This circuit is an isolated shield for microcontrollers such as the Arduino, MSP430, PIC and others. In the simulation the load is an incandescent lamp but it can be replaced with motors and solenoids. According the transistor is the load current. The transistor must be mounted on a heatsink. In the simulation a 5 Hz sinal is applied to the shield to make the lamp blink. Circuit is given in figure 1.