Hi,
I am experiencing some weird behaviour when certain values get negative. I've reviewed the code many times but I can't find where I'm going wrong.
The project is a temperature and humidity sensor based on the DHT22 sensor (it also still supports the DHT11). It also calculates the dew point from these 2 values. It all works well when all values are positive. Now in winter I have negative values for the first time and the sketch falls over...
The values are requested via serial port using my own "protocol" which consists of two bytes with value 0xCC (indicating the start of a command) then 16bit deviceID, 16bit valueID, 8bit actionID (get, set, reply, event), 8bit statusID (to report back any error as a number) and then two 32bit signed integers containing the actual values (value1 and value2) (most of the time value2 is zero when only one value is needed).
Some of the relevant parts of the code are:
some global variables and defines:
// DHT11/22 sensor variables and pins
#define pin_DHT 12 // DHT11/22 data pin
#define DHTtype 22 // 11 = DHT11, 22 = DHT22
long temp, hum, dew; // current values for temperature, dewpoint and humidity in 1/10th degrees Celsius / 1/10th percent
unsigned long DHTmillis; // timestamp of last sensor read
dht DHT; // DHT sensor object
//Serial comms variables
unsigned int deviceID = 0;
unsigned int valueID = 0;
byte actionID = 0;
byte statusID = 0;
long value1, value2 = 0;
in setup() the temperature and humidity are being read for the first time. Then in loop() it is being updated every 10 seconds (exact same code)
if (DEVICE_TYPE & DEVICE_TYPE_TEMPHUM) // read DHT sensor if this is a TEMPHUM device
{
// check if millis() has rolled over
if (millis() < DHTmillis) DHTmillis = millis();
//read DHT sensor every 10 seconds
if (millis() > (DHTmillis + 10000))
{
if ((DHTtype == 11) || (DHTtype == 22))
{
if (DHTtype == 11) DHT.read11(pin_DHT);
if (DHTtype == 22) DHT.read22(pin_DHT);
temp = (DHT.temperature * (double)10);
hum = (DHT.humidity * (double)10);
dew = (dewPoint(DHT.temperature, DHT.humidity) * (double)10);
}
else
{
temp = -1L;
hum = -1L;
dew = -1L;
}
DHTmillis = millis(); // remember when sensor was read
}
}
Then, when a command comes in to read the temperature, the following function is being called (very similar functions exist for humidity and dew point)
void f_temperature()
{
if (DEVICE_TYPE & DEVICE_TYPE_TEMPHUM)
{
if (actionID == Action_Set)
{
statusID= 106; // Action_Set not supported for temperature
}
else if (actionID == Action_Get)
{
statusID= 0;
value1 = temp;
value2 = 0;
}
actionID = Action_Reply;
serial_send();
}
}
serial_send() looks like this:
void serial_send()
{
byte data[16];
data[0] = 0xCC;
data[1] = 0xCC;
data[2] = id >> 8;
data[3] = (id & 0xFF);
data[4] = valueID >> 8;
data[5] = (valueID & 0xFF);
data[6] = actionID;
data[7] = statusID;
data[8] = value1 >> 24;
data[9] = (value1 & 0x00FF0000L) >> 16;
data[10] = (value1 & 0x0000FF00L) >> 8;
data[11] = (value1 & 0x000000FFL);
data[12] = value2 >> 24;
data[13] = (value2 & 0x00FF0000L) >> 16;
data[14] = (value2 & 0x0000FF00L) >> 8;
data[15] = (value2 & 0x000000FFL);
Serial.write(data, 16);
}
Now, when the value is positive it all works fine and I get a data packet back on the serial port. However, if a value gets negative I get no reply at all. It just does not reply! It does still reply for other values that are positive, so it's not totally unresponsive.
I would be grateful for any hints as to where and why this is going wrong and what to do about it.
