  Another approach is to use the counter but you would have to preprocess the spikes to generate a trigger for the counter.

Paul

[PaulG.]

Have you tried using the Peak Detector.vi?