<div dir="ltr">Craig,<div><br></div><div>That circuit looks a little wonky. It seems they want to use the 2N3904 for voltage translation (the FET is not logic level sensitive, it is famous because you could buy it at Radio Shack) but they do not provide a ground reference for the emitter of the 2N3904, the emitter only connects to the FET's gate. </div><div><br></div><div>The BJT would turn on when the gate voltage (through the 4.7k resistor) reaches around 0.6V above the emitter voltage but the emitter voltage is floating with no ground reference. So if the circuit did turn on, it would pull the FET gate voltage up and turn on the FET. Turning off the FET has it's own issues though since there is no path to drain current from the FET gate, the FET will turn off in the semi random time it takes for the gate charge to leak away. You could make it work by putting a large resistor between the FET gate and GND but the FET would turn on faster than it would turn off. </div><div><br></div><div>It would be much more effective if you could use a more sensitive FET that could be driven directly from the logic pin (via a 1k or so resistor). This would let you drive current to turn on the FET as well as sink current to turn off the FET.</div><div><br></div><div>Note they are also missing a kickback diode across the load so you would be dumping nasty high frequency, high voltage spikes back into the power rail and eventually your chips will start acting oddly before dying. Do not skip the kickback diode, the body diode of the MOSFET does nothing to help tame the inductive kick when the FET is switched off.</div><div><br></div><div>Shane</div></div><br><div class="gmail_quote"><div dir="ltr">On Sun, Jan 8, 2017 at 12:20 PM Craig Cook via TriEmbed <<a href="mailto:triembed@triembed.org">triembed@triembed.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="gmail_msg"><div style="color:#000;background-color:#fff;font-family:HelveticaNeue-Light,Helvetica Neue Light,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" class="gmail_msg">Ah, learning more.  This is the project I am looking at:<div class="m_-9197090269050558210qtdSeparateBR gmail_msg"><br class="gmail_msg"><br class="gmail_msg"></div><div class="m_-9197090269050558210yahoo_quoted gmail_msg" id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22658" style="display:block"><div style="font-family:HelveticaNeue-Light,Helvetica Neue Light,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22657" class="gmail_msg"><div style="font-family:HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22656" class="gmail_msg"><div class="m_-9197090269050558210y_msg_container gmail_msg" id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22655"><div id="m_-9197090269050558210yiv0252341171" class="gmail_msg"><div id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22654" class="gmail_msg"><div style="color:#000;background-color:#fff;font-family:HelveticaNeue-Light,Helvetica Neue Light,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22653" class="gmail_msg"><div id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4592" class="gmail_msg"><br clear="none" class="gmail_msg"></div><div dir="ltr" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4593" class="gmail_msg"><a rel="nofollow" shape="rect" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4602" href="https://chip.hackster.io/user024507/motor-on-9c6bd1?ref=channel&ref_id=5276_trending___&offset=22" class="gmail_msg" target="_blank">https://chip.hackster.io/user024507/motor-on-9c6bd1?ref=channel&ref_id=5276_trending___&offset=22</a></div><div dir="ltr" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4603" class="gmail_msg"><br clear="none" class="gmail_msg"></div><div dir="ltr" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4607" class="gmail_msg">Is the 2N3904 working as an isolator?<br clear="none" class="gmail_msg"></div><div dir="ltr" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4627" class="gmail_msg"><br clear="none" class="gmail_msg"></div><div dir="ltr" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4819" class="gmail_msg">The donor truck contains these:</div><div dir="ltr" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4899" class="gmail_msg">BR8550D 064 (x 4)</div><div dir="ltr" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4900" class="gmail_msg">C1815Y 5L</div><div dir="ltr" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4901" class="gmail_msg">Super Chip STRX3A, 60100395<br clear="none" class="gmail_msg"></div><div dir="ltr" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4947" class="gmail_msg"><br clear="none" class="gmail_msg"></div><div dir="ltr" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_5047" class="gmail_msg">Could I reuse the C1815Y for my isolator?<br clear="none" class="gmail_msg"></div><div dir="ltr" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_6190" class="gmail_msg"><br clear="none" class="gmail_msg"></div><div dir="ltr" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_6269" class="gmail_msg">I also have these new PN2222ABU, BC547B, P2N2222AG<br clear="none" class="gmail_msg"></div><div dir="ltr" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_6284" class="gmail_msg"><br clear="none" class="gmail_msg"></div><div dir="ltr" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_6471" class="gmail_msg"><div id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22699" class="gmail_msg">I could attach a picture of donor truck board, but it would have to be less than 100k.