Transistor/Mosfet suggestions

Using Arduino Motors, Mechanics, Power and CNC
#1

Hi All,
I have a need to control 8 automotive relays from a Mega 2560 board and I'm looking for suggestions on the proper component to use. I'm assuming I'll need a Darlington Transistor or a MosFet as I suspect the task to be beyond a standard transistor.

The relays I'll be controlling are these: http://www.mouser.com/Search/ProductDetail.aspx?R=301-1C-S-D1-12VDC

Basic specs are:

Coil Voltage: 12 VDC
Contact Form: SPDT (1 Form C)
Coil Resistance: 123 Ohms
Coil Current: 97.5 mA
Contact Rating: 35 A

The relays will be switching the high side in an automotive environment (nominal 12V DC, Neg Ground)

I'm also considering using opto-isolators between the Arduino and the transistors/mosfets if that makes a difference.

Any advice would be appreciated.

Thanks,
Keith

#2

100mA is no problem for most small switching transistors. You can use ULN2803 to switch all 8 I think
(check the total current spec though). The ULN2803 has freewheel diodes built in which is useful, just
connect COM to +12V.

#3