'Dirty' 12v power input filter sanity check

Link to the full project here > Diesel Glow Plug Controller

Hello Everyone,

So I have yet another one of those automotive projects and am asking a question that has seemingly been asked many times before. Despite doing some reading, it seems most of the topics do not come to a conclusive end although I did find one in particular that does have a schematic that is very similar to the one I am looking to create.

My goal of this post is to have the community verify my circuit design as feasible or if there is a glaring error then I would obviously like to correct so as to achieve a highly reliable setup.

Quick background, I am using an Arduino Nano Everything as a relay controller. It will have multiple inputs and a couple outputs. Ultimately it takes in inputs, makes a decision and outputs a signal to control a single automotive grade 12v 75A relay.

I am trying to work with one circuit at time to make sure each circuit is designed correctly. This is for a road going vehicle so it cannot be experimental, should have an expected lifespan of 5 years and not require any user intervention once put into service. That is the goal anyways.

Alright onto the circuit in question. This is the main power source for the Arduino. This is a Ignition 'Key On' circuit and will remain powered anytime the key is turned to the one position. This could be a span of seconds to hours, once the key on signal is sent to the arduino, it will execute its program until the key on power is removed.

I have a Shottky diode to protect against reverse polarity, a 220uF electrolytic cap to provide 'smoothing' of the signal, a 0.01uF ceramic disk cap to provide EMI suppression. I also have 20v zeenies available, but was unsure as to how or even if I needed to incorporate them.

Please, if responding, include part numbers if your going to recommend components. 'Just use a so and so from Amazon' is not helpful, nor is public opinion. Either yes, this checks out or no, you have x correct but y is dodgy and you really need component z to make this correct are the kind of responses I am hoping for. Thank You all in advance, your experience is appreciated.

I have updated the final schematic here, note that in the schematic, MPM3610 refers to the DC/DC converter built into the Arduino Nano Every. MPM3610 Data Sheet
Also I have ChatGPT verification of proper power filter circuit design, because I read it on the interwebs! See post #70

Here is the updated final schematic so you don't have to read through 70+ posts. Many thanks to all those that participated in this awesomely long thread. Everyone contributed something positive and I am appreciative of that. Thanks to everyone who participated! :heart:

Some people recommend an external 5V voltage regulator and that's probably the "safest" solution. You should use an external regulator if you need to power much more than the Arduino at 5V because the current capability of the built-in 5V regulator is limited.

You'll need a relay driver in any case but if your relay has a 12V coil so it doesn't need current at 5V you'll probably be OK.

The built-in regulator provides quite a bit of filtering and protection.

I've had an Uno in a vehicle powered by 12V for a few years with no problems. It's driving some solid state relays (almost no current) and a few LEDs. Of course, your car may have less-stable voltage...

If you include the Zener you should have a fuse. If you you exceed the Zener voltage, it conducts and you can get "unlimited" current through it which can burn-up the Zener and the wiring, etc. That probably won't happen with a short term spike, but if you do kill the Zener it will probably short-out and burn-up the wiring, etc.

The capacitors won't do much either. But if you put a diode between the power source and the capacitors (the capacitors on the Arduino side) they can filter-out negative spikes/voltage drops. The diode keeps the capacitors from discharging back into the car battery and they power the Arduino for a (very) short time until power returns. I'd use at-least 1000uF and I'd leave out the 0.1uF. (I call it a "half-filter" because it only filters-out negative spikes.)

I don't think your filter will do the job you expect.

Questions:

  1. is this a power or signal filter?
  2. will this be connected directly to the automotive power?

The issue is there can be some significant power in the "noise" on an automotive 12V power. It can go up to 16.5Volts for an extended period of time. There are short spikes up to 1600V. Not often but there can be long spikes (100ms) of up to 50V.

So you need some series resistance to absorb the extra voltage. The suggestion to use an automotive rated regulator is good choice, but you still have to filter/clamp the high voltage spikes 1600V. The 1600v spikes are really short and may be absorbed by the wire resistance/inductance.

