io uso questa funzione per convertire da float to string...credo sia il caso tuo...in sostanza vuoi inviare un numero variabile magari di un sensore...
prima di void setup inserisci questa riga:
//Function converts float to char array to display on LCD
char * floatToString(char * outstr, float value, int places, int minwidth, bool rightjustify);
questa riga dopo il void loop(void):
char buff[5]; //buffer per funzione floatToString
per scrivere sul display dovrai fare:
Serial.print(floatToString(buff,temp,1,0,false));
prendi tutto con le pinze xo' a me funziona 
la variabile visualizzata e' temp, il valore dopo temp e' quanti numeri vuoi dopo la virgola, gli altri cosi' su 2 piedi non ricordo.
poi se qualcuno ha idee migliori o funzioni piu' snelle e veloci che ben venga, io sono allo stato primordiale in questo mondo.
// floatToString.h
//
// Tim Hirzel
// tim@growdown.com
// March 2008
// float to string
//
char * floatToString(char * outstr, float value, int places, int minwidth, bool rightjustify) {
// this is used to write a float value to string, outstr. oustr is also the return value.
int digit;
float tens = 0.1;
int tenscount = 0;
int i;
float tempfloat = value;
int c = 0;
int charcount = 1;
int extra = 0;
// make sure we round properly. this could use pow from <math.h>, but doesn't seem worth the import
// if this rounding step isn't here, the value 54.321 prints as 54.3209
// calculate rounding term d: 0.5/pow(10,places)
float d = 0.5;
if (value < 0)
d *= -1.0;
// divide by ten for each decimal place
for (i = 0; i < places; i++)
d/= 10.0;
// this small addition, combined with truncation will round our values properly
tempfloat += d;
// first get value tens to be the large power of ten less than value
if (value < 0)
tempfloat *= -1.0;
while ((tens * 10.0) <= tempfloat) {
tens *= 10.0;
tenscount += 1;
}
if (tenscount > 0)
charcount += tenscount;
else
charcount += 1;
if (value < 0)
charcount += 1;
charcount += 1 + places;
minwidth += 1; // both count the null final character
if (minwidth > charcount){
extra = minwidth - charcount;
charcount = minwidth;
}
if (extra > 0 and rightjustify) {
for (int i = 0; i< extra; i++) {
outstr[c++] = ' ';
}
}
// write out the negative if needed
if (value < 0)
outstr[c++] = '-';
if (tenscount == 0)
outstr[c++] = '0';
for (i=0; i< tenscount; i++) {
digit = (int) (tempfloat/tens);
itoa(digit, &outstr[c++], 10);
tempfloat = tempfloat - ((float)digit * tens);
tens /= 10.0;
}
// if no places after decimal, stop now and return
// otherwise, write the point and continue on
if (places > 0)
outstr[c++] = '.';
// now write out each decimal place by shifting digits one by one into the ones place and writing the truncated value
for (i = 0; i < places; i++) {
tempfloat *= 10.0;
digit = (int) tempfloat;
itoa(digit, &outstr[c++], 10);
// once written, subtract off that digit
tempfloat = tempfloat - (float) digit;
}
if (extra > 0 and not rightjustify) {
for (int i = 0; i< extra; i++) {
outstr[c++] = ' ';
}
}
outstr[c++] = '\0';
return outstr;
}