problem with sending different trigger to BrainVision Recorder with V-Amp, serial port

Lee

Dear community

Hi, I'm Lee, and it's my first time asking a question. Please understand If I'm not good at English.

I'm making simple oddball task for my ERP Experiment.

So I want to send different trigger at different stimuli.

but, BrainVision Recorder was received same trigger. just "S11".

at first, before start the experiment, I wrote the code like below at inline script(run).

import serial
import time

try:
	exp.port= serial.Serial('COM3')
	print 'serial port read', exp.port.name, exp.port.baudrate, exp.port.bytesize, exp.port.parity
except: 
	print 'serial port not read'

and the printed result of first inline script is here.

serial port read COM3 9600 8 N

and after each stimuli, I wrote the code like below.

value = var.triggervalue

t = time.time()
count = 0

try:	
	while (time.time()-t) < 0.005 : #500Hz: >4ms / 250Hz: >8ms
		exp.port.write(str(value)) # or whatever is appropriate
		count += 1
	print('trigger has been sent')
	print('value:',value,'    time:',time.time()-t,'    count:',count)
except:
	print 'trigger not sent'

self.sleep(200)

and the printed result is here. (value 1: prominent / value 2: odd)

trigger has been sent
('value:', 1, '  time:', 0.005000114440917969, '  count:', 58)

trigger has been sent
('value:', 1, '  time:', 0.00599980354309082, '  count:', 32)

trigger has been sent
('value:', 2, '  time:', 0.006000041961669922, '  count:', 36)

trigger has been sent
('value:', 1, '  time:', 0.006000041961669922, '  count:', 34)

trigger has been sent
('value:', 1, '  time:', 0.006000041961669922, '  count:', 67)

last, I end the experiment with this code

exp.port.close()

I expected this inline scripts would sent right trigger, but BrainVision Recorder received only "S11".

Why Recorder read the trigger only "S11", not "S1" nor "S2"? Where is "S11" from?

I read other forums(https://forumcogsci.nl/index.php?p=/discussion/491/solved-sending-different-triggers-via-serial-port etc), but I can't understand why and where I make mistake.

Could you explain what is wrong?

and I have one more question.

I send the trigger with "for" phrase, so I send lots of trigger at one time to handle nyquist  problem.

How can I send the only one and long trigger?

If you could correct my mistake, I would be much appreciated.

Thanks a lot.

eduard

Hi Lee,

I don't know whether this makes sense (I've never worked with Serial ports), but maybe you have unset a trigger before sending a new trigger. So in between exp.port.write(str(1)) amd exp.port.write(str(2)), send exp.port.write(str(0)).

I send the trigger with "for" phrase, so I send lots of trigger at one time to handle nyquist problem. How can I send the only one and long trigger?

One way is to send a counter, for example this:

counter = 0 
for i in range(100):
    if counter == 30:
        print(i)
    counter += 1

Eduard

Lee

Thanks for your reply, Eduard.

Actually, I found what I wrong just before.

I want to handle nyquist problem, so I send triggers with "while" phrase, (sorry, I have mistake. I wrote wrong word.)

but, It send wrong trigger.

with while phrase, I intended to send trigger [1,1,1,1,1,1,1...] -> [S1,S1,S1,S1,S1....]

but, serial port sent trigger [111111....] -> the max signal -> [S11]

photo at below is the result of serial port communication(that I sent to BrainVision Recorder).

Do you know How can I send only one and long trigger?

To solve Nyquist problem, when sampling rate is 500Hz,

One Trigger must longer than 4ms.

How can I make long trigger?

thanks alot.

Lee

eduard

Hi Lee,

If your experiment allows for it, you can sleep for a little while (e.g. 10 ms ) on every iteration.

for x in range(100):
    clock.sleep(10)
    print(clock.time())

Does that do the trick?

Eduard