16 Choosing Real World Output Drivers

We are measuring for mechatronics, meaning we want to use the measured values in real time to change something in the real world. That means we need outputs that will have a physical effect!

Even a robust microcontroller like the UNO doesn’t provide much current directly from the board. A few milliamps are enough to light an LED, but to have any effect on the real world, the outputs need to be used only as signals to control or switch larger currents. For on/off switching:

• Relays provide mechanical switching, although the UNO output provides only enough current to switch very small relays.
• Transistors (MOSFET for larger loads) provide solid state switching with very low current requirements from the signal source.
• Solid State Relays (SSRs) provide switching of AC circuits while optically isolating the signal circuit for safety.

Inductive loads like coils and motors require more complexity to control speed and prevent overloads, as detailed in these videos. The slides are available as a PDF (video 8:38)

Electric motors can provide rotational motion, or drive linear actuators and servos to move mechanical components of your design. (video 13:37)

Low side switches for DC power using NPN,  Darlington, and MOSFET Transistors to handle different levels of current. In this video they are just turning LEDs on and off, but they can handle much more under control from the Arduino. (video 1:55)

More about transistors from MAKE Magazine, covering both the ideas of amplification and switching. (video 8:56)