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Old 03-25-2009, 12:17 PM   #1 (permalink)
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Unhappy Fried my Guino

I was sitting at the gas station refilling my tank this morning and I went to remove my Guino from the dashboard to get it's current tank data so I can compare it to the pump and odo.

This probably wouldn't have been an issue if I had just put the buttons, or access to thereof, on the outside of the enclosure. Since I didn't I have to remove it from it's velcro'd location in front of the tachometer, open the front of the box, and hit the buttons from there. Usually it's fine except for the odd power cycle due to nudging the cable here and there.

When I touched the box, I got a static shock that actually registered on the display (the instant MPG went to 9999 from 0000 so I'm guessing it thought it was a VSS pulse). I was a bit nervous after that, but since it returned to normal I figured it was ok.

Now when I grabbed the box to pull it off the case closed suddenly, as if it wasn't closed completely to begin with, with a snap that put the display in an odd position (all the way through the hole, when it's normally angled slightly) and messed up the screen quite a bit. The left half was ok but the right half faded from barely visible to not visible. I was a little freaked out, but hit the buttons to make sure it wasn't completely gone. The screens changed and it reset the current and tank but then I saw smoke coming from between the boards, the screen went blank, and I smelled burning electronics. I removed the phone cable after that and hopefully I just fried the screen.

Not good. I'll have to dismantle it at home tonight to see if I can find where it burnt and for now I have no instant feedback. Maybe I can fix it, maybe I'll end up holding out for the OBDuino. *sigh* That'll teach me to not finish my projects before using them.

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Old 03-25-2009, 12:42 PM   #2 (permalink)
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My sympathies! Hope you get back to instant feedback soon.

Static is a common phenomenon in cars, and I wonder how it would be possible to reasonably shield / harden the MPGuino against such instances. Maybe it needs some collaboration and chasing.

I am also worried about the raw 12V from the battery - There is nothing for surge protection on the MPGuino, whereas I routinely come across specialized surge resistant linear/switch mode regulators being advertized for automotive use. At least some sort of surge protection diodes should be used on all inputs and power lines.

Any comments?
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Old 03-25-2009, 12:47 PM   #3 (permalink)
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I've scoped the 5v output while playing with various inductive loads, the large and small caps and the 7805 seem to do a good job.
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Old 04-02-2009, 04:52 PM   #4 (permalink)
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Yup, I fried the screen. One of the big black dots on the back was burnt. Of course the solder sucker and desoldering braid did absolutely nothing helpful to remove the solder so now I need a new bridge piece to go along with the new screen. The main board is a bit chewed up as well so hopefully I didn't ruin it.... I'll have to test it...

Anyone have part numbers for ordering the screen and bridge outside of the kit?
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Old 04-05-2009, 07:24 PM   #5 (permalink)
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This type of situation brings up the question of circuit protection. Considering how easy it can be to fry the MPGuino, how easy would it be to damage the cars control system at the same time?

What I want to know is if there is a way to add circuit protection to the unit? Possibly optoisolators and fuses. Has anyone else tried this? Would the optoisolaters cause problems with signal delay or loss? I have looked at these units for a while but this is a situation that I have always worried about. I would personally isolate both the data lines and would install a fast acting fuse on the power line. Anyone else tried this? Could the car get damaged by sending 5v or grounding any of the lines?
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Old 04-05-2009, 08:14 PM   #6 (permalink)
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I don't know that "easy to fry" is a fair generalization. In a home built unit, stuff happens, yes, but adding more stuff generally reduces the chances of success. It sounds like a layer of plastic between his board and LCD would have helped here.


The preassembled ones currently come with a layer of plastic between the LCD and the circuit board. They also do not have a bootloader and other changes and have not yet shown the flash flakiness seen in a stock arduino configuration. The data leads have 50kohms in series so it's hard to fry much of anything with that in the way. And a large cap with reverse polarity protection on the power leads make a reasonable supply circuit.
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Old 04-05-2009, 08:22 PM   #7 (permalink)
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Quote:
Originally Posted by dcb View Post
I don't know that "easy to fry" is a fair generalization. In a home built unit, stuff happens, yes, but adding more stuff generally reduces the chances of success. It sounds like a layer of plastic between his board and LCD would have helped here.


