Hi All,
I am wanting to use the temperature registers on a DS3231 as a local temperature indicator. I can read and set all of the time registers at will. But the temperature registers have nonsense values.
Here is a sample of the output of the program below:
Sun, 9/8/15 - 1:28:25
temperature bytes: 154 130
Sun, 9/8/15 - 1:28:26
temperature bytes: 154 130
Sun, 9/8/15 - 1:28:27
temperature bytes: 154 130
Sun, 9/8/15 - 1:28:28
temperature bytes: 154 130
Sun, 9/8/15 - 1:28:29
temperature bytes: 154 130
Sun, 9/8/15 - 1:28:30
temperature bytes: 154 130
Sun, 9/8/15 - 1:28:31
temperature bytes: 154 130
Sun, 9/8/15 - 1:28:32
temperature bytes: 154 130
Sun, 9/8/15 - 1:28:33
temperature bytes: 154 130
Sun, 9/8/15 - 1:28:34
temperature bytes: 154 130
Sun, 9/8/15 - 1:28:35
temperature bytes: 154 130
Sun, 9/8/15 - 1:28:36
temperature bytes: 154 130
Sun, 9/8/15 - 1:28:37
temperature bytes: 154 130
Sun, 9/8/15 - 1:28:38
temperature bytes: 154 130
Sun, 9/8/15 - 1:28:39
temperature bytes: 154 130
Sun, 9/8/15 - 1:28:40
temperature bytes: 154 130
Sun, 9/8/15 - 1:28:41
temperature bytes: 154 130
Sun, 9/8/15 - 1:28:42
temperature bytes: 154 130
Sun, 9/8/15 - 1:28:43
temperature bytes: 154 130
As can be seen the time increments nicely. All that part works.
However the MSB of the temperature is 154, which is a negative number as the sign bit is set according to the data sheet (8 bit 2's complement). Ignoring the LSB fractional part for the moment that makes it -102 Celsius in here and while it isn't as warm as it might be, it isn't under zero. This reading is nonsense.
DS3231 is keeping perfect time - so I suspect it is what I am doing. But it looks OK to me. Is there something tricky about the data in the registers the datasheet does not indicate.
Any ideas?
Here is the code I am using: (Thanks to Arduino basics - Real Time Clock RTC DS3231) slightly modified as I didn't like the conversion to float used but before that I need good data.
#include <Wire.h>
#define DS3231_I2C_ADDRESS 104
// SCL - pin A5
// SDA - pin A4
// To set the clock, run the sketch and use the serial monitor.
// Enter T1124154091014; the code will read this and set the clock. See the code for full details.
//
byte seconds, minutes, hours, day, date, month, year;
char weekDay[4];
byte tMSB, tLSB; // temperature bytes here
float temp3231; // not used
void setup()
{
Wire.begin();
Serial.begin(9600);
}
void loop()
{
// watchConsole(); // don't need this DS3231 already set and battery backed
get3231Date();
Serial.print(weekDay); Serial.print(", "); Serial.print(date, DEC); Serial.print("/"); Serial.print(month, DEC); Serial.print("/"); Serial.print(year, DEC); Serial.print(" - ");
Serial.print(hours, DEC); Serial.print(":"); Serial.print(minutes, DEC); Serial.print(":"); Serial.println(seconds, DEC);
get3231Temp();
delay(1000);
}
// Convert normal decimal numbers to binary coded decimal
byte decToBcd(byte val)
{
return ( (val/10*16) + (val%10) );
}
void watchConsole()
{
if (Serial.available()) { // Look for char in serial queue and process if found
if (Serial.read() == 84) { //If command = "T" Set Date
set3231Date();
get3231Date();
Serial.println(" ");
}
}
}
void set3231Date()
{
//T(sec)(min)(hour)(dayOfWeek)(dayOfMonth)(month)(year)
//T(00-59)(00-59)(00-23)(1-7)(01-31)(01-12)(00-99)
//Example: 02-Feb-09 @ 19:57:11 for the 3rd day of the week -> T1157193020209
// T1124154091014
seconds = (byte) ((Serial.read() - 48) * 10 + (Serial.read() - 48)); // Use of (byte) type casting and ascii math to achieve result.
minutes = (byte) ((Serial.read() - 48) *10 + (Serial.read() - 48));
hours = (byte) ((Serial.read() - 48) *10 + (Serial.read() - 48));
day = (byte) (Serial.read() - 48);
date = (byte) ((Serial.read() - 48) *10 + (Serial.read() - 48));
month = (byte) ((Serial.read() - 48) *10 + (Serial.read() - 48));
year = (byte) ((Serial.read() - 48) *10 + (Serial.read() - 48));
Wire.beginTransmission(DS3231_I2C_ADDRESS);
Wire.write(0x00);
Wire.write(decToBcd(seconds));
Wire.write(decToBcd(minutes));
Wire.write(decToBcd(hours));
Wire.write(decToBcd(day));
Wire.write(decToBcd(date));
Wire.write(decToBcd(month));
Wire.write(decToBcd(year));
Wire.endTransmission();
}
void get3231Date()
{
// send request to receive data starting at register 0
Wire.beginTransmission(DS3231_I2C_ADDRESS); // 104 is DS3231 device address
Wire.write(0x00); // start at register 0
Wire.endTransmission();
Wire.requestFrom(DS3231_I2C_ADDRESS, 7); // request seven bytes
if(Wire.available()) {
seconds = Wire.read(); // get seconds
minutes = Wire.read(); // get minutes
hours = Wire.read(); // get hours
day = Wire.read();
date = Wire.read();
month = Wire.read(); //temp month
year = Wire.read();
seconds = (((seconds & B11110000)>>4)*10 + (seconds & B00001111)); // convert BCD to decimal
minutes = (((minutes & B11110000)>>4)*10 + (minutes & B00001111)); // convert BCD to decimal
hours = (((hours & B00110000)>>4)*10 + (hours & B00001111)); // convert BCD to decimal (assume 24 hour mode)
day = (day & B00000111); // 1-7
date = (((date & B00110000)>>4)*10 + (date & B00001111)); // 1-31
month = (((month & B00010000)>>4)*10 + (month & B00001111)); //msb7 is century overflow
year = (((year & B11110000)>>4)*10 + (year & B00001111));
}
else {
//oh noes, no data!
}
switch (day) {
case 1:
strcpy(weekDay, "Sun");
break;
case 2:
strcpy(weekDay, "Mon");
break;
case 3:
strcpy(weekDay, "Tue");
break;
case 4:
strcpy(weekDay, "Wed");
break;
case 5:
strcpy(weekDay, "Thu");
break;
case 6:
strcpy(weekDay, "Fri");
break;
case 7:
strcpy(weekDay, "Sat");
break;
}
}
void get3231Temp()
{
//temp registers (11h-12h) get updated automatically every 64s
Wire.beginTransmission(DS3231_I2C_ADDRESS);
Wire.write(0x11);
Wire.endTransmission();
Wire.requestFrom(DS3231_I2C_ADDRESS, 2);
if(Wire.available()) {
tMSB = Wire.read(); //2's complement int portion
tLSB = Wire.read(); //fraction portion
Serial.print("temperature bytes: "); Serial.print(tMSB); Serial.print(" "); Serial.println(tLSB);
}
else {
//oh noes, no data!
}
return;
}
