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Old 04-05-2008, 08:36 PM   #1 (permalink)
dcb
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Turtle opengauge development: gunio technical considerations

The stand alone opengauge (aka MPGGuino, or guino for short), has a number of issues to consider:

Display:
1. [deleted my 8 bit ramblings, suggest using the 4 bit library that is being worked on:] http://www.arduino.cc/playground/Code/LCD4BitLibrary

2. Display Size.
Displays in general, the more the better. 20x4 would be my vote (or 1024x768), but I am only starting to understand the technical limitations facing a bigger display. But it should be at least as big as the arduino so we can hide the arduino behind it.

3. Display Interface.
[deleted interface stuff, 4 bit libraries look sufficient, moved flow to organization]

Development Environment
I like the ease of the arduino ide, and how it can drop down to AVR with relative of ease. I also like that there are a lot of people using it and posting solutions to real world problem. I also like the fact that it is free, and open source (so you can look and see how millis() is implemented) and the free version is not deliberately crippled.


Persistence:
The atmega specs list the 512 byte EEPROM memoy (where we will keep the trip data that persists when the atmega is turned off) as only allowing 1000000 writes, then apparently it turns to dust. This means we do NOT want to save the persistent trips once a second!!! One logical solution would be to save them when the key is turned off, but we will need a digital pin tied to ignition power to do that.

Trip Organization:
With only 512 bytes of persistent data storage, we need to think somewhat carefully about what we save from run to run. If we have a persistent tank trip and a handful of other trips, they should each take about 20 bytes, assuming a similiar structure as below, which means about 26 persistent trips maximum, that get updated when the ignition is switched off.

//things will start rolling over @ about 1900 hours
class Trip{
unsigned long seconds;
unsigned long injHi;
unsigned long injHiOverflow;//need more precision on the injectorHI time
unsigned long injCount;
unsigned long vssCount;
}

in the one second loop()...
make a copy of the instant trip and reset it
clear lcd
if(english)
print("MPG<TAB/>MPH<TAB/>MLS<TAB/>HRS");
else
print(something besides english);
go to next lcd line
for(int trip = 0; trip < NumLines; trip ++){
trips[trip].printData();
go to next lcd line
}

in Trip.printData(){ //functions handle conversions to english/metric
printConsumption();
printVelocity();
printDistance();
printTime();
}

add setup options to hide the header row, and to keep the instant trip row always viewable.

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Last edited by dcb; 04-06-2008 at 12:18 PM.. Reason: wrong url, the first one doesn't compile yet
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