configure BioExplorer for the U-wiz
This is an introductory description. The full description of Wiz devices can be found under the Manuals tab.
The U-wiz is a two channel ExG bio-signal acquisition device, where ExG refers to EEG, ECG, EMG and SCP Modalities. It is principally a USB-direct connect device, but can also connect wirelessly. It targets tablet solutions but can work equally well with PCs. The U-wiz supports continuous electrode impedance measurement and electrode offset voltage measurement. ExG signals can be AC or DC coupled, and the two electrode references can be electronically linked. The U-wiz does not have any buttons – functions on the U-wiz are controlled by the Application, whether that application be BioExplorer, BioEra, or EEGer. Setup of the X-wiz occurs under direct-USB connection and not in wireless connection. Once the Wiz is configured as required under direct-USB connection, the Wiz will remember the settings and carry that into wireless operation.
“Mode” refers to the characteristics of the channels used to transport the bio-signals from the Wiz to the Application. Mode defines the sampling rate and the number of channels. “Modality”, on the other hand, refers to the different types of bio- signals supported, such as EEG, EMG, and ECG. Different modalities place different demands on the channel supporting them, thus for example, SCP can be supported on a low sampling rate channel and EMG demands a high sampling rate channel. The Wiz provides different Modes to optimally support different Modalities on up to four slots available for sending bio-signals to the Application.
Since the Wiz remembers certain parameters including Mode, in the most common usage scenario of single channel & single modality, operation reduces to
- connect the sensors,
- turn on the Wiz, and
- hit the play button on the Application.
The Modes available are listed below. The Mode light on the Wiz will blink once for Mode 1, etc.
<Mode 0> program mode – used to upload new firmware or interrogate firmware version number
<Mode 1> 2ch x 32sps – (EEG protocol processing – future)
<Mode 2> 2ch x 128sps – Hi resolution EEG
<Mode 3> 2ch x 512sps – EMG, ECG, Othmer and SCP – higher bandwidth, lower sensitivity.
<Mode 4a> 4 slots x 256sps – ch 3 & 4 used for electrode impedance of ch 1 & 2
<Mode 4b> 4 slots x 256sps – ch 3 & 4 used for electrode offset of ch 1 & 2 – invoked by command from the Application
In each Mode, the content on the two/four slots being sent to the Application depends on which sensors are active (ie plugged into the Wiz). In general, the design controlling the Application trains a particular Modality and therefore expects a particular Mode. The Mode expected should constitute part of the name of the design. The user should then set the Wiz to the Mode expected by the design. The table below is provided for reference.
|configuration||Slot 1||Slot 2||Slot 3||Slot 4||Comment
|EEG1||EEG2||EIM1||EIM2||continuous electrode impedance measurement
|EEG1||EEG2||Offset 1||Offset 2||continuous electrode offset measurement
The lights on the Wiz can be used to confirm that commands sent from the Application have been received:
|On steady||sending to Application via USB
|On blink||sending wirelessly
|Off blink||not transmitting to Application (ie Program Mode)
|4 blinks||acknowledging command received for Application
|No of blinks||wireless channel number
|On||no EEG lead off, and/or nIR full signal strength, and/or pIR valid reading
|Off||EEG pair off, or nIR not full strength, or pIR reading out of range
|Fast Blink||EEG single electrode off
|No of blinks||Mode 0/1/2/3/4 = Program/32sps(2ch)/128sps(2ch)/512sps(2ch)/256sps(4ch)
|On blue||EEG baseline frozen (DC coupled)
|Off blue||DC removal - EEG low frequency response ~0.2Hz
|On green||EEG References linked - only one Reference electrode required
|Off green||EEG References independent - two References required for 2 eeg channel operation
The Wiz Window in BioExplorer has the following functions for commanding the Wiz:
- Power – turn Wiz on & off
- EEG Link References – electronically connect the two eeg reference electrodes
- EEG Freeze Offset – instantly directly couple the ExG signal, DC offset removal is inhibited
- HEG Calibrate – not applicable, ignored
- Program – Mode 0: set this mode to update firmware or interrogate version number
- HEG – Mode 1: not applicable
- EEG – Mode 2: set this mode for EEG and minimum load on the PC processor
- ExG – Mode 3: set this mode for ECG. EMG, SCP and Othmer protocols, hi bandwidth and reduced sensitivity, Also set “Freeze” for SCP, Othmer & possibly ECG
- EEG+Impedance – Mode 4a: 2ch EEG and continuous electrode impedance measurement in ch 3 & 4
- EEG+Offset – Mode 4b: 2ch EEG and continuous electrode voltage offset measurement in ch 3 & 4
- 4Ch – Mode 4: not applicable, ignored
- Helper functions used occasionally
- Off – revert back to normal mode
- Electrode Impedance Check – interrupt the eeg signals to test for electrode impedance
- Electrode Offset Check – interrupt the eeg to test for electrode offset voltage
- Electrode-sense Off – turn of the current used to sense electrodes falling off to improve accuracy of DC coupling
- Test Tone – inject a test sequence of 4,8,16 & 32Hz at 1 second intervals to check Wiz is working OK
- Buzzer (not applicable)
- USB Only – turn off wireless
- 1…8 – turn on simultaneous USB and wireless, the latter allows monitoring of the eeg by a monitoring station
Checking the validity of bio-signals
There are a few things in the Wiz to enable you to check the soundness of the ExG biosignals (applicable to EEG, ECG, EMG and SCP).
