To determine laser diode switching time using labview

[M405]

Hello Folks,

I am using a laser diode and a photodiode for one of my biomedical application controlling using an NI DAQ 6002 card to continuously pulsate the laser diode, modulating it by ON/OFF for measuring the intensity across the photodiode through LabVIEW. Now, I have used a delay in the logic, and suppose if I change it from 500 ms to 200 ms I can see the change in laser On/Off. 

But, I need an exact value of this switching value (time). Please suggest me how do I can determine the switching time (how fast my laser switches between ON/OFF). Do I need to connect to the oscilloscope (output of detector)?

Your help will be highly appreciated. Please help me.

Regards,

[wiebe@CARYA]

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@M405 wrote:

Do I need to connect to the oscilloscope (output of detector)?

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Yes, if you have one that would be convenient.

Or something similar, like an AI DAQ device, maybe even a NI DAQ 6002?

I guess some frequency counters would do this too (calculate frequency and duty cycle).

It matters a lot how accurate you want this to be. A 6002 has limited capabilities (it's sampling rate, and it's clock accuracy).

[Henrik_Volkers]

the 6002 is much much slower than the laser diode..

well, it also depends on the driving circuit ;9

to measure the laser diode rise and fall times one usually use detectors at least 10 to 30 times faster than the time you want to measure.

Any scope that is digital in in any way will be faster than the 6002 (but usually with 8 bit resolution).

so it would be helpfull if you tell us the timing constrains you try to meet.

the 6002 counter has a resolution of 12.5 ns .. one bit ..

[wiebe@CARYA]

I agree, if OP wants to measure rise and fall time of the laser (driver), compared to the DO signal a scope is needed.

But "I need an exact value of this switching value (time). "

Could also mean OP wants to measure the latency of the digital system, e.g. the time between setting the DO in SW and the DO HW actually switching on\off.

A scope won't measure that, as it has no way to measure the switch in the software. It will be difficult in software too, as you still need to correlate the SW event to the incoming data.

In any case a 6002 is probably on the light side to do any serious measurement.