If your not using much power, put a low value resistor in series with the input. Change the 220µF to 10µf @ 35 or 50V. The 0.01 should be immediately at the input to filter out RF noise.

Another issue you may have is the ground. The ground on an automobile can vary up to 2.5v from one end of the vehicle to the other. So you input signals have to consider that.

Both of these questions where answered in the original post.

Alright onto the circuit in question. This is the main power source for the Arduino. This is a Ignition 'Key On' circuit and will remain powered anytime the key is turned to the on position. This could be a span of seconds to hours, once the key on signal is sent to the arduino, it will execute its program until the key on power is removed.

The alternator was just rebuilt last week and is regulated to 14.8v. I do know that automotive circuits can be noisy and volatile, voltage drops, voltage avalanches, reverse polarity, moisture, humidity, heat, etc.... The ceramic capacitor I am using is automotive grade, EMI suppression safety capacitor and has been tested up to 8kV direct contact ESD.

Application as Y capacitors for EMI suppression and
primary-secondary coupling on battery chargers for
PHEV/EV
• Application as filter capacitors on DC/DC converters for
PHEV/EV and HEV
• EMI / RFI suppression and filtering

In regards to the grounding, my plan is to have a common ground bus from the arduino and all components to the chassis ground. The controller will be mounted in the cab under the dashboard within 24"-36" distance of the battery. Right now I am just trying to get this main power feed sorted. I have changed the layout, added an additional shottky diode and a 21k resistor as that is the biggest I have on hand. This is more about getting the layout and main components correct. I can order bigger or smaller resistors, or capacitors or what ever but right now I have to work with what I have on hand.

I plan on getting this installed in the car possibly as soon as tomorrow and just driving it around and monitoring the voltage output and see if anything releases the magic smoke.

I also just realized that the Arduino Nano Every has a MPM3610 Input Voltage Regulator which seems to make all of this overkill.

The MPM3610 is a high-frequency,
synchronous, rectified, step-down, switch-mode
converter with built-in power MOSFETs,
inductor, and two capacitors. It offers a compact
solution that achieves a 1.2A continuous output
current with excellent load and line regulation
over a 4.5V to 21V input-supply range.

Here is my updated setup I will be testing tomorrow....

Thank you for this input, I changed up my setup to include both a second shottky diode inline on the positive line before the caps. For right now I have to use what I have on hand so I will have to use the 220uF cap, and I moved the 'half-filter' before the 220uF at an other users suggestion.

Also I noted that the Arduino Nano Every includes a MPM3610 Voltage regulator with built in mosfet and DC DC converter with capacitors, so what I am doing is probably overkill?

The AEC-Q200 qualification is the global standard for stress resistance that all passive electronic components must meet if they are intended for use within the automotive industry. Parts are deemed to be AEC-Q200 qualified if they have passed the stringent testing as outlined within the standards. What happen when the road warrior gives you a 24V jump start, this is common and is part of the automotive design. You also know he will eventually hook it backwards for some unlucky person. Then there is Load Dump, very nasty. It can have hundred of amps and lots of voltage, that is another specification. Take a look at AN2689 by ST, Protection of automotive electronics from electrical hazards, guidelines for design and component selection. This should get you started with a good design.

Thank You Gil for your unfortunately unhelpful reply. I am familiar with both the AEC-Q200 qualification and most of the products I am using are in fact AEC-Q200 approved. I have also looked through the AN2689 document, matter of fact which is printed out and sitting within arms reach of me. While it is informative its also a marketing paper for ST Microelectronics products. All of the scenarios listed give a singular solution to that individual scenario but there is no comprehensive overall solution.

More concerning is I was asking for experienced individuals to help me with my design and to see if it was a working solution. I have been an automotive technician, I am familiar with all the perils of the automotive electrical environment as well as the dumb things individuals do with their cars. But what I am not is an electrical engineer, nor do I wish to be one, that is why I am here asking for advice on a solution to a rather simple problem.

This thread pretty much represents while almost every thread on this subject comes to an inconclusive end. Its well meaning folks with no real world practical experience telling other people that they should read some paper or some website which they think contains the answer.
Its not, its not helpful at all.

I am also noticing that people are obviously not reading the actual posts, but just skimming through and piping off with a well meaning but again unfortunately unhelpful reply.

Thank You for your contribution to the thread though, it did at least get me to skim through the ST Micro AN2689 document a 2nd time and at least confirm what I had read previously. Also my apologies if this came across as slightly confrontational but I am looking for specific help, not opinions or references. If you do in fact have a circuit design that you know will solve the issue I would love to see it posted because that in fact would be helpful. Thanks Again.

The 21k resistor is to high for powering an Arduino, also you need a fuse and preferably a 25V version for the 220µF. I have designed electronics for cars and campers so have a bit of experience.
Another challenge will be to clean the input signals, grounding, .........
Will make a schematic and post it soon.

If you really need to clean up the 12 volt power, place an inductance between the two capacitors in you schematic. The value and source of the inductance is up to you. Usually a ferrite core with several turns of wire suitable for your current.

That 21K resistor will certainly limit output current.

And that perfboard deal is a "show stopper", too.

Yes, sir, I found that out via experimentation. Replaced with a 330ohm. I got everything working, even hooked it up to the car. Also found that while the 220uF cap will power a led long after the power is pulled, the Arduino powers off immediately. As others suggested I may need to go yet larger on the cap. But the goal is not to keep it powered after power off, its more about power smoothing.

And Thank You!

I am honestly have not worked with inductors, but will research and possibly incorporate into the final design. Thank You.

Thanks for your input, I replaced the 21k with a 330. Your realize the bread board is strictly for testing purposes :wink:

The output voltage will vary owing to the voltage drop across that resistor, and that depends on the current drawn by the 'protected' circuit.



The 330 ohm resistor is in the wrong place and to high, use something like this:

12V car supply - Schematic.pdf (9,0 KB)

Ok so I see you have replaced the Schottky diode with a zener, and I do have some 20v zener diodes to be able to use. I was under the impression that the Schottky was a better solution as it did not let reverse voltage through. You then have just a standard diode in series on the positive rail, when I tried that with a schottky I did not get any forward voltage curios enough. Finally I see you have what appears to be a very small 10 ohm resistor inline if I am reading that correctly.

I had indeed planned on incorporating a 1 amp fuse in the future. I also like how you tee off the key on input to power the relay coil, smart, I was just thinking about how to simplify the circuits.

In regards to the caps, I don't have any issue resizing. The ceramics I ordered ended up being on the chunky side and would enjoy slimming that down. Same with the the second cap, I don't have a specific reason for the 220uF 16v other then that what was in the original glow plug controller that has lasted from 1985 to 2020 when the vehicle was taken down for restoration.

runaway_pancake,
Thank you for your diagram explaining the voltage drop across the 330 ohm resistor. I appreciate the time you took to make the visual presentation.

Thanks for all the experience and assistance. Its memorial weekend and its time to make some time for some adult beverages and pay a little homage to Tina Turner. Catch ya all on the flip side :wink:

PS: This is just the key on power circuit, I still got the starter signal and alternator high signal to process :grin:

It's a worksheet.

The schematic was intended as a concept, values might change depending on currents and details of the application.
D1 is marked zener but should be a fast one, a TVS type. It will suppress the voltage spikes: Example: SLD15U-017.
D2 is the actual reverse polarity protection and doesn't need to be a fast one.
R1 - C1 - C2 is a filter to clean the 12V. There will be some voltage drop over D2 and R1 but that is no problem. On the contrary: it will lower the supply to the Arduino and make it easier for it's on board voltage regulator.

Voltage regulators are good filters so use 7812 or 7810

Hi,

Check the data sheet on those linear regulators, you need 3V or more on the input compared to the output for them to work.

The difference between input and output is called the drop out voltage.
If the difference is lower the regulator will not function.

Your idea will not work as the input voltage is 12V, you will not get 12V out of a 7812.

Thanks.. Tom.. :grinning: :+1: :coffee: :australia: