Go Down

Topic: Filtering 5V and 12V in a noisy automotive environment (Read 4 times) previous topic - next topic

Krupski


I have a 5v wire that runs from my arduino along the frame of my truck to a switch at the rear and back.  I want to put a filter on the signal wire coming back just to filter out any spikes and noise that might be picked up by that wire, just to be safe.  How do I pick the capacitance value to use for this sort of application?

And if I wanted to filter a 12V hot line (presumably straight off the alternator) to get a cleaner 12V wire that I can later divide and use with Arduino input pin, what kind of capacitor and/or circuit would I use here?


One of the biggest "glitch" sources in an automotive power system is power drain spikes. To eliminate these, use a series diode and a capacitor to filter the incoming 12 volts. If a voltage drop spike comes along, the diode will block it and the capacitor will fill in the gap.
Gentlemen may prefer Blondes, but Real Men prefer Redheads!

DVDdoug

A capacitor alone doesn't do much, because there is so much current available in an automotive system to charge-discharge the capacitor.   The series diode with a small capacitor (maybe 1uF) should work very well for an Arduino input.  If you need to filter a 12V power supply, you'd probably want to increase the capacitor to 1000uF or more.   

A more "traditional" filter, is a series inductor, followed by a parallel capacitor to ground.    The larger the inductor and capacitor values, the more effective the filter.   The inductor has to be rated for whatever current is flowing through it to the load.       

sonnyyu


I have a 5v wire that runs from my arduino along the frame of my truck to a switch at the rear and back.  I want to put a filter on the signal wire coming back just to filter out any spikes and noise that might be picked up by that wire, just to be safe.  How do I pick the capacitance value to use for this sort of application?

And if I wanted to filter a 12V hot line (presumably straight off the alternator) to get a cleaner 12V wire that I can later divide and use with Arduino input pin, what kind of capacitor and/or circuit would I use here?


The item you need is Isolated DC - DC Converters. I saw tons of them when I was in Shenzhen.

http://arduino.cc/forum/index.php/topic,155946.msg1169500.html#msg1169500

db2db

An inductor, in series, and a 1200uf 35v cap to GND after that is what I've seen used for 12v filter.

sonnyyu

Isolated DC - DC Converters has Isolated DC voltage rating from few hundreds up to few thousands volts, plus it might have over voltage, over current, short circuit protection, and since it might run at few Mhz at switch circuit, all the car spikes and noise will be drop out.

Go Up