Generally when you think automotive, expect the devices
(relay) to run at ~12V, and for that you'll need a driver.
(Even with a non-automotive relay, you'll need a driver.)

Driver can be a simple transistor (2N2222 or similar) with
a resistor to the base and a rectifier diode across the
relay coil.  I'm not too good with ASCII graphics, but you
can search google for "transistor relay driver" and you
should come up with many options.

Cheers,
-Neil.




-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Erik Jacobs
Sent: Monday, June 17, 2002 12:19 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: [EE]: interfacing a a relay (automotive world)


I apologize in advance for posting this message... my flame shield is on :)

I'm embarking on a automotive project using a PIC that will control some
electric fans.  The "parts" involved with this portion of the project are
the PIC, somet interface, and an automotive relay.  I should probably find
some specs on an automotive relay but I'd assume that it only needs a few
volts to engage and a very small constant voltage to keep it on.  I highly
doubt that a little output port on a PIC micro is going to be able to drive
a relay, so I'm wondering what kind of intermediary device I would need.  I
was thinking something along the lines of a power transistor, but someone
suggested to me using an SCR(?).  What are your thoughts/ideas/experiences?

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