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-   -   Swap out the 4004? (

wyatt 09-27-2010 05:54 PM

Swap out the 4004?
Over the weekend I installed a prebuilt (DCB version via another forum member) MPGuino in my car, but couldn't get it to run. The screen wouldn't light up, so I started checking for known voltages (I had built one before). I checked for voltage at the plug, +12VDC (WHEW), I checked all the pins on the screen, all 0VDC, so I figured that power was broken somewhere, and I may be able to bypass/replace parts as needed. I checked power coming into the 4004, +12VDC, and coming out, 0VDC. So I am wondering if the 4004 is dead, and if I should replace it. If so, I plan on cutting it out and soldering a new one in. It is even possible that I have one in my baggy of electronic gadgets I have amassed since I built my first MPGuino, so it **could** be an easy fix (if it turns out that this is the only problem). Suggestions? Thanks in advance!

dcb 09-27-2010 06:34 PM

if it fried open you can loop another diode in parallel. But you might double check the polarity of your connections first.

wyatt 09-28-2010 11:13 AM

Hmmm... Polarity.... I will check that when I get home, then see if I have a spare 4004...

dcb 09-28-2010 04:36 PM

If you send it to amy with a sase we can take a look at it. I've got plenty of 4004s

wyatt 09-30-2010 12:29 PM

I think the wires are hooked up wrong... I made a grave mistake of buying a couple second hand phone jacks to make the hookups easier. I assumed RED = 12VDC, BLACK = GROUND, YELLOW = INJ, GREEN = VSS. I just screwed the wires in, done. I think it has come back to bite me. It looks like the order of black, red, green, yellow is not the same on both jacks. I am going to pull it apart this weekend and really look at it, but it appears as though the problem more than likely is not component related...

dcb 09-30-2010 01:05 PM

please ignore the random color assignments and refer to this diagram :)

wyatt 10-05-2010 05:38 PM

I figured out which line was the +12V, and which was the ground, and just hooked the other two up. IT WORKS! Well, the LCD lights up and it gives measurements. At first I had the INJ and VSS backwards, so I swapped them around. Now, the INJ seems to be working correctly, giving around .2 gallons per hour at idle (warmed up), but the VSS has something screwy. It reads around 15mph when parked with the engine on, and will go up if I rev the engine... The MPGuino also will not go to sleep. Is it possible that the VSS and INJ lines are touching? I haven't been able to locate anything that is off nominal... Also, this may be unrelated (or standard), but the LCD seems to flicker, having waves running down it. Is is possible I still have wires hooked up incorrectly?

wyatt 10-11-2010 12:08 PM

I figured things out...

I had run the wires into a phone jack, then a phone wire to another phone-jack-hookup, that goes to the MPGuino...
I had made good connections to the first phone jack, so I never went back and checked it (plus it was a pain in the butt to get to). I pulled it out this weekend, opened it up, and the VSS wire came shooting out... my "good connection" apparently not so good... I stripped more wire off them and did a good hookup this time, for real (hopefully). I then double checked the wires at the MPGuino, making sure the correct ones went to the correct pins (jacked the car and turned the wheel). I tried it out this morning, and everything seems to be working.
I don't think the flicker on the LCD is a problem, I think it may just be the way the LCD's look.
The MPGuino still won't go to sleep (I have changed it's setting to 3 minutes). Is it possible to just wire in a switch (remove the existing power pin) and turn off the MPGuino's display when I arrive at my destination? I know it will work, I guess my real question is, how much energy does it use turned on (but not running the display) vs. in sleep mode? I know it doesn't take much to run it as it is, but I would hate to have the car not start when I need it...

dcb 10-11-2010 01:14 PM

what hardware version is it? if it is 1.3 you can possibly modify it to use ignition power for the backlight only (or tie it into the dashboard dimmer circuit). I don't know why it isn't going to sleep, what are the gph and mph readings when you stop the car? it is still getting some sort of signal is all I can think of.

wyatt 10-11-2010 02:20 PM

So what I think I am hearing is:
The main board doesn't consume much power, even when on. Thus, a switch, or switched power (which I already have tapped into) would be viable options to keep the main board from losing data.
I am running v.0.80. I can swap the chip with the one from my old MPGuino (maybe v.0.72?) or one of the new 328 chips I have. I was reading 000.00gph and 000.00mph when parked this morning... but that gives me another idea... maybe switch off (or to test, just remove) the VSS and INJ and see what happens...
How do I reset current and tank MPG figures? If I just switch the LCD I won't lose the current MPG figure, but can reset it when arriving or before leaving.
Thanks DCB!

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