threephase effects - diglet48/restim GitHub Wiki
When operating a device with a single channel, current flows directly between two electrodes. The intensity ratio between two electrode can only be controlled by making electrode smaller or larger.
When adding a third electrode, we create what is called a three-phase configuration. Careful signal generation allows for adjusting the intensity ratio between electrode without adjusting their size.
The definition of three-phase has led to much confusion. While all devices with two channels can be wired in three-phase, and thus could be considered three-phase capable. Some devices can only generate a small subset of available sensations. Those can, in my opinion, not be called true three-phase.
Below is a series of signals that demonstrate fading in/out a single electrode. The numbers are understood as the amplitude of the waveform.
Below are some signals that demonstrate focussing a particular electrode.
Finally, some signals that demonstrate smooth rotation. A reasonable approximation can be made interpolating rows 1 to 6, but it doesn't feel quite the same as 'analogue' rotation.
The coyote is only capable of generating row 1 and 2. For best effect connect the neutral to the least sensitive electrode.
The NeoDK (4-triac version) in three-phase mode is capable of generating rows up to 5, assuming the skin resistance of all electrodes matches.
Stereostim and FOC devices are capable of generating all 9 rows. Even if the skin resistance and nerve sensitivity differs. Practical use requires that the difference in electrode sensitivity is less than a factor of 2.
Four-phase
The concept can be extended to four electrodes, demonstrated by NeoStim family and FOC-Stim V4. This greatly expands the range of sensations. The FOC-Stim V4 is capable of generating all possible current paths between 4 electrodes.