Someone will, no doubt correct me, if I'm wrong, as I'm not completely sure on this one. An SCR is like a locking relay: Once you turn it on, it's on. As far as I know, the only way to turn off an SCR once it's triggered is to lower the current through it to below the SCR's holding current, whether through another active device or through it being used in an AC system. (inherent current change 120 times a second due to reversing voltage) Your friend was probably thinking of an AC system, where this idea would work, but I don't think that for what you want it's practical. I'd suggest a power MOSFET or even a small relay. There are small enough relays that they can be used to activate larger relays from a logic device (like an MCU): They're what are used for the ouputs in PLC's since they provide better electrical isolation than a semiconductor device, and what you're implementing here is pretty close to a crude PLC. IMPORTANT: if you use a relay anywhere near a logic device of any kind, wire a diode backwards across the coil of the relay. If you don't do this, you will destroy the logic device from time to time due to voltage surges caused by the coil turning off. --Brendan ----- Original Message ----- From: "Erik Jacobs" To: Sent: Monday, June 17, 2002 10:18 AM 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? > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics > > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics