<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div>On this topic of motor backlash / bouncing ground -- I'm confused due to recent experimentation :) Btw, this thread was really great stuff, thanks! I've been working on a first bot build which naturally is going slowly and roughly. :) The source of confusion is a BS2 resetting about 50 ms after it turns on a mosfet to drive a motor.</div><div><br class="webkit-block-placeholder"></div><div>Details: BS2 on a proto board powered by 9V batt, small brush DC motor (mabuchi FA130) powered by a 3V source (2xAA). I'm using a single NPN MOSFET (IRF510A if that matters) to power the motor.</div><div><br class="webkit-block-placeholder"></div><div>* One motor input is connected to +3V, and the other input to the Drain. </div><div>* The Gate is hooked to a pin on the BS2 and is also pulled down to ground thru a 10M resistor (err... I think so... maybe I took this out?). </div><div>* The Source going to a common ground</div><div>* The wires between the motor and the board are long (4"). The wires from the AA pack to the board are also long (5")</div><div><br class="webkit-block-placeholder"></div><div>I've tried running the Source pin to ground at the 3V battery input to the board, to the 9v batt (-) terminal, to the BS2's Vss pin, etc. None of these mattered; the BS2 reset shortly after attempting to power up the motor (versus turning it off as described in the thread). It would not reset with the motor disconnected but the 3V pack in place. The scope showed a voltage dip across the 3V pack as one might expect but didn't see any dip on the 9V batt. Wasn't sure what to look for as far as a bouncing ground until after I fixed it and came back and re-read this :)</div><div><br class="webkit-block-placeholder"></div><div>The fix was a 100uF electrolytic cap across Vdd to Vss on the BS2. (Vdd is regulated). I had a .1uF on hand for decoupling but it didn't do a thing... I have looked at the circuit (accursed wire wrap) over and over and can't find any wiring goof ups... </div><div><br class="webkit-block-placeholder"></div><div>Does this sound more like I've goofed the wiring and something is drawing too much current from Vdd (I don't see how but...)? </div><div><br class="webkit-block-placeholder"></div><div>Or is it some mystical inductive / EMF voodoo causing an apparent brown out / bouncing ground / etc. ? </div><div><br class="webkit-block-placeholder"></div><div>I'm at a loss to explain what is going on and thought I'd ask the gurus :)</div><div><br class="webkit-block-placeholder"></div><div>Many thanks!</div><div><br class="webkit-block-placeholder"></div><div>Michael</div><div> <span class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-align: auto; -khtml-text-decorations-in-effect: none; text-indent: 0px; -apple-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><span class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-align: auto; -khtml-text-decorations-in-effect: none; text-indent: 0px; -apple-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><span class="Apple-style-span" style="border-collapse: separate; border-spacing: 0px 0px; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; text-align: auto; -khtml-text-decorations-in-effect: none; text-indent: 0px; -apple-text-size-adjust: auto; text-transform: none; orphans: 2; white-space: normal; widows: 2; word-spacing: 0px; "><div>---</div><div><b style="font-weight: bold; "><font class="Apple-style-span" color="#646466"><font class="Apple-style-span" face="Arial Narrow"><span class="Apple-style-span" style="color: rgb(100, 100, 102); font-family: Arial Narrow; font-weight: bold; "><span class="Apple-style-span" style="color: rgb(100, 100, 102); font-family: Arial Narrow; font-weight: bold; ">Michael</span></span></font></font></b><font class="Apple-style-span" color="#646466"><font class="Apple-style-span" face="Arial Narrow"><span class="Apple-style-span" style="color: rgb(100, 100, 102); font-family: Arial Narrow; "><span class="Apple-style-span" style="color: rgb(100, 100, 102); font-family: Arial Narrow; "> Shimniok</span></span></font></font><font class="Apple-style-span" color="#000000"><font class="Apple-style-span" face="Arial Narrow"><span class="Apple-style-span" style="font-family: Arial Narrow; "><span class="Apple-style-span" style="font-family: Arial Narrow; "> - </span><font class="Apple-style-span" color="#66141C"><span class="Apple-style-span" style="color: rgb(102, 20, 28); font-family: Arial Narrow; ">1986 Jeep Grand Wagoneer "Troubled Child"</span></font><span class="Apple-style-span" style="font-family: Arial Narrow; "> - </span></span></font></font><font class="Apple-style-span" color="#181D9D"><b style="color: rgb(24, 29, 157); font-weight: bold; "><font class="Apple-style-span" face="Arial Narrow"><span class="Apple-style-span" style="color: rgb(24, 29, 157); font-family: Arial Narrow; font-weight: bold; "><span class="Apple-style-span" style="color: rgb(24, 29, 157); font-family: Arial Narrow; font-weight: bold; ">FSJ Blog @ </span></span><span class="Apple-style-span" style="font-weight: normal;; color: rgb(24, 29, 157); font-family: Arial Narrow; "><span class="Apple-style-span" style="color: rgb(24, 29, 157); font-family: Arial Narrow; "><span class="Apple-style-span" style="color: rgb(24, 29, 157); font-family: Arial Narrow; "><a href="http://tc.wagoneer.net">http://tc.wagoneer.net</a>/</span></span></span></font></b></font></div></span></span><br class="Apple-interchange-newline"></span> </div><br><div><div>On Jan 7, 2008, at 6:01 AM, Triffid Hunter wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">On Mon, 7 Jan 2008, <a href="mailto:DeltaGraph@aol.com">DeltaGraph@aol.com</a> wrote:</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><br></div> <blockquote type="cite"><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">OK, Chuck,</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">I think I am getting clued in.</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><br></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">So really more than IR drops due to loads we are talking inductive drops or</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">increases of voltage V=Ldi/dt depending on increasing or decreasing<span class="Apple-converted-space"> </span>current.</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><br></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">So for an instant, when relay opens and current in motor circuit decreases</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">very rapidly , Scott's ground lead looks like a battery supplying at least<span class="Apple-converted-space"> </span>a</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">few volts to the ground wire -- got it.</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><br></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">If per chance it supplied 5 volts, the voltage supply might drop to zero --</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">assuming no capacitance at processor.</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><br></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">This brings up a question. Could a reasonable capacitor say 10 uF tied to</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">processor (or real close)<span class="Apple-converted-space"> </span>protect processor from the bounce?</div> </blockquote><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><br></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">That's exactly what decoupling capacitors are for. Also remember that cmos chips only take low currents on average - that low current is taken in very very short sniffs of up to a few amps, and they *need* 100nF or so of high frequency capacitor as close to their power pins as possible to keep their voltage good. Even an inch or two of track introduces enough inductance to cause the chip issues. Ceramics are excellent for this, and MKTs should be acceptable. Electrolytics simply don't have the high frequency response to work here, although they work well in parallel with something that does.</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><br></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">A star grounding system can help too - where each separate section's ground is connected to a single physical point, so all voltages everywhere are relative to that point, and high current sections have no effect on the ground leads of low voltage ones.</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><br></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Remember, wires at right angles to each other have almost no coupling, whereas parallel wires have (relatively) good coupling. Keep this in mind when running any high current wires. Also, twisting wires with their corresponding grounds helps keep noise down as the currents (and hence fields) cancel.</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">_______________________________________________</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">DPRGlist mailing list</div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><a href="mailto:DPRGlist@dprg.org">DPRGlist@dprg.org</a></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><a href="http://list.dprg.org/mailman/listinfo/dprglist">http://list.dprg.org/mailman/listinfo/dprglist</a></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><br></div> </blockquote></div><br></body></html>