The purpose of this project was two-fold: to try a new for me ultra low-power RL78 microcontroller manufactured by Renesas and a new digital temperature and humidity sensor HIH-6130 from Honeywell. The average power consumption of this device is about 1.3 μA. So, it should run for more than 10 years non-stop from a CR2032 battery. The device only displays only positive temperatures in °C. Temperature and humidity values alternate on display with about 4 sec period.
| Measuring temperature | Measuring humidity | |
The schematic is pretty simple: microcontroller drives LCD by using a software driver and communicates with sensor via the I2C interface on 80 KHz frequency. In active mode the μC is clocked at 8 MHz from the internal high-speed oscillator. Wake-ups from sleep mode are provided every 35 msec by the 12-bit interval counter. At each wake-up the μC flips the state of its pins connected to the LCD.
| Schematic | Layout | Back view | ||
The sensor works very well and has a high repeatability. I even did not need any averaging in the program. One should note that it starts self-diagnostic from time to time and in this case its readings should be ignored. The diagnostic mode of the sensor is recognized by the msb of the very first received byte, see sensor data-sheet for details. With the current version of code the value 99 is displayed for humidity when the diagnostic is in progress.
Last modified:Mon, Jan 23, 2023.