The preassembled ones currently come with a layer of plastic between the LCD and the circuit board. They also do not have a bootloader and other changes and have not yet shown the flash flakiness seen in a stock arduino configuration. The data leads have 50kohms in series so it's hard to fry much of anything with that in the way. And a large cap with reverse polarity protection on the power leads make a reasonable supply circuit.
The idea that I was presenting is that bad things happen and while frying the MPGuino is not that bad, what happens if something shorts out and shorts the wires going to the ECM? Would that damage it? The idea that I have is to use opto-isolators to isolate the ECM from all home build projects so that if something did happen, you would at most have some fried opto-isolators but the car would still be fine. One thing I could see happening is the possibility of introducing interference by tapping into the cars system. Therefore, it would make sense to keep our interaction with the system purely one sided which would give us the piece at mind that nothing could happen to our cars if something went wrong with our project. Therefore, what I really wanted to know is has anyone tried to isolate the project from their cars systems?
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Old 04-06-2009, 12:09 PM   #8 (permalink)
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An opto-isolator would probably introduce more interference on the signal lines. You have to supply enough current to light an LED with an opto-isolator, as compared to triggering a high impedance input pin.

As for the other general "stuff happens" concern, I don't know that one can prevent the occasional miswiring in a cost effective manner. Even "professional electronics installers" occasionally miswire something or short something out. But if the thought of hooking up 4 wires causes you unusual distress then you should look into an obd based solution. What kind of car do you drive?

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Old 04-06-2009, 02:37 PM   #9 (permalink)
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Quote:
Originally Posted by dcb View Post
An opto-isolator would probably introduce more interference on the signal lines. You have to supply enough current to light an LED with an opto-isolator, as compared to triggering a high impedance input pin.

As for the other general "stuff happens" concern, I don't know that one can prevent the occasional miswiring in a cost effective manner. Even "professional electronics installers" occasionally miswire something or short something out. But if the thought of hooking up 4 wires causes you unusual distress then you should look into an obd based solution. What kind of car do you drive?

P.S.
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Thanks for the welcome.

Dont get me wrong here, I love working on wiring which is why I am becoming an electrical engineer. I just like to think about the ill-effects a project could cause before I do work...sometimes...at least when it comes to something as expensive as a car. Personally, I believe all cars should have some sort connection for modders to safely tap into the cars systems but unfortunately its not that easy.

As for my car, I drive both a 2002 Chevy Z71 Suburban and a 1987 300TD Mercedes. Both cars are unique for the work ive done on them. The Suburban could be considered the electrically modded car. I have done the basics such as replacing the entire radio system with a much higher quality system capable of dual zone sound, I have installed flood lights under the rear for backing up in the dark, and I ran a 100 amp electrical connection from the battery to a fuse block under the cup holder for my inverter and for future projects. I have even pulled apart most of the dash board electrical system just to see how it worked. While this car is not the most fuel efficient car out there, we only really use it when we need to haul large loads or go on road trips.

The other car, the Mercedes, is my main focus of installing a MPGuino. The background of this car is interesting. First off, its been converted to run on Bio-Diesel, Vegetable Oil, or whatever else we want to put in it. The reason for this is that my Dad runs a bio-fuel research program at my old high school on the weekends. We are researching different fuel blends and their emissions. Currently, we have been using a set test route to measure our distance and we have been getting our MPG by weighing a test tank we have in the trunk. While this method is great for overall MPG, its not practical for instantaneous MPG. I have the wiring diagrams for the car as well but I did hear a mention that Diesel cars have a slightly separate signaling method which worries me. Anyway, I should probably start a separate thread if I want help on that, I really dont want to derail this topic any more than it is.
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Old 04-06-2009, 05:43 PM   #10 (permalink)
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For your mercedes, I would suggest taking a look at some of the mpguino diesel threads, you will be in for some pretty serious experimentation at least:

http://ecomodder.com/forum/showthrea...tion-6778.html

Or the "carbureted mpg monitor" thread might give you some ideas as well.

http://ecomodder.com/forum/showthrea...gine-1123.html

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