LabVIEW
200077 error lab view electrical stimulation
Hello Thierry,
To answer your question:
We are trying to stimulate a certain target area in the brain of a rat using an implanted electrode (deep brain stimulation).
This electrode is connected to a Stimulus Isolator, which is hooked up to the National Instruments card, connected to the computer.
We want to stimulate for 60min with a biphasic block stimulus at a high pulse frequency (60Hz) and a low frequency (130Hz) to evaluate the difference in effects. But the stimulus is calculated in such a way that their is a waiting period (interpuls interval) in between each pulse.
In the frontpanel we want to define how long the stimulation has to last (total time 60min), at what frequency we want to stimulate (pulse frequency 60 or 130Hz) and how long the biphasic block lasts (pulsewidth, 200microsec). The other data is calculated in our programme.
I'm not entirely sure wether the signal is TTL compatible as I'm not familiar with the term. However what is important is that their is no raisetime or fall time. The signal has to be given immediately and when the total time has passed the current has to be zero. No direct current can be given during or after the stimulation. Otherwise our data is comprimised.
I hope this has answered your question, if not let me know.
Many thanks for keeping an interest in our problem. We hope you can find a solution.
Kind regards,
Viki
Viki,
How is 60 Hz a higher frequency than 130 Hz? Are those the only pulse repetition frequencies you will use?
What resolution do you need on the pulse width? Is 200 us the minimum pulse width you will ever use? What is the maximum pulse width?
It appears from your print screen image that you are leaving the amplitude always set at the default 10 V. Is that correct?
It is physically impossible to generate a signal with zero rise time. The 6251 has a slew rate of 20 V/us so the central transition from +10 V to -10 V in your pulse will take about 1 us. For brain stimulation this is a negligible rise time but you should be careful in your use of terminology. When you try to publish your results, the reviewers may not be happy with claims of zero rise time and such language may raise doubts about your kowledge and understanding of the measurement instrumentation and process.
The AO buffer on the 6251 holds a maximum of 8191 samples. At the 50 kHz sampling rate of the square wave generator that covers <164 ms. The 1000 samples you generate occupy 20 ms. This will not give you the pulses you want. I canot save back to 7.0 but the screen shot below will give you some idea of how you can look at what is going on. Autoscaling (X) is turned off on both graphs. One shows the first 500 us and the other shows 20 ms of the signal you are generating.
Lynn
Viki,
I suggest generating just one pulse of the desired width using the Pulse Pattern.vi twice. Then create an array of zeros with the appropriate length to match the interpulse interval. Append the array of zeros to the array for one biphasic pulse. Write this to the AO buffer. Use the regeneration mode to repeat the cycle until the specified stop time occurs. The image below shows how to generate a 200 us biphasic pulse. Note that it gets the sampling frequency from the same cluster you used for the square wave. You could provide the frequency by other means.
Lynn
