Fig. 1

Stimulator design. a. A fully assembled stimulator. b. Rendering of the custom-printed circuit board which accommodates the microcontroller, the LED driver and up to 24 LED channels. c. Schematics illustrating the circuit that controls the LED output. The blanking input can be inverted by a switch before reaching the output enable pin on the LED driver (electronically switching off the LEDs) and sending the signal to the micro-controller. A second switch controls the blanking signal voltage as it needs to be adapted depending on the logic of the microcontroller used (3.3 V for ESP32, 5 V for Arduino). The microcontroller controls the LED driver through an SPI connection and sends a trigger signal output to an external DAQ-system. KiCAD schematic are available on the GitHub repository. d. Illustration of the raster scan method described. The “blanking signal” is synchronous with the scanning logic, enabling the LEDs during the scanning mirrors retrace (black) and shutting them off during the acquisition (red), therefore providing temporal separation between stimulation and detection (schematic in (d) inspired from [6]).