Pmod HYGRO Reference Manual
Copyright Digilent, Inc. All rights reserved.
Other product and company names mentioned may be trademarks of their respective owners.
Page 3 of 6
3.2 Temperature and Humidity Registers
The temperature register (address 0x00) and the humidity register (address 0x01) are both 16-bit read only
registers with the 14 MSBs corresponding to the 14-bit maximum resolution for both sensors. The two LSBs (bits
D1 and D0) are always 0 for both registers. As the measurement resolution increases, the corresponding
conversion time for each sensor also increases. A table of typical conversion times from Section 7.5 (Electrical
Characteristics) of the
HDC1080 datasheet
, is provided below.
Relative Humidity Sensor
Temperature sensor
8-bit resolution
2.50 ms
11-bit resolution
3.65 ms
11-bit resolution
3.85 ms
14-bit resolution
6.35 ms
14-bit resolution
6.50 ms
Table 4. Typical conversion times.
Upon device power-up, the Pmod HYGRO requires at least 15 ms prior to being able to perform a measurement.
To perform a measurement, users need to configure (or accept) the measurement settings in the Configuration
Register, and then trigger the measurement(s) by sending an I²C write transaction along with the address pointer
set to the appropriate register. After waiting the
appropriate conversion times listed in Table 4 above, users may
then perform a read transaction, taking advantage of the auto-incrementing pointer address for reading both the
temperature and humidity registers. After the data has been read, users need to wait at least one full second
before performing another read transaction to avoid internal heating of the sensor and the distortion of the
measured temperature and humidity levels.
Note that if a write transaction is performed on either the temperature (address 0x00) or humidity (address 0x01)
registers during a conversion, the current conversion will be aborted and a new one started. If a read is performed
during a conversion, the Pmod HYGRO will respond back with a
NACK
indicating the measurement result is not yet
available. The typical time that it takes the output of the humidity sensor to show 63% of a step change in humidity
is 15 seconds.
3.3 Quick Data Acquisition
Here is the series of commands to acquire relative humidity and temperature data from the Pmod HYGRO in
pseudo I²C code.
1.
Power on the Pmod HYGRO and wait at least 15 ms.
2.
Call the device ID with a write bit
I2CBegin(0x80); //device ID 0x40 with a write (0) bit
3.
Wait to receive an ACK from the Slave Device
4.
Write the device address that you want to talk to
I2CWrite(0x00); //address 0x00 corresponds to the Temperature Register, the
Humidity register will be auto-incremented to next
5.
Wait to receive an ACK from the Slave Device
6.
Delay at least 12.85 ms (6.35 ms for the Temperature Sensor and 6.50 ms for the Humidity Sensor)
7.
Read 4 bytes from the temperature and humidity registers (two 8 byte samples from each, MSB then LSB)