Bluetooth Greenhouse on an ATtiny85 using 2 DHT22 humidity/temp sensors.

So I have just shrunk a project on to an ATtiny85 PIC.

The greenhouse gets power from a 20Ah battery with a 20W solar panel (about 0.5A during spring sun...).

It is a simple greenhouse monitoring system.

The ATtiny85 has 5 I/O pins:

  • 3 of which have dual digital and ADC (Analog->Digital Converters) for reading voltage output based sensors
  • 2 are digital/PWM outputs

I have used 2 digital pins for the DHT22 sensors. These read humidity (RH%) and temperature one one pin each. One sensor inside the greenhouse and one threaded through the greenhouse wall.

I have an LDR (145ohm->150kohm) with a 330 ohm resistor as a light sensor. I know it is no light->frequency sensor...but I only wanted to see where "day and night" kinda is on graphs on 1 analog pin.

I have used an HC-05 bluetooth module with an external aerial (some piano wire @ ~5") to communicate with a raspberry Pi in the house which takes the data and puts it in a .csv (excel) file ready for plotting using liveplot or the excel tools. The very DIY aerial made the link about 20meters :).

I can the use FTP to get the data and monitor from wherever I am (a quick python script that will read the last line of the file for me makes a quick program I can run when I am not home).

I have used 4 pins so far...3 digital and 1 analog. I am planning on possibly using the last as either:

  • A) software-serial to a second ATtiny to run loads of stuff.
  • B) more likely just a fan system to cool my greenhouse when the temp gets too high.

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Looks nice