When using the BD135 solenoids, up to 1 A can be driven. The reader must experiment with resistor values if other transistors are used. Darlington transistors can be used if high-power solenoids are installed. You can replace the resistors with 10 k Ω units in this case.
Figure 1 - Using CMOS logic
When using with microcontrollers such as Arduino, the logic power supply voltage must be 5V, but the relay supply can be according its type, between 5 to 12 V.
