harsh Posted August 4, 2004 Report Share Posted August 4, 2004 i need a circuit to turn a relay on and off.the relay controls 12 volt fans.the control condition is heat, which comes from my refrigerator, and the fans vent the heat away from the cooling fins.so when frige comes on i would like to have the fans come on shortly thereafter.and when the frige goes off i would like to have the fans go off.i could even do it without a processor using an a/d converter, but i dont even want to use an a/d converter, seems like overkill.the circuit should be simple , maybe using an op-amp ,maybe.options: thermistor with changing resistance..but how do i turn a changing resistence into what i need ?driveing the relay isnt a problem assuming i have a signal to drive it with.so i have a changing resistance ,and i am working with 12 volts i think the relay is 12 volts alsoThank you.william Quote Link to comment Share on other sites More sharing options...
MP Posted August 5, 2004 Report Share Posted August 5, 2004 Something like this? (See attached)MPTemp_Controlled_Fan_w-Thermistor.pdf Quote Link to comment Share on other sites More sharing options...
harsh Posted August 5, 2004 Author Report Share Posted August 5, 2004 thats exactly what i was looking for ;Di cant read whats written under the circuit :(the mic-502 is an op amp? Quote Link to comment Share on other sites More sharing options...
harsh Posted August 5, 2004 Author Report Share Posted August 5, 2004 i found it.. a fan controller huh .. nice...thanks Quote Link to comment Share on other sites More sharing options...
MP Posted August 5, 2004 Report Share Posted August 5, 2004 Here is the data sheet for the MIC502 in case anyone needs it. Also has a nice clear diagram in the data sheet for application.MPmic502.pdf Quote Link to comment Share on other sites More sharing options...
harsh Posted August 7, 2004 Author Report Share Posted August 7, 2004 i decided to try a comaprator .. the LM339 quad comparator..and it worked *yay*.. and is working as we speek. Quote Link to comment Share on other sites More sharing options...
harsh Posted August 8, 2004 Author Report Share Posted August 8, 2004 here is the circuit i built Quote Link to comment Share on other sites More sharing options...
harsh Posted August 8, 2004 Author Report Share Posted August 8, 2004 all parts can be gotten at radio shack..PART LIST1) Thermistor1) LM339 Quad Comparitor1) IFR 510 Mosfet transistor N channel1) 10K varible resistor1) 10K resistor2)330K resistors1)2.2K resistor Quote Link to comment Share on other sites More sharing options...
ante Posted August 8, 2004 Report Share Posted August 8, 2004 harsh,A suggestion, if you add some positive feedback you get a Schmitt trigger effect and a better on/off switch.Ante ::) Quote Link to comment Share on other sites More sharing options...
ante Posted August 8, 2004 Report Share Posted August 8, 2004 harsh,This is what I am talking about: http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/schmitt.htmlAnte ::) Quote Link to comment Share on other sites More sharing options...
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