Build a kiln monitoring device

Drop-and-hold and slow-cool firings are so important yet they are outside the abilities of so many companies and potters that do not have electronic controller-equipped kilns. The actual firing schedule experienced by ware in a kiln can be very different from the one programmed into the controller. Many glazes depend on specific schedules, when these go wrong it is important to have a record of what happened in the kiln to diagnose the problem.

We are building this monitoring device for a parts cost <$100, it will be able to archive firing curves into your insight-live.com account. This is not a kiln controller. You will be able to view a history of firings or view them live and compare with a target curve. This will be invaluable when developing manual switching schedules to match a curve. All of this will be possible without disturbing the controller already on the kiln.

We are using an ESP32 microcontroller (but remember, we are not building a controller, it is a data logger or monitor). This has plenty of power for excellent functionality and storage. These ESP32 devices have a wifi antenna, enabling interaction using any device with a browser, but they do not have an operating system that can be hacked from an external source. This device will only send data to an online API at Insight-live.com, all interaction will be done there, totally out-of-band. It will not have any "push" technology, no outside source will be able to give it any kind of command. That being said, it will have the ability, on its own, to access the API to get information. The complexity of this device will thus be kept to an absolute minimum, just enough to recognize the commencement of a firing and sending measurement data at defined intervals. That will enable us to put all the ease-of-use development effort into the web page that reports the measurements of the monitor.

Related Information

Kiln Firing monitor - Going in the wrong direction

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So many glazes appear as they do because of the firing schedule (especially the cooling curve). Imagine getting an awesome result out of a kiln and not knowing (or being able to replicate) the exact firing schedule that produced it. Or a bad result and being able to relate that to the firing schedule that actually occurred. This is not a kiln controller, it simply reads and records the temperature once per minute. It is a Raspberry Pi computer with camera that reads the temperature display on the kiln (using machine vision). This seemed like a good idea at the time, but adding all the difficulties of reading the display turned out not to be worth the trouble when it is so easy to connect a dedicated thermocouple. Further, the device is too capable. Being an entire Linux computer it would be a vector for hacker intrusion into the host wifi network unless being constantly updated (a large Las Vegas casino was hacked recently, the vector into their network was an iOT aquarium thermometer). While it can be programmed as an access point, hosting its own wifi network, this is too much trouble to use, people are not going to want to constantly change their wifi connection. More problems: Its complexity means there are too many things to go wrong, it uses too much power for battery operation and is a hassle to plug in. Most importantly, the computer knowledge required is well beyond the ability of the average person to navigate.

All the parts to develop a kiln monitoring device

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These are all very inexpensive and easily available.

2.4" 240x320 TFT Touch Display
ESP32 controller (a wifi-equipped computer on a chip)
MX6675 thermocouple interface and thermocouple
Prototyping breadboard with wire interconnects
Breadboard Power Supply Module 3.3V/5V

When the prototype is working we will incorporate the software into a ready-made, battery-powered device that uses this same controller chip. It is likely that the display will not be needed for logging operations, the device will simply watch for temperature rise and automatically begin recording when that happens.

Final logging device configuration

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Here are two options for the packaging in the final logging device. The one with the larger screen is of course much more expensive, ~$50. The device with a small 1-inch screen should cost much less, it would have the same computation and communication abilities. We could make the software work on both and both.

The screen will likely be used for simple status information to assure the device is running and recording. Both devices have a button, it may be possible to use this to initiate recording of a firing. Both of these are available without a display, it may not be needed once we are assured of reliable operation (its absence would greatly extend battery life). That being said, a display might be handy to show firing or switch-setting schedules as a reference for programming the controller on the kiln.

Inside a kiln with a Bartlett Genesis controller

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A Bartlett Genesis kiln controller circuit board

Notice the 220V enters lower left to a terminal block. That splits to a transformer (above) and relays (below that). The 4-07-6024 transformer supplies power to the SMT_3140 controller board (converting the 220V down to that needed by the circuit board). The controller is run by an MSP430 Texas Instruments microcontroller (lower left has closeup). That controller has inputs from the thermocouple and a current monitor (yellow donut shape around the wires going to the elements). The board has outputs that connect to the relay, that relay in turn controls the flow of current to the elements. This is a very simple appearing device, but not something to be replaced lightly. DIY controller boards documented online look tempting but they are not CSA or UL approved (so your fire insurance coverage is implicated). Commercial controllers focus on safety and liability over functionality, they handle intermittent thermocouple connections, bad thermocouple readings, stuck relays and shorted and weak elements - these are runaway conditions that could become meltdowns in a kiln controlled by a DIY device. This being said, these commercial products do have a weakness: The relays. They are mechanical devices and are the first thing to need replacement. Kiln controllers are thus particularly good at recognizing relay failure.

Links

Glossary	Firing Schedule Designing a good kiln firing schedule for your ware is a very important, and often overlooked factor for obtained successful firings.
Glossary	Drop-and-Soak Firing A kiln firing schedule where temperature is eased to the top, then dropped quickly and held at a temperature 100-200F lower.
Glossary	Kiln Controller In ceramic kilns the firing schedule is typically managed automatically by an electronic controller. But that may not mean that ware gets automatically fired to the correct temperature and atmosphere.
Typecodes	Kiln Controller Device List If you are aware of devices not listed here please contact us. We want to focus on those in active development. Devices supplied on manufactured kilns are usually relabelled, they are not actually made by the kiln manufacturer.

By Tony Hansen
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