I'm using the Teensy 3.5 with a very popular project called Speeduino. Works very well. I wanted to implement the sd card slot for data logging the real time variables while the engine is running. I've got the sd card slot working and writing. But when it writes to the sd card all the other functions that are running, tach input, coil outputs, injectors and so on, flicker as if they are being interrupted. I'm not the best programmer in the world. That's why I chose the Arduino platform for this. But something is just not working right. I can post the code if needed. But there is a lot of it. LOL.