The temperature, humidity and barometric pressure sensors have been changed to the Bosch BME280 integrated environmental sensor.

Reasons:

• One sensor instead of two components, means lower cost, needs less space, and consumes less power
• The energy hungry I2C interface has been changed to SPI
• The BME280 provides absolute pressure sensing (while the former LPS25 needs calibration)

In the original concept it was planned to 'estimate' the UV Index using an si1132 sensor. Long, torturous development lead to a divorce from this idea, however;

some reasons:

• si1132 measures visible light, then estimates the UV index; this can be very inaccurate in cloudy situations (according the datasheet as well)
• The new sensor (ML8511) measures true UV radiation
• The I2C interface should be dropped, as it's too energy hungry
• The si1132 needs a complicated driver which is memory and energy inefficient

More things about the si1132 operating method:

• The I2C interface is not static, it has a minimum clock frequency requirement...

Totally unacceptable! With a slower MCU, using software or semi­-software I2C interface this can't be used! Usually I2C and SPI interfaces are static, can be driven as slow as you want.

• The command operation expects a strange trial­error method. According to the datasheet you give a command, then you have to check whether it has been processed. If it has not been processed after several ms, it has to be repeated. What???? It's a very energy consuming process! Anyway we are talking about a digital interface which should process commands, but it acts more like a spoiled princess...

So say good by to si1132 (sorry Silicon Labs...)

Say hello to ML8511!