LEDs at Elevated Temperature

Visitor said:

Just to cut off any helpful suggestions... the Instant Pot pressure vessel is metal with a tight seal to hold steam pressure and may not be penetrated. Temperature measurements on the wall of the pressure vessel to not reflect what's happening with the product inside, so that's not helpful.

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gophert said:

Use an ESP32 or ESP8266 and you can send WiFi or Bluetooth signals instead.....

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Visitor said:

I don't know that RF would get out of the pressure vessel. There is a silicon gasket, so it's not a total metal-metal seal, but the lid overlaps the gasket.

I suspect the temperature rating of an ESP32 doesn't approach 125°C. Have to look that up.

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gophert said:

I can confirm LEDs can survive some amazing temps and pressures. Color may shift if you get too hot but it is more difficult than you think to kill a 5mm indicator LED - especially the red ones.

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Visitor said:

I'm using suface mount 0603s, in yellow and red (green is marginal on my battery voltage). I'm adding patterns for through-hole LEDs if the surface mount ones don't survive.

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Visitor said:

I can't design a microcontroller circuit without an LED to flash!

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Visitor said:

I want to make a few measurements inside a jar of food product, inside a commercial Instant Pot. Permanently modifying the lid for a possibly one-time experiment is undesirable and penetrating the thin metal canning lid might invalidate the experiment.

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Visitor said:

Not that I don't appreciate the help and guidance, but my question was and remains to be how indicator LEDs will perform at elevated temperatures. That they are in a pressure cooker water bath is useful information because it means that the temperature cannot go beyond the specified temperature even for an instant.

The specific question was intentional. Too often I see people ask questions here, and rather than the question being addressed, their idea is torn apart, redesigned to be the way "I would do it", their motives questioned, etc. People may want to "do their own thing their way" even though it's not necessarily the best or easiest way to accomplish something.

All of that being said, here's what I am researching. In years past, "county extension agents", often working in conjunction with state universities, had programs to advice people on cooking techniques and food safety, gardening issues and other "home ec" areas. With changing lifestyles, changes in government funding and etc, these programs have been less active.

One of their large areas of expertise was in home canning – it's in the government interest to prevent people dying from botulism due to improper canning techniques and home canning of inappropriate foods. Depending on what's being canned (where the can is actually a glass jar), canning has been done in an open boiling water bath or a pressure cooker if a higher temperature is needed for the "kill step", which depends on time and temperature. For different foods and the types of bacteria that will grow in them, certain temperatures must be reached and maintained for certain time periods. If a higher temperature can be achieved, the food can be held at that temperature for a shorter period of time. Time and temperature charts have been developed for canning in pressure cookers, as their behavior is well understood and documented. Apply enough heat and maintain a pressure of X and the temperature will be Y. This is simple physics and is always true.

"Instant Pots" are the latest cooking craze – crock pot and pressure cooker all-in-one. But there is an unknown about these, resulting in extension services making the recommendation that they not be used for canning. It is unknown if the "smart" control system actually maintains a constant temperature during pressure cooking. Does the control system try to use as little energy as possible and keep the heat input to the minimum level necessary to maintain the pressure, and possibly cycle above and below the required temperature as it does so? If the 110°C temperature required to maintain a particular pressure cycles cycles around 110°C instead of always being 110°C as guaranteed by an adequate thermal input, the safety of the kill step is lost. This is the kind of research extension services used to do, but since nobody is doing it, the recommendation is that Instant Pots are unsafe for canning.

So the question is documenting the temperature over a period of time. The particular question – is it safe to home can tuna in an Instant Pot. What is the temperature profile in the center of a pint jar filled with tuna over a processing time of about 4 hours? Data should be logged often enough to provide a detailed temperature profile over a 4 hour span. Because a sample size of one doesn't provide proof of anything, the test needs to be repeated in different brands and types of Instant Pots to verify results. My partner is a foodie in a community of foodies, so the knowledge and interest to research the problem thoroughly exists.

Designing a data long for 125°C isn't too difficult, aside from a few issues:

¤ Power: Panasonic BR2450A lithium coin cell is spec'd to 125°C, and provides 550mAH at 3 volts.

¤ Crystal: Crystals rated for high temperature are available.

¤ LEDs: If run of the mill LEDs last though a few processing cycles, great. If not, it's just a little less certain that data logging is actually occurring during a given run.

I'm planning to have these assembled at JLCPCB. Micros in their parts assortment in the industrial temperature range are limited, but fortunately, the selection includes the PIC28F24/226F1K22-E/SS. For the temperature sensor, I'm using Microchip's MCP9808. A EEPROM rated at 125°C completes the circuit.

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