Hi

Yes I think there is delay. I tried before to measure EMG using arduino and send it via serial interace and bluetooth interface. The results in both senarios were not exactly the same. but differences are very very small.  

For sure both WI-FI and Blutooth devices have delay in data transmission. The main problem, when you use this device for reaction time task, is to measure this delay and check also if is constant or not. In my experience WIFI delay is very stable and approximately it's near to 14/15 ms, not the same for the bluetooh that shows more variability (jittter)

If you need to send marker to EMG is better to send it from the same channel used to send EMG. In this case both marker and raw signal are delayed in the same way.

Well, there is delay in any transmission, even in optical fibres. Question is how much. Transmission delay  should be specificied in the data sheets.

But I like to point your attention to another crucial item: Any port to peripherals (like Bluetooth) is served by a driver of the operating system, and when the driver is served by the CPU depends on the actual program task load situation. E.g., when you have enabled an online virus scan, the related disk activity can block the service of the Bluetooth driver. Same is true for stimulus generation on the screen; again, delays are possible. The PC together with WINDOWS is no realtime machine!

Werner

Thank you for your answer Werner.

Of course, we always disconnect our lab computers from the internet (software and hardware).

I think at the end we are going to buy the old cables :)

dear HI

your question is right. dear i have mentioned this link please visit this because it will help you ..

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1455479/figure/F1/

thanks 

Faisal,what should we learn from the figures (addressed by your link) with respect to the question of delays due to wireless transmission?

Werner