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Topic: Filtering 5V and 12V in a noisy automotive environment (Read 15122 times) previous topic - next topic


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?

It depends of course on your particular application, but are you not trying to solve a problem where none exists?

I discovered Arduino because of this very problem: noise in an automotive application.

A year or so ago I made a little electronic device for my 45 year old car, using what is called a 555 timer.  In case you don't know, this is an 8-pin IC chip that became available in the 1970's, when IC chips had just started to appear on the market.  On the workbench and in the car (with the engine not running) the circuit worked perfectly.  But when the engine was running the circuit did weird things.  I tried everything to try and isolate the circuit from noise - ceramic capacitors, electrolytic capacitors, inductors, metal shields, in every possible combination.  Nothing worked.

I then trawled the internet and discovered that it was a well-known problem with the 555-timer in automotive applications - called "false triggering".  Somewhere someone made the comment that he had given up on 555-timers because of that, and had switched to microcontrollers.  What are those? I asked myself.

I then happened to see an Arduino in a shop, bought one, and got hooked.

I have since implemented the circuit with an ATtiny85 chip (for which I wrote the code on my Arduino) and it has worked faultlessly ever since.  The circuit was much simpler than the one I had built previously, and I used NO capacitors whatsoever.  I power the ATtiny from the car's 12 volt battery simply via an 820 ? resistor and a 5 v zener diode to earth.


Apr 10, 2013, 03:28 pm Last Edit: Apr 10, 2013, 05:05 pm by sonnyyu Reason: 1
This might be not the case, OP solve the 5v problem and facing 12v only.

few plans for OP;-

plan A
Power Supply Filter, L-C Type. It is cheaper and simpler, and worth to try first. ( credited by db2db )

plan B
Isolated DC-DC converter. offer additional protection and higher noise reject rate.

plan C
Wireless power technology, it might be worth to note on calendar since you might need to wait few more months.
It offers the possibility of "cutting the last cord", thereby removing the last remaining wired connections required to power and
recharge.  It is base on similar technology as Isolated DC-DC converter and noise reject rate is great. Now you need to make sure Arduino design is wireless and power cable is last cord.


I rigged a basic power supply some time ago. Basically a choke for both ground and hot, a cap in between, and a resistor and zener to ground to take out any load dumps.  I can't remember the values, but it seemed to work pretty well.

My concern was 60Hz and up interference; google for LC circuits to get an idea of the values.

Use components that are rated for at least 75VDC as load dumps can spike that high.

It's important to filter ground as well if you can.

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