A new display wedged into a car-based fridge

New Brains Save 12 V Fridge From The Scrap Heap

March 14, 2024 by Dave Rowntree 17 Comments

Recently [nibbler]’s Evakool 55L vehicle fridge started to act strangely, reporting crazy temperature errors and had no chance of regulating. The determination was that the NTC thermistor was toast, and rather than trying to extricate and replace this part, it was a lot easier to add a new one at a suitable location

A straight swap would have been boring, so this was a perfect excuse for an overboard hack. Reverse engineering the controller wouldn’t be easy, as the data wasn’t available, as is often the case for many products of this nature.

While doing a brain transplant, the hacker way, we can go overboard and add the basics of an IoT control and monitoring system. To that end, [nibbler] learned as much as possible about the off-the-shelf ZH25G compressor and the associated compressor control board. The aim was to junk the original user interface/control board and replace that with a Raspberry Pi Pico W running CircuitPython.

For the display, they used one of the ubiquitous SH1106 monochrome OLED units that can be had for less than the cost of a McDonald’s cheeseburger at the usual purveyors of cheap Chinese electronics. A brief distraction was trying to use a DS18B20 waterproof thermometer probe, which they discovered didn’t function, so they reverted to tried and trusted tech — a simple NTC thermistor.

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Solder Two Boards At Once With This Dual Reflow Plate

November 10, 2023 by Dan Maloney 4 Comments

Homebrew reflow projects generally follow a pretty simple formula: find a thrift shop toaster oven or hot plate, add a microcontroller and a means to turn the heating element on and off, and close the loop with a thermistor. Add a little code and you’re melting solder paste. Sometimes, though, a ground-up design works better, like this scalable reflow plate with all the bells and whistles.

Now, we don’t mean to hate on the many great reflow projects we’ve seen, of course. But [Michael Benn]’s build is pretty slick. The business end uses 400-watt positive temperature coefficient (PTC) heating elements from Amazon controlled by solid-state relays, although we have to note that we couldn’t find the equivalent parts on the Amazon US site, so that might be a problem. [Michael] also included mechanical temperature cutoffs for each plate, an essential safety feature in case of thermal runaway. The plates are mounted at the top of a 3D-printed case, which also has an angled enclosure for a two-color OLED display and a rotary encoder.

The software runs on an ESP32 and supports multiple temperature profiles for different solder pastes. The software also supports different profiles on the two plates, and even allows for physical expansion to a maximum of four heating plates, or even just a single plate if that’s what you need. The video below shows it going through its paces along with the final results. There’s also a video showing the internals if that’s more your style

We appreciate the fit and finish here, as well as the attention to safety. Can’t find those heating elements for your build? You might have to lose your appetite for waffles.

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An opened plastic project box with electronics inside

Smoking Meat Finds Natural Home In The Cloud

August 9, 2022 by Chris Wilkinson 15 Comments

Did you know that backyard barbecues now come with WiFi? It should be no surprise, given the pervasiveness of cloud-enabled appliances throughout the home. However [Carl] wasn’t ready to part with his reliable but oh-so-analog BBQ smoker, so instead he created an affordable WiFi-based temperature monitor that rivals its commercial counterparts.

Accurate temperature measurement is essential to smoking meat from both a taste and safety standpoint. In this project, two Maverick ET-732/733 thermistor probes take care of the actual temperature monitoring. One probe is skewered into meat itself, and the other measures the ambient ‘pit’ temperature. Combined, these two gauges ensure that the meat is smoked for exactly the right length of time. [Carl] mentions that adding an extra temperature sensor is trivial for larger setups, but he’s getting by just fine with two data points.

Naturally an ESP8266 does most of the heavy lifting in bridging the gap between smoke and cloud. At the core of this project is utility and practicality – temperature statistics can be viewed on any device with a web browser. Being able to study the temperature trends in this way also makes it easier to predict cooking times. Electronic alerts are also used to notify the chef if the temperature is too hot or cold (among other things). The entire contraption is housed in a smart looking project box that contains an LCD and rotary encoder for configuration.

If this has piqued your culinary interest, check out the extensive documentation recipe over on GitHub and the project Wiki. We also recommend checking out this project that takes automated meat smoking to the next level.

Test For 3D Printer Runaway

September 1, 2021 by Al Williams 22 Comments

A few 3D printers have had a deserved reputation for bursting into flames. Most — but apparently not all — printers these days has firmware that will detect common problems that can lead to a fire hazard. If you program your own firmware, you can check to see if you have the protection on, but what if you have a printer of unknown provenance? [Thomas] shows you how to check for a safe printer. Also check out his video, embedded below.

