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<TITLE>Driving a bunch of solenoids (cheaply)</TITLE>
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<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT COLOR="#1F497D" FACE="Calibri">I want to drive 16 solenoids</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT COLOR="#1F497D" FACE="Calibri"> (</FONT></SPAN><SPAN LANG="en-us"></SPAN><A HREF="http://www.sciplus.com/p/12-VDC-SOLENOID-VALVE_49518"><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><U><FONT COLOR="#0000FF" FACE="Calibri">http://www.sciplus.com/p/12-VDC-SOLENOID-VALVE_49518</FONT></U></SPAN><SPAN LANG="en-us"></SPAN></A><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT COLOR="#1F497D" FACE="Calibri">)</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT COLOR="#1F497D" FACE="Calibri">. They are 12V, 100mA devices. At most 8 will be on at any time. Assume 100% on time for any one device.</FONT></SPAN></P>
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<P DIR=LTR><SPAN LANG="en-us"><FONT COLOR="#1F497D" FACE="Calibri">I have been using this N mosfet</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT COLOR="#1F497D" FACE="Calibri"> for driving motors for my cat feeder and drip irrigation:</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en"> <FONT COLOR="#333333" FACE="Helvetica">FQP30N06L</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT COLOR="#1F497D" FACE="Calibri">It works for driving the solenoids.</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT COLOR="#1F497D" FACE="Calibri"> However, being a cheapskate, I am wondering if there is something less expensive</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT COLOR="#1F497D" FACE="Calibri"> (</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT COLOR="#1F497D" FACE="Calibri">FQP30N06L</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT COLOR="#1F497D" FACE="Calibri"> is $0.95 at Sparkfun, more at Digikey)</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT COLOR="#1F497D" FACE="Calibri">?</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT COLOR="#1F497D" FACE="Calibri">I will likely be using ATTiny8</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT COLOR="#1F497D" FACE="Calibri">4</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><FONT COLOR="#1F497D" FACE="Calibri"> to</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"> <FONT COLOR="#1F497D" FACE="Calibri">an I/O expander like:</FONT></SPAN><SPAN LANG="en-us"> </SPAN><A HREF="http://ww1.microchip.com/downloads/en/DeviceDoc/21952b.pdf"><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"><U><FONT COLOR="#0000FF" FACE="Calibri">http://ww1.microchip.com/downloads/en/DeviceDoc/21952b.pdf</FONT></U></SPAN><SPAN LANG="en-us"></SPAN></A><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
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<P DIR=LTR><SPAN LANG="en-us"><FONT COLOR="#1F497D" FACE="Calibri">I know I will need diodes across the solenoids to suppress the back EMF when they turn off.</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT COLOR="#1F497D" FACE="Calibri">I was not planning on any opto-isolation.</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT COLOR="#1F497D" FACE="Calibri">I will probably be using a lead acid battery to power the solenoids.</FONT></SPAN><SPAN LANG="en-us"></SPAN><SPAN LANG="en-us"></SPAN></P>
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<P DIR=LTR><SPAN LANG="en-us"><FONT COLOR="#1F497D" FACE="Calibri">Thanks.</FONT></SPAN></P>
<P DIR=LTR><SPAN LANG="en-us"><FONT COLOR="#1F497D" FACE="Calibri">---> Paul</FONT></SPAN></P>
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