I modified the MPGuino for motorcycle use, and I also added a temperature sensor. Next thing I recognised: format() function doesn't support negative values ^^ Of course, they are not needed in original MPGuino.

If somebody also wants to add meters etc that can return negative numbers, here is my improved one. Beyond support of negatives, I changed:

.) no leading 0 anymore. I don't like the "005.99" Display, so now it shows " 5.99".

.) a second byte parameter gives you control over the amound of post decimal positions. Or, to be more precise, the maxmimum amount you want to be displayed. I don't think it's useful to show the value of a temperatur sensor in "00.00" if it has a precision of +-0.25°C! Also, speed with 2 post decimal positions seems wired to me.

Of course you have to modifiy the screen functions to use this. You also may want to create a format function without "maxdec". As I know, Arduino supports overloading funcions, so that shouldn't be a problem.

Code:

char* format(long num, byte maxdec){ //gets the *1000 value and max post decimal positions
//num = 9125;
fBuff[0] = 0; //start with defined condition
fBuff[1] = 0;
fBuff[2] = 0;
fBuff[3] = 0;
fBuff[4] = 0;
fBuff[5] = 0;
fBuff[6] = 0;
if (num >= 0){ //is num positive?
byte dp = 3;
while(num > 999999){
num /= 10;
dp++;
if( dp == 5 ) break; // We'll lose the top numbers like an odometer
}
if(dp == 5){
dp = 99; // We don't need a decimal point here.
}else{ //see if we have to cut decimals because of maxdec
while(5 - dp > maxdec){
num /= 10;
dp++;
}
if (dp == 5){
dp = 99;
}
}
// Round off the non-printed value.
if((num % 10) > 4)
num += 10;
num /= 10;
byte x = 6;
while(x > 0){
x--;
if(x==dp){ //time to poke in the decimal point?
fBuff[x]='.';
}else if(num == 0 && (fBuff[x+1] < 58 && fBuff[x+1] > 47 || fBuff[x+1] == ' ')){ //have we reached end of number?
fBuff[x]= ' ';
}else{
fBuff[x]= '0' + (num % 10);//poke the ascii character for the digit.
num /= 10;
}
}
}else{ //num is negative!
byte dp = 4; //we loose the last digit because leading "-"
num /= 10; //shift to dp=4
boolean minussign = false;
while(num < -99999){
num /= 10;
dp++;
if( dp == 5 ) break; // We'll lose the top numbers like an odometer
}
if(dp == 5){
dp = 99; // We don't need a decimal point here.
}else{ //see if we have to cut decimals because of maxdec
while(5 - dp > maxdec){
num /= 10;
dp++;
}
if (dp == 5){
dp = 99;
}
}
// Round off the non-printed value.
if((num % 10) < -4) //% returnes - values!!
num -= 10;
num /= 10;
byte x = 6;
while(x > 1){
x--;
if(x==dp){ //time to poke in the decimal point?
fBuff[x]='.';
}else if (num == 0 && fBuff[x+1] != '.'){ //have we reached end of number?
if (minussign == false){
fBuff[x]= '-';
minussign = true;
}else{
fBuff[x]= ' ';
}
}else{
fBuff[x]= '0' - (num % 10);//poke the ascii character for the digit.
num /= 10;
}
}
if (minussign == false){ //no sign until yet?
fBuff[0]= '-';
}
}
//fBuff[6] = 0; //end string identifier
return fBuff;
}

PS: Yes, maybe it could be shorter. But it works

Edit: little code change, there was a bug in it. Someone knows why fBuff has to be initialised as a global variable? I tried to define it in format(), and it messed up the display.