I wanted to be able to read the humidity from a DHT11 sensor on a ATtiny85 based project. When trying out the most common Arduino DHT11 libraries, I noticed the demo sketch alone already consumed in excess of 8 kB.
After I noticed there were false readings in the first version, I discovered some of the DHT11 pulses were not being registered by pulseIn(). Now i've modified the code:
- Check pulse length in loop cycles instead of pulseIn()
- Added temperature
- Added checksum
Tested with UNO and ATtiny85 (8 mhz)
Preview sketch size with ATTinyCore with LTO enabled, all serial output disabled:
Sketch uses 986 bytes (12%) of program storage space. Maximum is 8192 bytes.
Global variables use 14 bytes (2%) of dynamic memory, leaving 498 bytes for local variables. Maximum is 512 bytes.
At 1 mhz it almost works but some pulses are not registered. One day i'll look into timers. A interrupt based version might then also work at 1 mhz.
When not reading the humidity, the sleep current of the DHT11 was 5 uA at 5 V.
Overview:
Zoom:
After the 18 ms wake up pulse, the signal only rises slowly when not actively driven high:
