07-27-2006 06:34 AM
07-27-2006 08:09 AM
How accurate must the pulse be ?
If accuracy is not critical, use a DO (digital output) of the card and generate the delay by software (set DO, wait delay, reset DO).
Otherwise, you could use an external circuit (eg SN74LS390) to divide the frequency of the counter output.
07-27-2006 09:49 AM
In addition to JB's ideas, here's another one if your other counter isn't being used.
Use the other counter to generate your own custom clock. Let's suppose it's at 1000 Hz. Then setup the counter you really care about to use the 1000 Hz clock signal as its timebase. This will extend your duration capability by a factor of 100.
Your duration limit is based on the ratio of count register size to timebase frequency. Your board's counters max out at 2^24. Your max duration is approximately (2^24 / timebase freq). The lowest internal timebase is 100 kHz which is why you're limited to about 167 seconds. With your custom 1 kHz clock, you'll get 100x that much.
-Kevin P.
07-27-2006 10:43 AM
Thanks to both of you,
It helps me a lot.
The pulse does not need to be accurate. The most important think for me is to have a long pulse width (typically I would like the counter to stay in high state for 10mn). It is used to open a shutter. The shutter is opened when the TTL signal is high and closed when the TTL signal is low. I need the shutter to be opened for 10 minutes.
I will try your suggestions,
07-27-2006 10:46 AM
With what you describe, JB's software-timed digital suggestion sounds like a clear winner. By far it's the simplest to implement.
-Kevin P.