A new display wedged into a car-based fridge

New Brains Save 12 V Fridge From The Scrap Heap

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

Bog-standard fridge internals

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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Track Those Leftovers With This Little Timer

We’ve all at some point in our lives opened the fridge door and immediately wished we hadn’t. A miasma of stench envelops us as we discover that last Saturday’s leftovers have been forgotten, and have gone off. If only we had some way to keep track of such things, to avoid such a stench-laden moment. Step forward [ThinkLearnDo], with a little timer designed for exactly that purpose.

The operation is simple enough, press the button and place the unit on top of the container with the leftovers in it. If you haven’t eaten the leftovers within a week, the LED will start blinking. The blink is a subtle reminder to deal with the old food before it becomes a problem.

Onboard is a Holtek HT68F001 microcontroller with a coin cell for power, not much else is needed. The Holtek is an unusual choice, one of several brands of super-inexpensive Chinese microcontrollers we see less commonly than ATmegas and STM32s. This is exactly the place where such a minimal computer fits perfectly:  a way to add a little bit of smarts to a very cheap item with minimal strain on the BoM.

If these chips interest you, a while back we covered a run-down of the different families including the Holtek and the famous 3-cent Padauk chips.

diy air compressor

DIY Air Compressor Made From Refrigerator And Fire Extinguisher

[Giorgos] wanted to build a pneumatic solder paste application tool but needed an air compressor to power it. Instead of going out and buying a compressor, he decided to build one himself. It sure is an ugly duckling but we’re impressed with it’s performance.

The air tank is an old spent fire extinguisher. The stock valve was removed and the insides were cleaned out. Out of curiosity, [Giorgos] figured out the volume by filling the tank with water, then measuring how much water came out. It turned out to be 2.8 liters. Two holes were drilled and threaded bungs were welded on to attach inlet and outlet lines.

The compressor portion is straight out of a refrigerator. Besides the compressor being free, the other benefit is that it is super quiet! Check the video after the break, you’ll be astonished. [Giorgos] did some calculations and figured out that his solder paste applicator needed about 8 bar (116 psi) of pressure. The refrigerator compressor easily handles that, filling the tank in 1 minute, 25 seconds.

On the output side of the tank resides a pressure switch for automatically filling the tank and a regulator for ensuring the solder paste applicator gets the required pressure. This isn’t the first time we’ve seen a refrigerator compressor used as an air compressor. Check out this dual setup capable of 400 psi.

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Single Can Mini Fridge

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What looks like a potential WMD, requires a huge power supply, and has several fans and wires dangling off the sides? Why a mini fridge of course! Your cubical buddy at work may have a Perfect Coffee Mug, or a USB powered fridge but it wont be as large of a caliber as [CaptPikel’s]. Little information about it is out thus far, but an Instructable is promised. We do however know that it uses 3 peltier coolers (assumed to be 60watt each) and can cool down to 46F while being underpowered! If only it held just a few more cans.

Brew Fridge Thermostat

thermostat-1

Reader [Will R] sent in a thermostat mod for his brew fridge. His friends had found a perfectly fine bar refrigerator and wanted to repurpose it for brewing beer. A previous batch of microbrew had been mangled by the Australian heat so they wanted something that could maintain the perfect temperature. The fridge’s built-in thermostat wouldn’t rise above 5 degrees so they had to build their own. [Will] used a 10K NTC thermistor to measure the temperature. It’s connected to an ATtiny25 microcontroller that does the comparison and determines whether to turn on the compressor. He referenced SparkFun’s relay tutorial for the switching side. Although he didn’t etch a board for this project, the design file is included along with all the code on the project site.