We've had our Ooni 3 pizza oven since 2018 - back when the company was still called "uuni" and before they completed their rebranding. We use it almost every week, running it on gas rather than wood pellets, and it's been brilliant. Well, mostly...

The problem is that strong winds we experiance have a tendency to blow out the gas flame. Not only can this be dangerous, but it's also incredibly frustrating to discover that the stone has gone completely cold by the time I've noticed. This has been bothering me for quite some time, but I have finally got around to doing something about it.

The Problem

I wanted a reliable flame detection method to warn me before everything cooled down.

I have now wired up a thermocouple and connected this to my home-assistant to create an automated monitoring system.

The Hardware

I had an unused M5Stack Atom Echo lying about, which I hoped would be suitable for the job. I paired it with a K-type thermocouple from Amazon - a temperature probe that can handle the high temperatures inside a pizza oven.

Close

The wiring was mostly straightforward, though the Grove connector only has 4 pins and the MAX6675 requires 5. This meant I had to run an extra wire directly into the back of the Echo, which is a bit of a pain as it comes out at an odd angle compared to all the other wires. I connected the thermocouple to the MAX6675 amplifier board that came with the thermocouple I bought, then wired that to the Atom Echo.

I tucked the thermocouple probe into the back of the oven where it wouldn't get in the way, and left the electronics safely outside. I am not measuring the stone temperature, or any other particular temperature, but close enough to the flame that I should see any changes quickly should the flame go out.

Here is the yaml configuration I added to the atom echo in the ESPHome Device Builder:

# SPI configuration for MAX6675 temperature sensor
spi:
  clk_pin: GPIO32  # Grove SCL pin
  miso_pin: GPIO26 # Grove SDA pin

# Temperature sensor
sensor:
  - platform: max6675
    name: "Pizza Oven Temperature"
    cs_pin: GPIO25   # Spare pin - needs wire access
    update_interval: 5s
    unit_of_measurement: "°C"
    accuracy_decimals: 1
    filters:
      - median:
          window_size: 5
          send_every: 5

The Data

Here's what an evening of pizza-making looks like in numbers:

The graph shows the temperature throughout the evening. You can see the initial heating phase as the gas flame gets the oven up to temperature, reaching about 350°C. I suspect the brief gap in data when the oven was up to temperature was caused by my USB power bank going to sleep. There is some variation in temperature for most of the cooking period. Then there's the dramatic drop when we finished cooking and turned the gas off.

With this data, I think I would struggle to work out where to place an 'alarm' for detecting that the fire has gone out. During the heating, it spent all of the time above 300°C, but there was one point when the temperature dropped close to that temperature (when the oven door was open and there was a short sudden downpour of rain). I suspect if I set my alarm at 300°C, It would be susceptible to spurious alarms, as well as taking some time before triggering during a genuine flame out.

Luckily home assistant makes it easy to track a derivative value, in this case rate of change of temperature:

In this case you can see four distinct dips where the door was opened to put pizzas in and take them out. The last dip is much more dramatic the final dip, much larger is the flame out. In this case, the drop is almost instant. If I set the alarm at -0.4°C/s, it should generate an alarm within a minute of the flame out, but hopefully not get triggered by normal fluctuations.

The Fun Bit

Once I had the temperature monitoring working, I couldn't resist adding fun with the automation.

Now when I light the gas, my Home Assistant voice in the kitchen plays "The Heat Is On" by Glenn Frey from the Beverly Hills Cop soundtrack.

More importantly, when a flame-out occurs, it plays "Fire's Gone Out" by Chris Duarte Group, in this case queued up to the words "I think this fire's gone out" which seems perfect for the situation.

Next Steps

Now that I've got the basic monitoring working, there are a few practical improvements I need to make. I'll need to monitor it a few more times and perhaps tweak the alarm limits or timing to avoid spurious alerts whilst also not missing any genuine flame-outs.

I also need to create a proper enclosure for the electronics to protect them from rain, ideally finding a way to mount it permanently - but it needs to be heat resistant since the oven surface gets really hot.

I may also need to find a better portable power supply or find a way to stop the USB power bank from going to sleep.

But for now, I'm quite pleased with my musical pizza oven alarm. It's solved the original problem of not knowing when the gas had gone out, and it's added a bit of theatre to our weekly pizza evenings.