First item is the “Test Tone” Helper function. This is available in the Wiz window in BioExplorer under Helper functions: Test Tone.
If ExG is active, the Test Helper function injects a tone right at the input of the Wiz, so in general, if the Test function is working, then the Wiz is working. If the Test signal is fine, but the EEG is flat-lined, then the first thing to check is that “Freeze” blue light is off. Freeze is switched on for working with SCP (& ERPs), Othmer low frequency protocols, and possibly ECG. Activating the Freeze function puts the Wiz into its DC-coupled mode. This means that the offset removal that is normally in place, acting to return the EEG signal to an average of 0 microVolt is deactivated. If Freeze is switched-on whilst the EEG is out of range, not yet having fully restored itself to an average of 0 microVolt, then it will stay out of range indefinitely. That is, the EEG will be flat-lined. For this reason the Freeze state is not remembered by the Wiz – each time the Wiz is started, it starts with Freeze off.
Also, if using one-channel EEG designs, you must use Channel 1 (aks 1+/1-, aka Left). If you use Channel 2 (or 3 or 4) without using Channel 1, then the feature of actively suppressing 50/60Hz interference is lost.
If these conditions are satisfied, then one should look to problems with the electrodes themselves.
In relation to electrode performance there are several layers of defense.
- First, the Red/Green information in the Status Bar of BioExplorer, give “electrode off” indications. This will actually identify which electrode has fallen off using the following code
- steady red light – both electrodes are off (or that channel is not in use)
- flashing red light – one of the pair of electrodes is dislodged
Linking reference electrodes can then distinguish which of the pair of electrodes is dislodged
- if the flashing red light persists when electrodes are linked, then it is the active electrode that has dislodged
- if the flashing red light goes steady green, then it is the reference electrode that has dislodged.
- Second, there are two Helper functions related to checking electrodes:
- “Impedance Check” and
- “Offset Check”.
Electrode impedance is a measure of the goodness of the contact of the electrode with the skin. Poor contact will result in a noisy EEG and quite possibly a large increase in 50/60Hz power line interference which too can lead to flat-lining. EIM is a measure of the impedance of an electrode pair, not a single electrode. So values under 20kOhm can be considered good and up to 50kOhm is quite serviceable. Offset Check is a measure of the voltage generated by the metal electrode together with an electrolyte (the paste) onto the skin. All metals will generate this voltage with Ag/AgCl electrodes having the lowest voltage. EEG systems are designed to tolerate this relatively large voltage, however gold-plated electrodes, when the gold plating wears or is otherwise compromised, exposing a different base metal, produces a particularly severe offset voltage that can cause the EEG to intermittently flat-line. Gold electrodes are not recommended. The Wiz can tolerate offset voltages +-250mV and so should not be an issue if gold electrodes are not used.
Mode 4a and 4b allow EIM and Offset respectively, to be monitored continuously. However if not in either of these Modes, for instance if using Mode 3 for 2ch EMG, then EIM and Offset measurement is invoked by selecting the Helper function Check Impedance and Check Offset. Once the measure is obtained, then Helper functions are set to Off, and the normal ExG operation is restored.