Audio signal as Trigger

edmundlalor · Post by **edmundlalor** » Wed Jul 08, 2009 1:53 pm

Hi,

We wanted to measure the onset of a sound directly from the audio jack of our presentation PC to avoid any problems between the delays between triggers and sound onset. We connected the cable from the audio jack to pins 7 and 37 of the trigger input to the USB receiver, however we don't see anything coming in on the trigger channel in Actiview when the sound starts playing. Perhaps the audio signal is too weak, i.e. < 5 V? Does pin 36 have to be held high at 5V?

Thanks for any help.
Ed

Post by **Coen** » Wed Jul 08, 2009 2:30 pm

The inputs are TTL level, so you will need at least approx. 3 V (6V peak-to-peak for an audio signal).

Pin 36 is a 5V digital suplly output

Best regards, Coen (BioSemi)

edmundlalor · Post by **edmundlalor** » Wed Jul 08, 2009 4:54 pm

Thank for that,

We were also thinking of using one of the external channels to record the sound directly form the audio jack. We were wondering what is the maximum voltage that can be fed into the AD box without saturation? Also if this saturation voltage is exceeded will the ADC be damaged?

Thanks again,
Ed

Post by **Coen** » Wed Jul 08, 2009 5:09 pm

Only active electrodes can be connected to the EX inputs.

Do not connect an audio signal from a mains powered device to the AD-box. This will short the isolation barrier provided by the optical fiber, and will put the subject in a potentially dangerous situation (see manual).

For acquisition of analog signals from mains powered devices, you will need the Analog Input Box (http://www.biosemi.com/aib.htm).

An alternative in your case would be to use the microphone as offered in our accessories section (http://www.biosemi.com/accessoires.htm)

Best regards, Coen (BioSemi)