Probably the most important function of an electrical stimulator is ensuring that the target current level is correctly maintained.
This is an explanation of how foc.us control the current output in the foc.us v2.
There is a hardware current regulator which is controlled by the MCU. The MCU does not participate in current regulation, it just sets the target current value to the current regulator input. The hardware current regulator is very fast. It can change the output current from the minimum 0mA to the maximum 2mA in 300µ seconds at full impedance load. At lower resistance levels it can do it even faster.
There are three safety steps employed in the current regulation
- the current of the high voltage source is hardware limited to 2.1mA, which is fed to
- the hardware current regulator,.which as described above can quickly change the output current to the targeted value and then
- the final step is an independent hardware current limiter, configured to 2.1mA between the hardware current regulator and the electrodes
In summary, the input to the hardware current regulator cannot exceed 2.1mA, which is then shaped into the signal e.g. tdcs, trns, tpcs, tacs at the desired current level – which is limited to 2mA, and then passed through a final limiter before the electrodes. This provides super fast, super safe signal generation.
As part of the assembly process we test and verify that all three of these circuits are functioning correctly. We perform this test on every single device. 100% testing.