Avoiding electrical mistakes, Best way to do

Hello everybody,

I am an absolutely beginner and not so familiar with electronics.
Want kindly ask if you experts can help me avoiding mistakes.

My aim is to have a good A-B line following, u-turn at headland is not so important for me.
As i understood corretly the best place for GPS antenna is right above the front axis.
At my tractor the front part can rotate relativ to the back and cabin. Therefor I want to place the MMA8452 at the front in a small terminal box, the remaining parts inside a terminal box safely in the cabin.
Would this be a good way to go or not because of a long cable from MMA to Arduino, creating some errors or inteferrences?
Do i have to pay attention on cable and plugs?

In the main terminal box I want to place the BNO. Is there something special to observe? Has it to be shielded in some way?

As GNSS receiver I am going to use the C099 F9P as it has a built in bluetooth modul and standard antenna from u-blox.
Is it correct to place the antenna on a aluminum groundplate?

Thanks for your feedback in advance.
May this helps some beginners like me to avoid mistakes.

Sorry for bother you again,

to make above story short.
Could you please help if i have to pay special attention on cabels and plugs between:

  • WAS to ADS1115
  • MMA8452 to Nano
  • BNO055 to Nano
  • Phidgets to IBT2

ADS1115 and BNO055 (Adafruit) work with 5V. So I need step-down 12V to 5V
MMA8542(Sparkfun) works with 3.3 V so I need a second step-down 12V to 3.3V.

Do i need a step down in SDA/SCL line as they are all together connected to same Nano pin?

Some advantages using steel or plastic box placing all parts inside causing magnetig inteferrences or something else?

Thank you a lot in advance.


Use the 3.3V output of the Nano for power supply of the MMA, it’s done like this on the official PCB (see PCB schematic in support files here : https://github.com/farmerbriantee/AgOpenGPS/releases/download/4.1.12/Support_Files.zip).
For I2C bus, use a 330Ohm resistor in serial with SDA and SCL, is also done like this on the official PCB.

You also have all the datas in the Sparkfun MMA8452 guide : MMA8452Q Accelerometer Breakout Hookup Guide - learn.sparkfun.com


Thanks Math,

I see the resistors on the PCB wiring plan.
May a very stupid questions.
I saw a very simple wiring picture, i guess it was from Andreas O. so my plan was to wire everything with cables.
Do I really need all these resistors/capacitors shown on the PCB?



I thinks some people have done a direct wiring mounting based on the simple schematic available in the wiki. I have build my prototype like this (see here: Implement on a Fiat F100 success - #4 by Tooki57). Tests showed that It works, but du to external factors (rain and after confined in Paris du to CODID crisis), I haven’t test it in operationnal conditions.
But I also encountered a bug, essentially when AOG have to make wide drive corrections, that is probably du to bad power input regulation and filtrations of LM2596, see here: Access to the port 'COM4' is denied - #13 by Math.
So I can’t garantee you that this simple electronic assemblie would work: peraps someone who has this kind of assembly functionnal can attest here.

Most people here use a PCB, that add the resistors/capacitors you are talking about, for filtering and decoupling function. PCB assembly is clearly more robust.

But what ever electronics assembly way you choise, with Sparkfun MMA, you need the 330Ohm resistors on SDA and SCL. The simple assembly showed on the wiki use the MMA board from Adafruit, which can be power supplied with 5V, that why there insn’t resistor on SDA and SCL on this schematics.


I hace a related doubt, i built a box with the GPS Antenna and the ADS and BNO, im planning on puting It on front of the tractor (Its in the mechanic so i cant test It), being located there ive also put an input connector for the WAS on the box to connect It to the ADS, so the ONLY wires coming back to the cabin are VCC GND SDA & SDL, the question is would i encounter problems hay having that cable be 4 meter long?


Normaly, the I2C bus is limited to 1 or 2m wire in the best conditions.
In fact it depends of the capacitance of the wires.
You can add a i2c extender to extend the bus lenght.
Discussion about it also here:


i tried yesterday with a much longer (almos 10 meter) cat6 cable and it works pretty well, next week ill mount it in the tractor if i have it back and let you know how it works, ive looked to that extender and it might be a good choice if the regular connection fails somehow

@diegocesaretti it’s quite the same way i want to do it.
I want to place the MMA next to the GPS antenna so i have correct roll correction. Having the BNO there is also fine.
Guess you have a small terminal box with antenna mounted on top? Do you use a ground plate below antenna?
How have you connected the cat6?
VCC and GND also on it? Shield connected to GND?

Why do you want to place mma close to the antenna. Roll it the same all over the tractor as it react to gravity, except for articulated tractors where front and back are different off course. Same for bno055, just as far from magnetic field as possible.

I did exactly that, used a “Sándwich” ip67 eléctrical case, on the top half ive put a plate with the GPS Antenna, on the bottom half os the BNO, MMA, and a WAS input, connected to the ADS, (and a bluetooth board for the GPS), i use the 5v and GND comming from another case with the Arduino and IBT inside the tractor, and send back the i2c data from the ADS to the cab, while Its not installed on the tractor yet It seems to work fine as i Tested it with a very long Cat6 cable, It Will be much shorter, the boxes have DB9 conectors, o suspect ill have to change them for some kind of automotive waterproof connector

In my case i wanted to put the GPS on front of the tractor, and to keep It simple and converge everything in two cases just one cable i went with this setup, i use bluetooth all around and nothing is conected to the tablet but POWER, i did this because i find USB conections failing fue to vibrations before, ill try this method and if Its unstable (didnt seem unstable at all in testing so far) ill go with udp

I get your point, but I am concerned about the effects of sideways acelleration on the roll output. I know Brian have done a great job of filtering the output from the mma, so maybe it doesn’t matter.
I would prefer mma close to ground and antenna as high as necessary to avoid that cabin shadows for low satellites

@Larsvest I’m planning to position the gps antenna right above the front axis because i heard it would be best position for A-B following.
My tractor is a machine carrier. The front can rotate independant from the rear, so i dont want to put MMA inside the cabin.
Guess the MMA reacts quite sensitive and fast?
What about cabin suspension, does it affect?

@diegocesaretti You have a MMA working with 5V?

Adafruit one does 5v

Yes It works fine

I would like to ask if you use any protection against burning out the contacts in the control relays for additional solenoid valves. These are induction receivers and 10A relays controlled from arduino quickly
They sit down. In addition, the impulse that goes when disconnecting often causes a problem with disconnecting the USB ports. Would some kind of extinguishing system solve this problem? Do you also have similar problems?