Jose, This was very useful and will get me going. I really needed this because=20 I don't yet have the self confidence when it comes to hardware to think=20 this out for my self but I can see the logic in it now when Ruben and=20 you put me on the right track. The stuff I am working on is some open hardware /software project for=20 home automation and control (=20 http://www.vscp.org/vscp/modules/index.html). I have been writing=20 hardware near software since the 80-th but this is my first public=20 project where I also do some hardware without having a hardware=20 engineer to blame for bad designed hardware. ;-) I will use plastic=20 boxes http://www.vscp.org/vscp/modules/kelvin_sht/images/camden.jpg for=20 the modules. So I have to come up with something else then a chassis for=20 the chassis gnd or maybe ground to the DIN rail will do?. Thanks again for much appreciated help and info. Cheers /Ake Jose Da Silva wrote: >On Thursday 03 February 2005 01:46 pm, Ake Hedman wrote: > =20 > >>my main problem appeared to be a ground problem just as Jim pointed out. >>I still need to follow you advices though for he final card. >> =20 >> > >Good to hear. > > =20 > >>I have no decoupling on the sensor lines today. Only on the power to th= e >>sensors. The sensor in this project gives out a square wave of 1 kHz - = 4 >>kHz and having a cap. on it will ruin the signal. >> =20 >> > >A)does it have to be a perfect square wave? Not likely >B)is it okay to degrade the square wave? Probably. Is 10% okay? Probably. > >...shoot for an RC or LC at about 40khz. That shouldn't affect your sign= al by=20 >very much. If you can make your RC or LC closer to 20khz, then even bet= ter. >Go for a combination of value RC or LC that only affects your circuit up= to=20 >1/10 at let's say 8 or 12 khz (for example, the fluorescent lights are=20 >running at approximately 90khz). > > =20 > >>Would something like Murata BLM21AG102SN1 >>(http://www.murata.com/catalog/c31/es0100.pdf) do this job? >> =20 >> > >Well, look at the values on the spec sheet. You have an inductor of abou= t=20 >10ohms at 100mhz, or 1 ohm at 10mhz or 0.1 ohm at 1mhz. in other words, = when=20 >you are dealing with maybe 100khz or 50khz, those beads really aren't do= ing=20 >more than costing you money. Leave the beads for cell-phone circuits at=20 >900mhz or higher. What you want will be better served with 10 ohm resist= ors,=20 >easier to find, cheaper too. > >Can your circuit handle 100 ohms instead of 10 ohm resistors? Then you w= ill=20 >have better immunity. >What type of circuit do you want to aim for? You mentioned you had to se= nd=20 >vcc to the sensor too, so you may want to aim for something like this: > >vcc--100R-+-100R-->to sensor vcc+ > | > 0.5u > | > chassisgnd > >gnd--100R-+-100R-->to sensor gnd- > | > 0.5u > | > chassisgnd > >input-100R-+-100R-- | > 0.25u > | > chassisgnd > >chassis---------->shield connection(only connect one side, not both) > >chassis is the metal box you put your circuit inside of. > >Perhaps the above is way overboard versus what you plan on doing, but gi= ves=20 >you a general idea of things. > >note, if we substituted a 390uH inductor, it would be roughly 100ohms at= =20 >40khz yet neglible at 4khz and far higher at higher frequencies. > > > =20 > >>I know I can=20 >>test this but just now I feel I need to hold the hand of someone who ha= s >>done this more than once.... >> =20 >> > >There is no hard/fast/rules I can point you towards. >I don't know anything about your sensor or your circuit. >I don't know if you are running on a battery circuit or an AC circuit. >I don't know if you are going to run this in the middle of a forest with= no=20 >local noise, or if you are going to run it within a setting full of=20 >hi-voltage motors generating lots of spark-noise spikes. >I don't know if you will be running this for your personal use, or for d= ry=20 >arid lighting-frequented areas. >I don't know if you will run it in a noisy environment such as a car=20 >ignition, boat ignition or general house noise or industrial factory=20 >location or close to a radio tower of one sort or another. >Far easier for you to work it out on your end versus me multiple guessin= g=20 >here. ;-) >Since you are in Europe (I think), then one or more of these will give y= ou an=20 >idea of what you are guarding your circuits against: >---------------------- >Immunity: IEC 1000=20 > EN55024 per EMC Directive 89/336/EEC, including=20 > IEC 61000-4-2 Electrostatic discharge immunity test=20 > IEC 61000-4-3 Radiated, radio-frequency, electromagnetic field immunity= test=20 > IEC 61000-4-4 Electrical fast transient/burst immunity test=20 > IEC 61000-4-5 Surge immunity test=20 > IEC 61000-4-6 Immunity to conducted disturbances, induced by radio freq= uency=20 >fields=20 > IEC 61000-4-8 Power frequency magnetic field immunity test=20 > IEC 61000-4-11 Voltage dips, short interruptions and voltage variations= =20 >immunity tests=20 > >Line Distortion: EN 61000-3-2 per EMC Directive 89/336/EEC=20 > >Voltage Fluctuations and Flicker: EN 61000-3-3 per EMC Directive 89/336/= EEC=20 >---------------------- >These people would like to have their components installed in your circu= it. >Some of the info is useful (TThe IEC61000 info is real-world problems to= =20 >consider... perhaps not useful where you live, but will certainly be use= ful=20 >in a dry-static-lightning environment) this doc seems to give you a gene= ral=20 >feel of IEC61000 >http://www.semtech.com/pdf/an96-07.pdf > >(they also have example circuits). >perhaps a page to start with.... look at the circuits here: >http://www.semtech.com/products/products_line_familydisplay.asp_Q_Family= ID_E_7_A_LineID_E_1 > >here is another circuit (see top of page 4): >http://www.semtech.com/pdf/stf701.pdf > > > =20 > >>Another path in on the board is the CAN bus which has a very long cable. >>Should I do the same thing there? >> =20 >> > >I have not looked at CAN, however, I would believe some CAN chip=20 >manufacturers will supply real sample circuits which you can model your=20 >circuit on while others may have sample circuits which have never gone=20 >beyond a "paper" example (in other words, not tested in real life). >You'll have to ask someone else with experience in this area then. > >Maybe the above is more info than you want, but hopefully useful :-) > >cheers! > =20 > --=20 --- Ake Hedman (YAP - Yet Another Programmer) eurosource, Brattbergav=E4gen 17, 820 50 LOS, Sweden Phone: (46) 657 413430 Cellular: (46) 73 84 84 102 Company home: http://www.eurosource.se =20 Kryddor/Te/Kaffe: http://www.brattberg.com Personal homepage: http://www.eurosource.se/akhe Automated home: http://www.vscp.org --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist