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/iframe></center><br><br> <br><br> </center> </td></tr> </table> <center> <table> <tr> <td width="600"> <center><hr width="400"><font size="2"><b>The <a href="http://www.cyber-spy.com/">Cyber-Spy.Com</a> Usenet Archive Feeds Directly<br>From The Open And Publicly Available Newsgroup<br>Sci.Electronics.Design<br><br>This Group And Thousands Of Others Are Available<br>On Most IS NNTP News Servers On Port 119.<br><br><a href="http://www.cyber-spy.com/">Cyber-Spy.Com</a> Is NOT Responsible For Any Topic,<br>Opinions Or Content Posted To This Or Any Other<br>Newsgroup. This Web Archive Of The Newsgroup And<br>Posts Are For Informational Purposes Only.<br><br></b></font><hr width="400"></center> <center><font size="2"><pre><b> From: "Jeff Verive" <jeff.verive@tellabs.com> Newsgroups: sci.electronics.design References: <BZ0Q9.502408$WL3.129771@rwcrnsc54> Subject: Re: Automotive circuit falsing - urgent help needed please X-Newsreader: Microsoft Outlook Express 6.00.2800.1106 Message-ID: <AfkQ9.19$rt4.18063@news.uswest.net> Date: Tue, 31 Dec 2002 11:14:08 -0600 NNTP-Posting-Host: 138.111.168.64 NNTP-Posting-Date: Tue, 31 Dec 2002 11:14:08 CST At least four types of "filters" must be employed in an automobile: - Circuit-level and device-level power supply filtering - I/O conditioning (at the sensor, cable, and micro) - Circuit-level EMI protection (from radiated noise in the auto environment) - Circuit-level EMI reduction (making sure your circuit does not radiate or conduct outward excessive EMI) For the hobbyist, the most important things to cover are the power supply filtering and I/O conditioning. You want to ensure that under all circumstances (including ignition, jump-starting, alternator load-dumps, etc.) the circuit is protected from damaging high voltage and reverse voltage spikes, in addition to regulating the power supply voltage so that it is rock-solid under all of these conditions. All the signal conditioning in the world will not help if the micro is constantly getting reset or damaged by EMI. Proper fusing, over-voltage clamps, and generous use of L-C filters is best. In fact, it is a good idea to treat the power supply protection as a separate circuit, not just a few capacitors and diodes. National Semiconductor once sold a handbook on voltage regulators, and the section on automotive power filtering was outstanding. I bought this handbook, and keep it in a safe spot to keep other engineers from borrowing it indefinitely. I/O conditioning usually consists of low-pass or high-pass filtering (depending on the type of sensor), usually communicating with the micro via a shielded, twisted pair cable. The shield is *usually* grounded at the micro, to ensure that the shield does not act as an antenna. The twisted pair goes a long way toward rejecting differential mode noise, and a common mode choke near the micro helps remove common mode noise. I have almost always used differential mode and common mode filtering, along with opto-isolators to protect the micro. To protect from radiated EMI, consider using a faraday shield around the micro, with feed-through capacitors as part of I/O connections. A good PI or T filter network on the power supply and I/O will also keep you from conducting or radiating excessive EMI to other electronic circuits within the auto. Good luck, and remember to test, test, and test again. Jeff "MikeB." <mbrunton@ecagroup.com> wrote in message news:BZ0Q9.502408$WL3.129771@rwcrnsc54... > (Posted this in the other group but no articles show in the last 12 hours - > I probably should have put it here. Any comments welcome!) > > Hello gents, > > I recently made an automotive circuit that needs to detect such things as > when the brakes and turn signals are applied, when the wipers are turned on, > etc. This data is fed into an Atmel for processing. I'm having a problem > with the unit falsely detecting that the brakes or blinkers have been > activated. The things I have tried to fix it have not worked. > > From looking at the factory wiring diagram, the brake circuit is simply a > momentary switch inline with the brake circuit. There are no relays or > electronics in the circuit. From the diagram, there should be no power in > the line, and when the brake is applied (switch closes) power flows through > the switch and the brake light, illuminating the light. > > On the pin of the Atmel, I have an NPN transistor and I have the base > connected to the brake line through a 12K resistor such that when the > transistor is switched, the pin on the Atmel is grounded. When I try it out > on my bench it works fine - when power is applied to the "sensor" wire, the > Atmel correctly notes the signal. I've used this same setup on many Atmel > projects and haven't before run into a problem. When installed on the > vehicle however, it thinks the brakes are being applied even when they > aren't. I've tried this on several vehicles and even multiple units of the > same vehicle and it's erratic. Sometimes it detects it correctly, some > times it doesn't. > > I tried using a reverse-biased 5-volt Zener, so that it would take >5V to > switch the transistor. It did not seem to help, and the Atmel is still > acting as if the brake is being applied even when it is not. Can there > really be >5V of "noise" in the lines? > > Does anyone have any ideas? What sort of "filter" should I put on this line > to prevent the circuit from falsely tripping? I know automotive electrical > systems are very "noisy" and I'm assuming it's this noise that is falsely > triggering the circuit. I figured the zener with the resistor would do the > job, but it hasn't. What should I use to prevent the falsing? > > Thanks in advance for your insight... > > Regards, > Mike > > </b></pre></font><hr width="650"><a href="http://www.cyber-spy.com/electo-index.html"><font size="3">Go Back To The <a href="http://www.cyber-spy.com/">Cyber-Spy.Com</a><br>Usenet Web Archive Index Of<br>The sci.electronics.design Newsgroup</font></a><br><br></center></td><img src="http://cyber-spy.com/cgi-bin/livecntr.pl?0+1+unetsci" width="1" height="1" alt="The Cyber-Spy Toolkit - powerful internet spy software - live police scanners - usenet fbi secrets archive - newsgroup spy electronics archive - search engine spy tools - download TCST today!"> </tr> </table> </center> <center> <br><center><hr size="3"></center> <table width="100%" cellpadding="0" border="0" cellspacing="0"> <tr> <td align="left" valign="top"><small><b><i><a href="http://www.cyber-spy.com/index.html">Cyber-Spy.Com Live Resources</a></i></b></small></td> <td align="right" valign="top"><small> Copyright Alpha Omega Delta,<br> All rights reserved. </small></td> </tr> </table> <center><hr size="3"></center> <br><br> <br><br></center> </body></html>