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The data on the trigger lines is latched 1.4 microseconds before the falling edge of the clock (sample rate) signal (pin 32). The timing relative to the falling edge in the clock signal is the same for all sample rates (speedmodes).

Best regards, Coen (BioSemi)

The PCMCIA version of the National Instruments digital I/O card can indeed only handle approx 32 channels. For the ActiveOne, no alternative is available. Our USB2 interface (http://www.biosemi.com/receiver.htm) works great with laptops for all (256) channels, but it is only available for ActiveTwo ...

You can order some extra electrode holders from us, and mount them at the preferred locations in the cap yourself (see http://www.biosemi.com/faq/make_headcap.htm). Use some pin type active electrodes with touchproof connector for these extra channels.

Best regards, Coen (BioSemi)

It is not posible to calculate the electrode impedance from the offset values. Why would you need to know the electrode impedances on an active electrode system ?

Best regards, Coen (BioSemi)

Question 1): Scenarios like the above will always also lead to increased current via the DRL lead, since the DRL essentially is a (current limited) low impedance connection to the amplifier Common. In case of a situation with multiple defects the current sinks and sources will not cancel each other ...

As soon as the DRL circuit runs into its 40 uA current limit, the power supply to all active electrodes is shut down. This prevents excessive current flow in case of multiple active electrode defects. In other words: the DRL current limit prevents too large currents between a defect active electrode...

Each chart always displays a fixed number of samples: 1024 for the low resolution versions, and 2048 for the high resolution versions of ActiView. So, the amount of downsampling depends on the selected sample rate (combination of speedmode and decimation), and the selected screen length in seconds. ...

Because of the battery power supply and fiber optic data transfer, the ActiveTwo front-end is fully floating (galvanically isolated from the environment). Therefore, the ActiveTwo does not "know" whether other measurement devices are connected to the subject. So, there won't be any problem when you ...

1) and 2) Already answered above: the impedance between the GSR electrodes is measured and recorded in ActiView. 3) The absolute impedance is measured and saved to file, only the changes are displayed in ActiView. 4) Negative impedances cannot be measured. 5) The BDF file contains data converted to ...

Please refer to the ActiView diagram (source code). In subvi "Convert_4-7Switch.vi", the peak-to-peak value of the 512 Hz signal measured between the GSR electrodes is determined. The peak-peak values are resampled to the original 2048 Hz, and added to the data array as the GSR channel. In subvi "Se...

You can delete all charts and associated controls and subvi's without any problem. I would just recommend to keep using the buffer clock (lower right corner), as an indication of the buffer read process. Do not change the basic structure of function calls to the USB driver library. Also, I recommend...

Your AD-box is functioning as intended, this issue is described in the manual, and also discussed on viewtopic.php?t=32.

Best regards, Coen (BioSemi)

I recommend to use our ActiView as an example, use the latest version for the PCI card, 4.09, which can be downloaded complete with source codes from http://www.biosemi.com/download/LatestActiView/ActiView409/ActiView%20V4.09.zip . The source code of the subvi's that read the PCI card can be accesse...

Your explanation is now clear and correct, but your conclusion is still (partly) wrong. In the unreferenced (raw) signals you cannot see activity in the electrodes close to CMS. So, in your situation 2 (Oz close to CMS), it is not true that "one can see negative peaks at Oz before (..) referencing"....

The above view of the operation of the CMS/DRL loop is fully incorrect. The CMS/DRL circuit cannot change the current distribution caused by physiological voltage sources. No extra current is sourced/sinked via the DRL (there is nowhere any current could flow, all other electrodes are connected to h...

A downsampling tool is now available from http://www.biosemi.com/download.htm --> http://www.biosemi.com/download/BDF-to-decimatedBDF.zip

Development of the tool was not much work, mainly a matter of cutting and pasting some existing pieces of LabVIEW diagram.

Best regards, Coen (BioSemi)

A constant current via the GSR elctrodes causes a voltage across the electrodes proportional to the impedance between the GSR electrodes. This voltage is measured and presented in the unit Ohm

Best regards, Coen (BioSemi)

The EX1-8 ("touchproof") electrodes are connected to channels 232 to 239 (234th to 241th incoming 32-bit word). The last 16 channels (240-256) are reserved for the additional sensors. The above is valid for speedmodes 0 and 4. On speedmodes 1-3, the EX and sensor channels are not sampled. On speedmo...

ActiView displays as: positive = upwards.

The above interpretation of the Y-scale setting is correct. The selected Y-scale number is the distance between two adjacent signal traces (Y-scale tics).

Best regards, Coen (BioSemi)

Let me explain by starting with the most simple setup, and then making thing more complicated step-by step until we end up with the actual ActiveTwo configuration. The initial goal is to measure the potential difference (voltage) between two electrodes. 1) The most simple setup is to use one Ground ...

From Ohm to uMho (uSiemens): take reciprocal (1/x), and multiply with one million (1,000,000). Beware: the reciprocal of a CHANGE in resistance (Ohm) is NOT a valid CHANGE in conductance (Mho), because: (1/x1 - 1/x2) is not equal to 1/(x1-x2). So, take the reciprocals of the individual data points b...

The current flow via the DRL is constantly monitored by the safety circuitry inside the AD-box. The current flow is limited to 50 uA (IEC 601 safety limit). If the current runs into the limit, the CMS/DRL circuit cannot keep the Common Mode value within its normal working range, and the blue LED tur...

The GSR data is measured in Ohm, and this is also the "physical dimension" listed in the BDF header for the GSR channel (13th header field, see http://www.biosemi.com/faq/file_format.htm). The problem with Brainvision Analyzer is that the header information concerning physical dimension is ignored. ...

Thanks for the feedback.

Just one further comment: the firmware upgrade is only necessary for USB receivers delivered before May 2004. The later batches are already programmed with the current V1.1 version.

Best regards, Coen (BioSemi)

Use the 2D array coming from the subvi Downsample-24sinc.vi. This array contains the raw data, and is used for the subvi's that calculate the chart traces, and for the data set saved to file. Do not use the arrays going directly to the charts: the data at that point is referenced, filtered, baseline...

It is mentioned both on our website and in the manual that the USB drivers only work under Windows XP. The "no incoming data" problems are caused by a combination of chipset and operating system. There do indeed seem to be a few chipsets that work OK under W2000. However, it is unlikely that we can ...

The BioSemi USB drivers are designed only for Windows XP. We have not tested the drivers with Windows 2000, we can not advise in case of trouble.

Best regards, Coen (BioSemi)

This is a known problem with some USB cards. A firmware update and Windows patch are available on the Biosemi websit, please see viewtopic.php?t=23

Best regards, Coen (BioSemi)

The considerations concerning the measurement situation and general setup of the acquisition system are still very valid. However, because of the new opportunities offered by modern electronic components. the hardware implementation examples in the papers can not be regarded as state-of-the-art anym...

Full specifications of the BDF format are found on http://www.biosemi.com/faq/file_format.htm The LabVIEW code to write BDF files is freeware, you can download the latest ActiView complete with source codes from http://www.biosemi.com/download_actiview.htm. However, you have to have the LabVIEW prog...