Low frequency measurement from Parallel Port

[puccaku]

Hi there...

I need to calculate the "on" and "off" time and duty cycle in pulse form from a parallel port. By making the circuit in 5 or 0 V, I just simply put it in my parallel port. The problem comes when I need to measure a very very low frequency. In this case, I want to measure the duty cycle from my operated refrigerator. I need to know when the thermostat goes "on" and when it comes to "off". In my experience, the thermostat will be "on" in about 5-10 minutes and "off" in about 20-30 minutes. So, the pulse might be take for a long periode each.

I've tried with Timing and Transition Measurement wizard or even by using Pulse Measurement.vi which is included in Waveform Measurement category. It only works for 2 Hz and . If I try to set it with 1 Hz or below, it comes the message :

"Error -20308 occurred at Timing and Transition Measurements -> Untitled 1
:4"  (waveform index 0 of 1)

Possible reason(s):

Analysis:  The waveform did not cross the mid reference level enough times to perform this measurement. Check the signal length, reference levels, and ref level units."

Could someone help me please ?

Regards,
Ricki

[Henrik_Volkers]

How about polling the port every 100ms and do the calculation based on the PC clock?

You didn't mention your spec, however .2s error sound acceptable in this case.

[puccaku]

Dear Mr. Henki,

I've tried to make a 100ms polling, but it doesn't work. Then I saw Pulse and Transition Measurement.vi from the examples directory. I put the same value for the frequency and it also comes the same error message.

Or maybe you have your own program to measure a low frequency ? It doesn't have to be from parallel port. I assume it will be fit to any kind of measurement method. I still need your help, please ?

Ricki

[Henrik_Volkers]

here is a quick shot to give you an idea