The idea is to fake the kind of failures that will cause a problem. Primarily, you want to have the heaters turned on while the thermistor isn’t reading correctly. If the thermistor is stuck reading low or is reading ambient, then it is possible to just drive the heating element to get hotter and hotter. This won’t always lead to a fire, but it could lead to noxious fumes.

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Practical Sensors: The Many Ways We Measure Heat Electronically

February 19, 2021 by Al Williams 24 Comments

Measuring temperature turns out to be a fundamental function for a huge number of devices. You furnace’s programmable thermostat and digital clocks are obvious examples. If you just needed to know if a certain temperature is exceeded, you could use a bimetalic coil and a microswitch (or a mercury switch as was the method with old thermostats). But these days we want precision over a range of readings, so there are thermocouples that generate a small voltage, RTDs that change resistance with temperature, thermistors that also change resistance with temperature, infrared sensors, and vibrating wire sensors. The bandgap voltage of a semiconductor junction varies with temperature and that’s predictable and measurable, too. There are probably other methods too, some of which are probably pretty creative.

Bimetalic coil by [Hustvede], CC-BY-SA 3.0.

You can often think of creative ways to do any measurement. There’s an old joke about the smart-alec student in physics class. The question was how do you find the height of a building using a barometer. One answer was to drop the barometer from the top of the building and time how long it takes to hit the ground. Another answer — doubtlessly an engineering student — wanted to find the building engineer and offer to give them the barometer in exchange for the height of the building. By the same token, you could find the temperature by monitoring a standard thermometer with a camera or even a level sensor which is a topic for another post.

The point is, there are plenty of ways to measure anything, but in every case, you are converting what you want to know (temperature) into something you know how to measure like voltage, current, or physical position. Let’s take a look at how some of the most interesting temperature sensors accomplish this.

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Designing Printed Adapters For Power Tool Batteries

March 30, 2020 by Tom Nardi 26 Comments

Unless you’re particularly fond of having multiple types of batteries and chargers, you’d do well to make sure all your portable power tools are made by the same company. But what do you do if there’s a tool you really need, but your brand of choice doesn’t offer their own version of it? Rather than having to buy into a whole new tool ecosystem, you might be able to design your own battery adapter.

Note the locking tab that’s been printed separately.

As [Chris Chimienti] explains in the video after the break, the first thing you’ve got to do (beyond making sure the voltages match) is take some careful measurements of the connectors on your batteries and tools. His goal was to adapt a Milwaukee M12 battery to Makita CXT tool, so if you happen to have that same combination of hardware you can just use his STLs. Otherwise, you’ll be spending some quality time with a pair of calipers and a notepad.

Once the interfaces have been designed and printed, they are wired together and mounted to opposite ends of the center support column. In theory you’d be done at this point, but as [Chris] points out, there’s a bit more to it than just wiring up the positive and negative terminals. Many tools use thermistors in the batteries for thermal protection purposes, and when the tool doesn’t get a reading from the sensor, it will likely refuse to work.

His solution to the problem is to “hotwire” the thermistor lead on the battery connector with a standard resistor of the appropriate value. This will get the tool spinning, but obviously there’s no more thermal protection. For most homeowner DIY projects this probably won’t cause a problem, but if you’re a pro who’s really pushing their tools to the limit, this project might not be for you.

Of course, this isn’t the first time we’ve seen somebody adapt batteries from different brands to work on their tools. It’s a common enough problem once you start building up a workshop, although you could always avoid it by building all your own tools.

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Proprietary Fan Blows, Gets PWM Upgrade

October 26, 2019 by Bryan Cockfield 13 Comments

Proprietary components are the bane of anyone who dares to try and repair their own hardware. Nonstandard sizes, lack of labeling or documentation, and unavailable spare parts are all par for the course. [Jason] was unlucky enough to have an older Dell computer with a broken, and proprietary, cooling fan on it and had to make some interesting modifications to replace it.

The original fan had three wires and was controlled thermostatically, meaning that a small thermistor would speed up the the fan as the temperature increased. Of course, the standard way of controlling CPU fans these days is with PWM, so he built a circuit which essentially converts the PWM signal from the motherboard into a phantom thermistor. It’s even more impressive that it was able to be done with little more than a MOSFET and a Zener diode.

Unfortunately, there was a catch. The circuit only works one way, meaning the fan speed doesn’t get reported to the motherboard and the operating system thinks the fan has failed. But [Jason] simply disabled the warning and washed his hands of that problem. If you don’t want to use a CPU fan at all, you can always just dunk your entire computer in mineral oil.