Adafruit’s Mike Barela has designed a temperature and humidity monitor built around the Atmel-powered (ATtiny85) Trinket. As Barela notes, monitoring sensors are a very common feature in current-gen Internet of Things (IoT) projects.
“While the Trinket does not have a serial monitor built in, it [does] talk over various protocols including software serial, I2C (two wire) and SPI,” Barela explained. “This project can be placed in a very small enclosure and used anywhere environmental monitoring is needed. [Plus], the code and concepts may be used in a number of your own projects.”
Aside from the Atmel-powered Trinket, key components include:
- RGB backlight negative/positive LCD 16×2 + extras
- Standard LCD 16×2 + extras
- i2c / SPI character LCD backpack
- DHT22 temperature-humidity sensor + extras/DHT11 basic temperature-humidity sensor
- Breadboarding wire bundle
- Half-size breadboard
In terms of software libraries, Barela’s project uses TinyWireM (a Trinket-compatible alternative to the Arduino Wire), TinyLiquidCrystal and TinyDHT. Meanwhile, Adafruit’s I2C / SPI character LCD backpack allows Makers to easily control the display by sending data over the two wire I2C interface.
“Standard LCDs require a large number of digital pins, [so] use of the I2C backpack reduces the pins needed considerably,” said Barela. “This project features a 16×2 display, displaying temperature and humidity without using a great deal of memory, which is important on a small microcontroller like the Trinket.”
According to Barela, the I2C backpack may be assembled and placed on the back of the display.
“The color displays have a couple of extra connectors – pins 16, 17, and 18 control the three color backlights. If you connect pin 16, the I2C will control the red light,” he continued. “You can choose to put a jumper from one of the backlight pins to backpack pin 16 to choose a different color or connect the pins high to keep them on all the time. Making the pin choice before soldering on the backpack allows you the most flexibility in choosing your backlight color, or you can just go with a ‘classic’ blue & white 16×2 LCD.”