Filtering supply lines

Oliver Scholz SOZ at iis.fhg.de
Fri Jul 19 06:59:36 GMT 1996


> This sounds like a grounding problem.  Brake lights are non-inductive, so it
> is unlikely they are generating "spikes".  Try running your ground wire

Yes, but the brake pedal also activates the cruise control solenoid,
which is inductive...

> directly back to the battery.  Grounding to the chassis might cause problems
> with "ground bounce" when you activate high current loads.

All ground wires go to the same point on *my* circuit board...
only that ground is connected to the ground...
  
> Phillips and Panasonic both make a small 3 terminal "noise filter" device
> into the (metal) box.  They won't affect most digital signals.  Panasonic
> p/n ELK-AH103EB ($.90) or EXC-ECT223ZVT ($.20)
Sounds good. That together with a shielded cable might just do the trick!

> This is probably your best bet in terms of power supply, but it won't help
> if your noise is coming in on a signal lead.  National's "Simple Switcher"
> p/n LM2574N-5.0 is a nice little chip, 6-60V in, 5V @ 500 mA out, in an 8
> pin DIP package, and it only requires 2 caps, a small stock value inductor,
> and a diode. Can't get much smaller than this.  National has a web page
> where you can request free samples.  Can't get much cheaper than this, either.

I do have some friends who are interested in my little gadget as well,
so I would need a few more parts than just one or two samples.
The low drop linear regulators are more readily available...

I will try the shielded cables and pi filters on the signal line first,
since I believe that is more probable (after all, the  rest of the circuit
works just fine, no  crashes...)

Thanks,

-Oliver




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