I have just published my source code to generate four SSVEP stimuli on my github. Check them out if you are looking for a stable stimulation source.
https://github.com/taro10h/flicker_stimulator
Collecting ECG signal with TI ADS1299 daughter card and STM32F4 Discovery
Getting started with STM32F4 Discovery and Keil C 5 Tutorial
ECG signal from a simulator
Collecting EOG signal with ArmBrain [updated]
From Arduino to ARM Cortex M4 (STM32F407 Discovery)
SSVEP based BCI game with my hardware WEEG [Video]
My Open Source Flickering Stimulator For SSVEP BCI (MATLAB - Psychtoolbox)