</div></div><div dir="ltr" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_6486" class="gmail_msg"><br clear="none" class="gmail_msg"></div><div dir="ltr" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4686" class="gmail_msg">Thanks</div><div dir="ltr" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4817" class="gmail_msg"><br clear="none" class="gmail_msg"></div><div dir="ltr" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4675" class="gmail_msg">Craig<br clear="none" class="gmail_msg"></div><div class="m_-9197090269050558210yiv0252341171qtdSeparateBR gmail_msg" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4594"><br clear="none" class="gmail_msg"></div><div class="m_-9197090269050558210yiv0252341171yahoo_quoted gmail_msg" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4598" style="display:block">  <div id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4597" style="font-family:HelveticaNeue-Light,Helvetica Neue Light,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" class="gmail_msg"> <div id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4596" style="font-family:HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" class="gmail_msg"> <div dir="ltr" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4595" class="gmail_msg"> <font id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4599" size="2" face="Arial" class="gmail_msg"> </font><div class="m_-9197090269050558210yiv0252341171yqt8182019916 gmail_msg" id="m_-9197090269050558210yiv0252341171yqtfd80257"></div></div></div></div></div></div></div></div></div></div></div></div></div></div><div class="gmail_msg"><div style="color:#000;background-color:#fff;font-family:HelveticaNeue-Light,Helvetica Neue Light,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" class="gmail_msg"><div class="m_-9197090269050558210yahoo_quoted gmail_msg" id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22658" style="display:block"><div style="font-family:HelveticaNeue-Light,Helvetica Neue Light,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22657" class="gmail_msg"><div style="font-family:HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22656" class="gmail_msg"><div class="m_-9197090269050558210y_msg_container gmail_msg" id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22655"><div id="m_-9197090269050558210yiv0252341171" class="gmail_msg"><div id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22654" class="gmail_msg"><div style="color:#000;background-color:#fff;font-family:HelveticaNeue-Light,Helvetica Neue Light,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22653" class="gmail_msg"><div class="m_-9197090269050558210yiv0252341171yahoo_quoted gmail_msg" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4598" style="display:block"><div id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4597" style="font-family:HelveticaNeue-Light,Helvetica Neue Light,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" class="gmail_msg"><div id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4596" style="font-family:HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" class="gmail_msg"><div dir="ltr" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4595" class="gmail_msg"><div class="m_-9197090269050558210yiv0252341171yqt8182019916 gmail_msg" id="m_-9197090269050558210yiv0252341171yqtfd80257"><hr size="1" class="gmail_msg"> <b class="gmail_msg"><span style="font-weight:bold" class="gmail_msg">From:</span></b> Carl Nobile <<a href="mailto:carl.nobile@gmail.com" class="gmail_msg" target="_blank">carl.nobile@gmail.com</a>><br clear="none" class="gmail_msg"> <b class="gmail_msg"><span style="font-weight:bold" class="gmail_msg">To:</span></b> Craig Cook <<a href="mailto:cncook001@yahoo.com" class="gmail_msg" target="_blank">cncook001@yahoo.com</a>> <br clear="none" class="gmail_msg"><b class="gmail_msg"><span style="font-weight:bold" class="gmail_msg">Cc:</span></b> TriEmbed <<a href="mailto:triembed@triembed.org" class="gmail_msg" target="_blank">triembed@triembed.org</a>><br clear="none" class="gmail_msg"> </div></div></div></div></div></div></div></div></div></div></div></div></div></div><div class="gmail_msg"><div style="color:#000;background-color:#fff;font-family:HelveticaNeue-Light,Helvetica Neue Light,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" class="gmail_msg"><div class="m_-9197090269050558210yahoo_quoted gmail_msg" id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22658" style="display:block"><div style="font-family:HelveticaNeue-Light,Helvetica Neue Light,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22657" class="gmail_msg"><div style="font-family:HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22656" class="gmail_msg"><div class="m_-9197090269050558210y_msg_container gmail_msg" id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22655"><div id="m_-9197090269050558210yiv0252341171" class="gmail_msg"><div id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22654" class="gmail_msg"><div style="color:#000;background-color:#fff;font-family:HelveticaNeue-Light,Helvetica Neue Light,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22653" class="gmail_msg"><div class="m_-9197090269050558210yiv0252341171yahoo_quoted gmail_msg" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4598" style="display:block"><div id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4597" style="font-family:HelveticaNeue-Light,Helvetica Neue Light,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" class="gmail_msg"><div id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4596" style="font-family:HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" class="gmail_msg"><div dir="ltr" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4595" class="gmail_msg"><div class="m_-9197090269050558210yiv0252341171yqt8182019916 