Raspberry PI 4: PoE with LM2596

During last Black Friday I bought Raspberry PI 4 on Aliexpress for just $36. After initial tests I’ve found out that a good cooling case is definitely a must have. The SoC quickly reaches 80°C under a full load and then throttles from 1.5 to 1.0 GHz per ARM core to maintain the temperature limit. So, I ordered a very nice Chinese aluminium case for just $7.5. I love PoE devices – my new toy must also support Power over Ethernet – and it does!

I took a cheap LM2596 DC converter and installed it together with the board in the aluminium case.

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Laptop upgrade: Dell Latitude E7440 → E7270

I have been using my Dell Latitude E7440 laptop (i7-4600U / 16 GB RAM / 480 GB SSD) literally every single day for almost 6 years. I still say this is one of the best laptops ever built. I’ve been looking for a upgrade for quite a long time though. However, I could not wait any longer, because my current laptop would require some expensive investments, including new:

  • High-capacity battery – that would be the third one (original $100).
  • Keyboard – that would be also the third one (original $50).
  • LTE Cat 6 miniPCIe module – to replace the Cat 4 modem ($100).
  • Some case elements – e.g. bottom cover with rubber feet, but also palmrest w/ touchpad in the near future…

In fact, no wonder that I could not find anything suitable for a very long time, because my requirements for a new laptop were very detailed and specific. 

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MikroTik RouterBOARD hardware disappointment

I’ve been lately looking for a small 10/100M Ethernet switch with a USB and both PoE input and output port (Power over Ethernet). The MikroTik RouterBOARD hAP (RB951Ui-2nD) looked pretty good, so I ordered one. The 2.4 GHz Wi-Fi interface was unnecessary, but the price was acceptable anyway, as I found a used device in excellent condition at just $25 including shipping.

As usually, the first thing I did after receiving the package was the teardown. The PoE ports are usually dedicated for some remote devices connected with long Ethernet cables and located outdoors. Therefore, a special protection should be included in the front of the controller (QCA9531 SoC in hAP). Unfortunately, this is not the case of RB951Ui-2nD. Although the engineers designed the PCB of this device with TVS diodes on both PoE input and output ports, the final product does not contain them. Protection for other ports was not planned at all.

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Arduino Uno R3 failure

Recently I’ve got a genuine Arduino Uno R3 from my friend to repair. The problem with his board was actually very generic – it has just stopped working. Personally, I don’t buy such boards, because  they are extremely overpriced. I have been using several Chinese clones around for years and I have not encountered any problems so far.

At first sight, the USB interface was working fine and the board was detected by the system without any problems.

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