Too much noise in Embedded system?

Too much noise in "Embedded" system?

Hey everyone. I'm working on putting a circuit board (with microprocessor, eventually) into a car for electro-pneumatic shifting on a manual transmission. This means that the circuit has to run on a 12V source being charged by an alternator.

I have a design for the circuit in Visio, and I was just wondering if there was going to be too much noise in the circuit. I know that previous iterations had too much, but will it affect this particular circuit?



Last edited:
Re: Too much noise in "Embedded" system?

Oops! I put "12V source charged by a battery" I meant "12V source charged by an alternator"

Should make more sense now :P
Re: Too much noise in "Embedded" system?

Automotive electrical systems are notorious for having large amounts of noise due to the ignition system. Chances are, unless you include some type of filtering, you will have noise issues especially if power is taken directly from the alternator.

Why is your "upshift" button breaking the ground on your ECU ignition signal? Why is this even included in your circuit?
Re: Too much noise in "Embedded" system?

Ergh..? I'm a first year Engineering student... I have no knowledge of "filtering" systems (you mean like a capacitor ... somewhere?) :( Anything you can explain would be most excellent :P

Ignition Gnd:
It's a quick and dirty way of stopping the engine for a brief period of time while we shift gears... I forget exactly why, something to do with not putting too much strain on the engine. It's just like taking your foot off the gas when you shift, I guess.

I was told a series of requirements for this circuit, and copied its functionality directly from what we currently have using relays...
Re: Too much noise in "Embedded" system?

I did a bit more digging into what the previous problems had been. Turns out there is enough filtering when the alternator is converted to DC and passed through the battery that it doesn't really effect the system. More damaging, however, was the starter motor creating ridiculous magnetic fields that were causing the car systems (including the shifter controller) to do strange things... like shift gears :P

Turns out I just need some serious shielding! Thanks for the help, though :)
Last edited:

The Physics Forums Way

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving