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So I request actual proof behind the statements requesting a change
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I want to be very clear, I do not (and certainly and obviously have no right or power to ) ask for a change. I am only providing a warning of *possible* pitfalls. The final circuit is your decison.
I do agree with simplicity, and support you staying with a 2 line display, especially since that is what I bought.
All my duino parts are sitting on my workbench and I have not assembled it yet.
My comments are based on making circuits for my cars in the past.
My *experience* with every circuit *I* have made to control something for a car (a windshield wiper delay, and a trailer light controller to go from the automotive 3 fillament circuit to the trailer 2 fillament circuit) using cmos logic is that it dies
months later *unless* it is strictly isolated from/protected from the car, both the inputs and the outputs, (I use relays to isolate outputs, and optos to isolate inputs).
In addition, I have found thru bitter experience that my power supply must have an input choke and a range of capacitor sizes to trap the different harmonics of spikes and hash and trash that the automotive electrical supply is full of. I have looked at the automotive 12 V supply with my scope ( Tektronix 475 ) before and along with random noise, there are very narrow spikes whenever something inductive (motors, door locks) in the car switches off, and happens every few seconds on the car I tested.
Beyond that, I now use twisted pair wire for every connection, to avoid picking up all the radiated electrical noise, and I do not share share my power ground connection with my "input signal from the car" ground connection on my circuit boards, instead I route that back thru the twisted pair to the car body directly.
You are correct that I have no proof that your system will not work. I doubt it is possible to *prove* that. What would I do to prove it, put 100 duinos with zeners in 100 different models of cars as a field trial and see how many have died after a year? I have never tried zeners for circuit protection. I do know that special schottky diodes are used in circuits that must deal with very fast risetimes, like in switching power supplies. All I have to go on is my history of having circuits die
after a few months, and having to re-make them. That has made me very, very cautious, perhaps overly so.
Being ship-a-product minded, I know my bosses boss (plant manager) will not be down in engineering yelling if I put in more parts, a bigger fan, a duct, a bigger heatsink. He has no idea what we put in, his degree is in accounting, he only *insists* on choosing the color of the paint on the cabinet and the heads of visible screws. Usually he is busy playing golf while giving passing out "perks" in white envelopes to the distributers he plays golf with. He WILL be yelling if the product starts having failures in the field and we get returns from distributors. THAT will interrupt playing golf.