How can I use my Arduino together with an external power supply?

Question

I am trying to design a simple square wave inverter (15V input from my power supply). For this purpose I will design a H-bridge with 4 MOSFETs controlled by the Arduino (5V or 3.3V output). The thing is, how can I make my power supply and Arduino work together? I only need the Arduino to control transistors (to make them let current pass).

Sorry for the bed design, as it is my first year in Electrical Engineering. This is the incomplete circuit design. The transistors in the scheme will be controlled by the Arduino. It will make blue ones OPEN first, then it will make red ones OPEN. So polarity will constantly change for the "Device." But I don't know how I can integrate the 5V Arduino here.

Answer 1

You connect the Arduino ground to the ground of your power supply and H-bridge driver. Make sure that the high currents have a direct ground path from the H-bridge back to the power supply and not through the Arduino's ground.

Figure 1. A simple driver circuit for H-bridge. Image source: Bristol Watch.

• Since the Arduino can only switch up to 5 V it cannot "reach high enough" to control Q1 and Q3. For this reason the 4.7k pull-up resistors are added and the 2N2222 transistors (or any small NPN) are added to turn on Q1 and Q3.
• Note that Q1 and Q3 are PMOS; Q2 and Q4 are NMOS. Your design shows four NMOS. You can do that but the switching circuit will be more complex.
• Connect Arduino ground to H-bridge ground.

Answer 2

Different machines/circuits can connect their SIGNALS together while having different power cables with different voltages running to them. What matters in this case is that the signal ports connecting to each other can handle each other.

More applicable for your H-bridge is below. Inside the MOSFET transistor is a barrier between the gate and the rest of the MOSFET. That barrier blocks the 15V from getting to the 3.3V (within reason). It allows a smaller signal applied between the gate and source terminals to control a larger signal across the drain and source terminals.

The base terminal of a BJT (another common type of transistor) is similar.

^{simulate this circuit – Schematic created using CircuitLab}