what is double ?
The value to be converted.
what is signed char ?
The width of the string to be produced. Why an signed char? Beats me.
what is unsigned char ?
The precision - the number of places after the decimal point. Why an unsigned char? Beats me.
what is char* ?
The buffer where the string is to be created.
float someTemp = 14.5;
char buffer[10];
dtostrf(someTemp, 8, 3, buffer);