Shielding my project from electromagnetic noise in a modern vehicle?

Thread Starter

AGrayson84

Joined Jan 4, 2018
20
Good morning/afternoon/evening everyone. I am finishing off coding and building my prototype for a project I started a few weeks ago. I am bench-testing it now, but will be wiring it into my car in the next week or so, and wanted to prepare protecting my project from all the noise that it may see once installed.

I am fresh to working with micro-controllers, and small electronics in general, so I apologize in advance if I'm too vague about anything specific in this, and also apologize about my lack of detailed knowledge on this topic. I have an ATMega328 ICU on my board, and I'm running 12v power into the board, but regulated down to 5v using a 7805 regulator, with capacitors on each leg of the regulator. I am tapping into the output wiring of the following 0-5 volt sensors/switches, which are each individually ran into the analog inputs of the board: throttle position sensor (TPS), fuel pressure sensor, manifold absolute pressure (MAP) sensor, air-to-fuel ratio (AFR), oil pressure.

Going to one of my digital inputs is a 5v square wave pulse coming from the "tach" output on the PCM, so I can also monitor the RPM of the engine. Based on certain values I have stated in several conditions, ie: If (TPSvoltage > 2.5 & FuelPressurevoltage < 1.0), a digital output on the ICU will trigger a 12v pulse (via an opto-coupler) to an external, aftermarket rev limiter, to bring the engine down to a much lower RPM until the condition is no longer true, for example.

I will be using 22 AWG wire to and from the sensors/switches, as well as for ground and power from the vehicle's battery to the PCB.

Regarding electromagnetic noise, I am totally unfamiliar with where, specifically, I may be seeing it on my project (the wiring running to/from the sensors, within the plastic enclosure that will be housing the PCB and stored in the interior of my car, or what. I tried doing some general research on the topic, to understand where I might be seeing the noise, and what can be done to shield it, but either I'm just not finding a good source that is easy to understand, or maybe there truly just isn't any solid information out there on shielding micro-controllers from noise in vehicles. If anyone is in need of more information to provide assistance with this please let me know and I will provide that ASAP. Any help would be greatly appreciated!! :)

-Andrew
 
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Twisting reduces EMI. Shielding reduces RFI. Shields connect at one end only. Preferably the source.

It's in your best interest to avoid ground loops.

Cars sensors are generally referenced to he supply voltage (e.g +5). They are ratiometric

The car environment is NASTY. http://m.littelfuse.com/~/media/ele...n_automotive_environment_application_note.pdf

Look at Linear technology Surge Stopper line of products.

Watch the input levels Usually they are something like -0.3 to Vdd+0.3. Bad things happen when Vdd is zero or not powered on. Some "Over the top" OP amps/comparators may help you. They allow inputs much greater than the supply voltage.

Watch your ground references.
 

Thread Starter

AGrayson84

Joined Jan 4, 2018
20
Thank you both very much for your responses!!


Twisting reduces EMI. Shielding reduces RFI. Shields connect at one end only. Preferably the source.

It's in your best interest to avoid ground loops.

Cars sensors are generally referenced to he supply voltage (e.g +5). They are ratiometric

The car environment is NASTY. http://m.littelfuse.com/~/media/ele...n_automotive_environment_application_note.pdf

Look at Linear technology Surge Stopper line of products.

Watch the input levels Usually they are something like -0.3 to Vdd+0.3. Bad things happen when Vdd is zero or not powered on. Some "Over the top" OP amps/comparators may help you. They allow inputs much greater than the supply voltage.

Watch your ground references.
I'm going to have to be totally honest here.... I have little idea what any of this means. Haha. I definitely have a lot of learning to do, so I'm going to spend some time later this evening researching the terms you mentioned and making some sense of it. It's not you, it's me :) Thanks a bunch and I'll let you know if I can make heads or tails of it :)



Those wires had better be screened!
You will need to protect your gizmo against load dump spikes (both positive and negative).
Thanks Alec. The wires are not screened/shielded. I can certainly purchase some screen wire for the project, and not to challenge you at all when I ask this... I'm just trying to get a grip on using electronic projects in cars. So my question is how would something like the device below not require shielded wiring and such? I ask because I'd like to keep the project as clean as the one below, just running plain automotive-grade wire if possible. I suppose there it a micro-controller embedded in the enclosure, but that's only an assumption.

The below controller intercepts the ignition coil circuits and limits the RPM to the an RPM depicted by the integral DIP switches, and can also retard the timing of the engine using the integral DIP switches. The other connector (orange) connects to a MAP (manifold absolute pressure) sensor. Is there a way to keep my project this simple and clean, or is there something extremely different about my project that prevents me from mimicking something like this?




Sorry for my ignorance again..... I'm just trying bring my project to fruition on my car ASAP. Thanks again everyone! :)
 
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