gmail_msg" id="m_-9197090269050558210yiv0252341171yqtfd80257"><b class="gmail_msg"><span style="font-weight:bold" class="gmail_msg">Sent:</span></b> Sunday, January 8, 2017 11:10 AM</div></div></div></div></div></div></div></div></div></div></div></div></div></div><div class="gmail_msg"><div style="color:#000;background-color:#fff;font-family:HelveticaNeue-Light,Helvetica Neue Light,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" class="gmail_msg"><div class="m_-9197090269050558210yahoo_quoted gmail_msg" id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22658" style="display:block"><div style="font-family:HelveticaNeue-Light,Helvetica Neue Light,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22657" class="gmail_msg"><div style="font-family:HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22656" class="gmail_msg"><div class="m_-9197090269050558210y_msg_container gmail_msg" id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22655"><div id="m_-9197090269050558210yiv0252341171" class="gmail_msg"><div id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22654" class="gmail_msg"><div style="color:#000;background-color:#fff;font-family:HelveticaNeue-Light,Helvetica Neue Light,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22653" class="gmail_msg"><div class="m_-9197090269050558210yiv0252341171yahoo_quoted gmail_msg" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4598" style="display:block"><div id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4597" style="font-family:HelveticaNeue-Light,Helvetica Neue Light,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" class="gmail_msg"><div id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4596" style="font-family:HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" class="gmail_msg"><div dir="ltr" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4595" class="gmail_msg"><div class="m_-9197090269050558210yiv0252341171yqt8182019916 gmail_msg" id="m_-9197090269050558210yiv0252341171yqtfd80257"><br clear="none" class="gmail_msg"> <b class="gmail_msg"><span style="font-weight:bold" class="gmail_msg">Subject:</span></b> Re: [TriEmbed] Pinewood derby help<br clear="none" class="gmail_msg">  </div></div></div></div></div></div></div></div></div></div></div></div></div></div><div class="gmail_msg"><div style="color:#000;background-color:#fff;font-family:HelveticaNeue-Light,Helvetica Neue Light,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" class="gmail_msg"><div class="m_-9197090269050558210yahoo_quoted gmail_msg" id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22658" style="display:block"><div style="font-family:HelveticaNeue-Light,Helvetica Neue Light,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22657" class="gmail_msg"><div style="font-family:HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22656" class="gmail_msg"><div class="m_-9197090269050558210y_msg_container gmail_msg" id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22655"><div id="m_-9197090269050558210yiv0252341171" class="gmail_msg"><div id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22654" class="gmail_msg"><div style="color:#000;background-color:#fff;font-family:HelveticaNeue-Light,Helvetica Neue Light,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" id="m_-9197090269050558210yui_3_16_0_ym19_1_1483893213641_22653" class="gmail_msg"><div class="m_-9197090269050558210yiv0252341171yahoo_quoted gmail_msg" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4598" style="display:block"><div id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4597" style="font-family:HelveticaNeue-Light,Helvetica Neue Light,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" class="gmail_msg"><div id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4596" style="font-family:HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif;font-size:16px" class="gmail_msg"><div class="m_-9197090269050558210yiv0252341171yqt8182019916 gmail_msg" id="m_-9197090269050558210yiv0252341171yqtfd49340"> <div class="m_-9197090269050558210yiv0252341171y_msg_container gmail_msg" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4652"><br clear="none" class="gmail_msg"><div id="m_-9197090269050558210yiv0252341171" class="gmail_msg"><div id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4651" class="gmail_msg"><div dir="ltr" id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4650" class="gmail_msg">Yes, you will need something like a MOSFET to handle the higher current that the motor will draw and a different power souce that what is being used for the CHIP, but that won't isolate the motor from the electronics. You will still need an opto isolator.<div id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4672" class="gmail_msg"><br clear="none" class="gmail_msg"></div><div id="m_-9197090269050558210yiv0252341171yui_3_16_0_ym19_1_1483893213641_4649" class="gmail_msg">~Carl<br clear="none" class="gmail_msg"></div></div></div></div></div> </div></div></div></div></div></div></div></div></div></div></div></div></div>_______________________________________________<br class="gmail_msg">
Triangle, NC Embedded Computing mailing list<br class="gmail_msg">
<a href="mailto:TriEmbed@triembed.org" class="gmail_msg" target="_blank">TriEmbed@triembed.org</a><br class="gmail_msg">
<a href="http://mail.triembed.org/mailman/listinfo/triembed_triembed.org" rel="noreferrer" class="gmail_msg" target="_blank">http://mail.triembed.org/mailman/listinfo/triembed_triembed.org</a><br class="gmail_msg">
TriEmbed web site: <a href="http://TriEmbed.org" rel="noreferrer" class="gmail_msg" target="_blank">http://TriEmbed.org</a><br class="gmail_msg">
</blockquote></div>