I want to control a 6 solenoid valves(Operates at 24DCV and 0.5A) with the use of 6 relays connected to an Arduino's 6 pins via 6 BJT(NPN) Transistor.
The Arduino output pin is 5V and can source 40mA maximum.
I would like to use a relay to switch the valve on and off.
So, suggest me that which transistor is better to use here and value of resistor that I have to put between arduino and transistor. and DC voltage for relay to operate.