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Old 03-20-2010, 08:58 PM   #161 (permalink)
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Thats a reasonable approach.

They ship with a 50k in series and a 50k pulldown, so I think if you put a 5k (4.7k should work too) in parallel with the existing series resistor (easier than removing and replacing it) you will be left with the equivalent of 4545 ohm resistor in series. And the voltage drop across the series resistor should be less than half a volt leaving 4.5 volts which is plenty.

It is the rightmost blueish colored resistor in this pic

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Old 03-20-2010, 09:10 PM   #162 (permalink)
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resistor mod

Thank you gents. Once I get through with class I'll try it out.

[edit] I finally got my homework done, and soldered a 4.7kohm resistor in. This is the same resistor value I used to modify my IAT sensor wire. In that case, it tricks the PCM into thinking it is 20* cooler outside. Good for hotter temps in the summer. Here is a picture of my solder job...
I had to cobble my picture together w/MS paint so I could shrink it.
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Old 03-21-2010, 12:32 AM   #163 (permalink)
Grrr :-)
 
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Hmm This thing uses your speed to calculate mileage? what if your speed is NOT accurate? can I adjust the guino to take this into account? for example to get proper mpg readings I have to multiply my trip odo output by 1.05

Can I program such a correction into the guino? can I maybe adjust it so it shows my "actual" speed and not reported speed since the reported speed is incorrect ?
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Old 03-21-2010, 01:44 AM   #164 (permalink)
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Technically speaking, it uses distance to calculate mileage. The so-called vehicle speed sensor in a vehicle really generates "X" pulses per mile, regardless of the vehicles speed. The mpguino simply counts pulses for distance, and computes pulses/time to display mph.

All we are doing here is go from a 12 volt vss signal to a 5 volt signal though.

You can of course adjust the speed/distance and the fuel, and a few other tweaks, with the menus. Here is the calibration procedure: Mpguino calibration - EcoModder
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Old 03-21-2010, 02:27 AM   #165 (permalink)
Grrr :-)
 
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well yes I should have said speedometer :-) that does present some interesting potentials such as installing multiple mpguino's to replace my trip and speed readouts as well as mpg readout.

it would be so awesome if we could output this guino data to a PDA or something in real time (ir or bluetooth etc..) so we could make a "glass" or "digital" dash type system for our cars. a couple of tungsten e's or a nokia tablet would work quite nicely with the right gui :-)

also what about reading the "fuel" sender unit data to get a more accurate fuel gauge? Temperature? is anyone working on things like this? hell on my van there is enough space to install a tablet computer as a replacement for the dash board. Just need software for the gui a way to READ the data and a way to make the 2 talk "fast" enough to approximate real time etc..

also is there a way to "store" data each time the car is turned off into non volatile memory so if you lose power you don't lose long term data?

also can this "log" data? RTC for date stamping?

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Old 03-21-2010, 10:26 AM   #166 (permalink)
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The mpguino accumulates data every 1/2 second and spits it out the UART port pin @9600 baud. From there it is a couple bucks to connect to a serial port or ~$20 to connect to a usb port (FTDI adapter). RTC could be computed by the log analyzer program given the start of the log.

It does save the setup data to eprom. Some folks have tweaked the source to save the tank values also, but it is typically a developer who removes it a lot. Mine stay plugged in pretty much permanently, and there hasn't been enough room in the chip to do anything fancy anyhow.

The fuel sender is horribly inaccurate, not worth messing with IMHO.
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Old 03-23-2010, 12:04 AM   #167 (permalink)
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Quote:
Originally Posted by dcb View Post
Thats a reasonable approach.

They ship with a 50k in series and a 50k pulldown, so I think if you put a 5k (4.7k should work too) in parallel with the existing series resistor (easier than removing and replacing it) you will be left with the equivalent of 4545 ohm resistor in series. And the voltage drop across the series resistor should be less than half a volt leaving 4.5 volts which is plenty.

It is the rightmost blueish colored resistor in this pic
Well, that did not do the trick. I drove the truck today and it is peculiar. I only get a reading below 10 mph. It also seems to get faster as I slow down? Maybe I need to go back to the second wire I soldered into. I was also looking at trying to put together a voltage doubler: http://www.national.com/ds/LM/LM2586.pdf#page=22
This thing supposedly takes 5v and ramps it up to 12v.
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Old 03-23-2010, 07:49 AM   #168 (permalink)
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Dont double the voltage. My honda's vss is 5v (actual 4.7v), and it works fine with the smaller resistor, but i did have problems with the original 100k. What i did was measure vss voltage on both sides of the resistor, and found that the level was dropping too low, to around 2.5v. When i jacked up the car & spun the wheel, i got better pulses at slow speeds, and was losing pulses when i spun it fast.

What voltage levels does yours have? They should bounce from 0 to over 3v as the wheel turns.

When you say it gets faster as you slow down, what numbers are you getting?
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Old 03-24-2010, 05:07 AM   #169 (permalink)
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I have not tried measuring the voltage like that. I might have to jack the whole rear end since I have a locker. My system is supposed to be 5v for the vss.
I thought I was using the wrong wire, so I changed to the vss input wire, but I only see figures for speed below 5-10 mph, depending upon if I am just taking off or slowing down. It will be up pretty high, say 30 or so, then drop gradually to nothing by the time I hit 5-10 mph on the speedo.
However, I probably won't get to it until Saturday due to my work schedule...I'll go back to the vss output, then see if I can read the voltage when I spin the wheels.
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Old 03-24-2010, 05:43 PM   #170 (permalink)
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Nickdigger, now I realize I should have asked how you measured the voltage and where before I tried it myself. I cooked my gizmo today. It doesn't power up.
Anyhow, I jacked up the rear end of the truck so the wheels would spin. I then tried to measure voltage from the VSS wire to the negative 12v wire while spinning a wheel, and got nothing. I tried using vdc and adc. I then cranked up the truck and tried it putting it in drive. Nothing? Then I wondered if I needed connect the MPGuino and check it, so I connected it and tried the same leads. Not sure 'cuz I had the MPGuino display down while I was watching my meter. Then I tried across the 12v pos and vss, my meter went negative, and I think that's when I cooked the MPGuino. Very disappointing. Do you think I fried the chip? I cannot see or smell anything burnt. Sigh.

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