So you've been composting for a bit now and things are going ok. You've been regularly turning the compost, but you have no idea if all this work is even worth it because you don't even know what's going on in there. You try to split the dry material and wet material 50/50 but some days it's rainy and others it's dry. Is it even heating up? Do you really have to stick your hand in last weeks spaghetti leftovers to tell? What if there was a way to know all the info you want to know about your compost and how to improve its health without ever touching or looking at it?

Good news! You can use a Circuit Playground Express and some extra goodies to tell you exactly what you want to know about your compost: when to add more food scraps, more dry material, and when to turn it.

This is a part II to the first guide on building a compost tumbler to more easily aerate your compost. Even if you have your own tumbler, I suggest skimming through that guide to get an understanding to why we would want to "optimize" compost.

As mentioned in the previous guide (to compost aerobically), we want to aerate compost every so often to feed oxygen to the microbes and other organisms within the compost so they can continue to break down the food scraps. Even though a tumbler makes it easier to turn compost, we don't want to be turning it more than we have to. Furthermore, solely turning the compost isn't always going to be the answer to making our compost healthier. Here are the primary situations when we need to adjust the compost:

  • When the compost is too dry, add some food scraps and turn it.
  • When the compost is too wet, add some dry carbon material like leaves, wood chips, or paper and turn it.
  • If the compost isn't heating up, turn it.


Typically, the compost should have about half dry and half wet material within. However you can't always tell how much of each material is present within your container. Thus we can use a moisture sensor to gauge how wet or dry the compost is. 


Due to the energy the organisms within the compost breaking down the food scraps release, the compost gets HOT. At optimal state, the compost should be at 135 - 160 degrees Fahrenheit.  We will use a temperature sensor to gauge how hot the compost is and adjust accordingly.


Prerequisite Guides

If you've never worked with CircuitPython, a CPX (Circuit Playground Express), or soldered, I suggest reading through these guides before continuing. 

This guide was first published on Aug 29, 2018. It was last updated on Aug 29, 2018.
This page (Overview) was last updated on Jun 09, 2020.