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Old 08-26-2008, 11:19 PM   #11 (permalink)
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Well it worked great all the way home. 3 individual "trips" and no problems.

Got home and tested it with my own multimeter, 5.03 in the car.

Brought it in and plugged it into the computer here with my own cable and it would only run on USB about 10% of the time, the rest of the time it would lock up and go screwy. Voltage was 4.98 sometimes and 4.88 other times here at home. Same erratic flashing light on the board.

One thing I found was that nearly every time I tested the voltage on USB power, it would seem to clear the program, and the screen would do nothing but flash blank. It wouldnt even work in the car. I would have to reflash it to make it work. I tried "verify" and it just repeated back to me the size of the sketch. So I finally reflashed it and didnt measure voltage, and it seems to work ok in the car. Hopefully tomorrow it works better going to work and back.

In the program I did change the default variables to my own, so I wont have to change them every time it clears or resets.

I checked the voltage from 5V to both ground pins and got the same thing. Also tested the voltage at the power jumper pin and it matches that at the 5V pin.

So there is a power "brownout" issue with these boards?

Checking it for hairline cracks is a good idea too, but nearly everything on this board is too small for me to solder. Should have built the kit I guess.

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Old 08-26-2008, 11:37 PM   #12 (permalink)
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Quote:
Originally Posted by wagonman76 View Post
Well it worked great all the way home. 3 individual "trips" and no problems.

Got home and tested it with my own multimeter, 5.03 in the car.

Brought it in and plugged it into the computer here with my own cable and it would only run on USB about 10% of the time, the rest of the time it would lock up and go screwy. Voltage was 4.98 sometimes and 4.88 other times here at home. Same erratic flashing light on the board.
The voltage sounds sufficient. Can you unplug all the mpguino circuitry and see if USB improves? I wonder if the bootloader is corrupted.

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So there is a power "brownout" issue with these boards?
The atmega chip itself is sensitive to erratic power, it can lose the program, or the eprom memory, or the bootloader/fuses if the power hookup isn't solid. You don't want it turning on and off with the ignition.

Going back to the setup screen means the eprom was corrupted, maybe it is overloading the USB power?
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Old 08-27-2008, 12:29 AM   #13 (permalink)
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Thanks dcb. I unplugged all the mpguino circuitry and just ran the board itself. First connected to USB gets me 5.03v. Obviously I dont have a display to check but the light on the board seems to flash properly with the other parts unplugged, unlike any other time lately on USB power. Then I took it out to the car. Same thing there, 5.03v with things unplugged.

The mpguino does not power on and off with ignition. It is soldered to the courtesy circuit, which powers the radio memory and on my car has no way of switching off and is not connected through ignition or ecm or anything else. It is 12v constant power. However, maybe taking it out of the car and plugging it into USB power enough times has taken its toll on it?

If the bootloader is corrupted, how would I go about reflashing that? I did see some things on the arduino site but it is not really clear.
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Old 08-27-2008, 12:47 AM   #14 (permalink)
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Well, if you can reprogram it easily with the mpguino circuitry unplugged, and it works well with it plugged in to the car, then that might be a workaround.

I guess I would plug things in one at a time and see when the usb starts flaking out. Buttons, interface circuit, LCD.

You need an isp cable to load bootloaders, and some patience. I made an isp cable out of an old parallel cable and a few resistors and a bit of hard drive connector. I've revived a couple chips with it and can buy plain atmega168 chips without a bootloader on them. But if your arduino returns to "normal" without the extra circuitry then the extra circuitry is suspect.
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Old 08-27-2008, 02:17 AM   #15 (permalink)
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Thanks dcb, that really helps if I need to do that. Looks similar to an interface cable I made once for my calculator.

I tried things one by one, and it appears that the 2N3906 transistor circuit was making it flake out. Switches and display power connected I got 5.03 volts. Without the transistor connected but display signals connected I got 4.98 volts. With the transistor connected I got 4.87 volts and screwing up after a few minutes (maybe it takes a moment for it to heat up and start leeching power and screwing up). Disconnecting my secondary transistor didnt make a difference, I tried that first.

So what I did was abandon the 2N3906 circuit, and rewire my NPN transistor as the only one. (I posted earlier in the release one workspace thread about what it takes to make this oddball display dim.) I put the control leg to digital pin 9, and break the display ground with the other 2 pins. Forgot what theyre called, but I know it is the correct order. I didnt use a resistor on the control leg.

I ended up with an extremely bright display that still gave me 4.97 volts left over. I knew it would do this, so I took the list of numbers and subtracted them from 255 and reflashed the program, that was the quickest way. The dimming acts normal now. Even with the pwm putting out the full 5v at 255 to dim my display fully, it still gives 4.98 volts left over.

And both in the car AND on the bench so far, it appears to work like a million bucks. I got a feeling I fixed it. Ill let you know tomorrow if I have any more glitches.

Thank you so much for all your help.
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Old 08-27-2008, 09:11 AM   #16 (permalink)
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No Prob, glad you got it under control

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