I'm using an Arduino to manage a master warning system in an homebuilt airplane (a Longeze).
The problem I'm having is that adding the Arduino (more precisely, a Pololu a-star 32u4 SV Mini) powered directly from ship power (12V), creates enough RF noise to break squelch on the Comm radio.
I've tried simply adding various capacitor values from the Arduino power input to ground with no effect.
This particular Arduino accepts 5-40 volts. Bypassing the 12V ship power and using a separate USB power supply to power the microcontroller eliminates the issue (but creates different wiring problems).
Looks like they have a new version with an improved regulator. Anyways, with either one, I think its best to power with 6V to 7.5V if you can, as this greatly increases the current that can be delivered from the regulator.
I'm thinking the source of the noise is the switching regulator ... if it can't be reduced to acceptable levels with a lower voltage input, then maybe try an EMI/RFI coated enclosure, or use an external 12V-5V linear converter and connect to 5V or USB 5V on your board.
Switching regulators/power supplies always radiate noise. Even those the manufacturer insists do not do it. Many times it is radiated by the "ground" part of the circuit. That is because the generated square wave also is part of the ground current.
As the regulator is part of the printed circuit board, you don't have much choice other than completely enclosing the controller in a shielded enclosure and feeding power and ground out through separate filtered conductors. Outside the enclosure, the ground can now be made part of the rest of the plane's electrical ground.
First step is to switch to a linear regulator to provide 5V from the 12V supply. Build the unit into a diecast box and bolt the regulator to it for heatsinking. Ground the box via a strap to a low impedance point either in the airframe or to the 12V battery negative.
Not surprizing if there's no shielding for the board. Metal box, ferrite beads on the leads, are the
first precautions to try. An LC filter on the power in is probably wise.
The only capacitors that might have any effect are 100pF to 1nF ceramic, as these handle high frequencies,
and are available as feed-through types.
The frequency is relevant to choosing shielding measures. This sort of wavelength will mainly be
radiated from the wiring, which may be at resonant lengths, so those ferrite bead suppressors and
CLC filters are important things to try.
RFI compliance costs money and is rarely done for hobby components or self-built projects, but
here you need perhaps to find someone able to do some pre-compliance testing and figure out
the suitable mitigation.
You could also try using a 7808 linear regulator from the 12V supply to help isolate RF (it won't
be perfect, capacitance allows some to sail straight through)
I'll be out in the hangar again today working on it. I'm going to bring my scope and see if I can "see" the noise, to get an idea of the frequency and amplitude.
Building a small metal enclosure for the device isn't out of the range of possibility, but what will likely be a better and easier option is to use an off the shelf USB 12V converter. We've tried one of these, and despite having their own buck converters, they don't seem to create the same noise.
To Mark T - yup, I should have thought harder about the size of the caps I tried - I was in the 10s or 100s of microfarads range, not the picofarad range. Duh.
To all the other suggestions, including ferrite beads - thanks! Those are good ideas.
I'll post what I can see with the scope. Thanks again to all!
velocitypilot:
To Mark T - yup, I should have thought harder about the size of the caps I tried - I was in the 10s or 100s of microfarads range, not the picofarad range. Duh.
Such capacitors are more inductive than capacitive at these frequencies. Google "self-resonant frequency"
So I scoped the power today, and the Arduino is generating lots of noise... about 800 MV of noise on a 12V signal (!). And, the wave packet shown in the attached scope picture repeats at 125 Mhz - essentially right in the middle of the aviation VHF band.
I went ahead and installed the board from a cheap cigarette lighter USB adapter to power the Arduino. Problem solved. But geez, that's a bunch of noise!
800 megavolts is indeed a lot. Perhaps you mean millivolts?
E exa
P peta
T tera
G giga
M mega
k kilo - the only > 1 multiplier with a lower case symbol (because it clashes with K for kelvin)
m milli
ยต micro
n nano
p pico
f femto
a atto
To MarkT .... HA! Wow... that, sir, is a megaTYPO!
Yea, I blew that one!
To show how much of an idiot I am ... it turns out that I'm a retired EE ... I should have thought harder about several of these issues (like the size of the capacitor). I guess I was looking for an easy way out, and I had what I had at hand in the hangar.
I've been building airplanes for many years (decades). I guess I've forgotten too much of my Electrical Engineering training!
Thanks again to all! Sorry for the dumb questions!
