Darian Johnson’s 2018 Compost Professor DIY build uses a temperature probe and capacitive moisture sensor to monitor a compost pile, then connects those readings to an Alexa-based guidance system. It is a hands-on electronics project—not a ready-made monitor—and the tutorial’s Alexa service and component compatibility have not been confirmed as current.
What the Compost Professor hardware monitors
The probe is designed to record compost temperature and moisture. The broader Compost Professor system uses those inputs to offer guidance on what to add, when to water or turn the pile, and when compost may be ready. Project author Darian Johnson described it as “an easy do it yourself version of the Compost Professor that integrates with Alexa.” Read the Hackster.io project (published September 15, 2018).
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The tutorial describes an Alexa skill and cloud workflow. It is historical documentation: current Alexa skill or API operation, library compatibility, and availability of replacement parts have not been established, so check those before committing to the build.
The Tool Desk
Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →Parts and tools in the tutorial
The author’s listed electronics and enclosure components include:
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- Easy to Operate for Home Composting, Gardening, Schools & Community Programs
- Rugged Stainless Steel Construction
- Long 15" Stem with Thick 5/16" Diameter
- User Calibratable, 0-10 Wetness Scale
- Instant Readings Powered by One AAA Battery (Included)
- Epoxy-coated thermistor; the author says its resistance and Beta Coefficient must be known. Adafruit part 372 is given as an example.
- DFRobot capacitive moisture sensor.
- Adafruit Feather M0 WiFi board.
- Texas Instruments TPL5111 low-power timer.
- Custom-fabricated PCB, assorted resistors, LiPo battery, and enclosure.
- For the deeper printed-probe option, a five-pin weatherproof connector.
These are the 2018 tutorial’s specifications, not confirmation that those exact parts remain available or work with current services and software. Before substituting, check electrical characteristics, dimensions, interface, and code support. The author notes an ESP32 could fit the board footprint but would require the builder to write their own code.
Choose an enclosure approach
| Approach | Probe reach | Sensor replacement | Build considerations |
|---|---|---|---|
| Weatherproof container | More limited, according to the author | Not stated in the project description | Presented as the lower-cost option |
| 3D-printed probe/enclosure | Allows deeper placement | Weatherproof connector lets the moisture sensor be changed if it corrodes | Requires printing and assembly; the author recommends ASA for long-term compost exposure and warns PLA will degrade |
The material advice is the project author’s guidance and was not independently tested. Either route involves wiring and soldering; the tutorial also discusses sealing probe openings with hot glue and avoiding solder bridges around the low-power timer.
Quick Recap
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- Digital Deluxe
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- Perfect for Large Compost Piles
- Rugged Metal Construction with T-handle
- Extra Long 36" Stem with Thick 5/16" Diameter
- Calibrates to Your Soil or Compost, 0-10 Wetness Scale
- Powered by One AAA Battery (Included)
Rank #2
- Longer 24" Length Perfect for Trees or Deeper Pots
- Rugged Metal Construction with T-handle
- Thick 5/16" Diameter Stem
- Calibrates to Your Soil or Compost, 0-10 Wetness Scale
- Powered by One AAA Battery (Included)
Build and configure the system
- Assemble the electronics and probe. Wire and solder the sensors, timer, board, and battery as shown in the project instructions. Seal probe openings as directed; take care around the timer’s closely spaced connections.
- Set up the Alexa skill. The author’s instructions have the builder obtain an API key through the skill. Verify that the skill and required API are still available before relying on this workflow.
- Enter pile details. The tutorial asks for a ZIP code for weather-forecast context, whether the bin is open or closed, and the bin’s dimensions.
- Allow readings to accumulate. The 2018 author says the device takes measurements every 30–45 minutes and needs about four days of data before recommendations begin. These are the author’s stated design instructions, not independently verified present-day results.
What to verify before starting
- Whether the Alexa skill, API, and cloud workflow described by the 2018 project remain operational.
- Whether the tutorial’s firmware and libraries support the board and components you can obtain.
- Whether substitute sensors match the required electrical behavior, physical dimensions, and code expectations.
- Whether you can complete the soldering, sealing, and enclosure work; this is a maker build, not a plug-and-play appliance.
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