If you’re like me, you constantly find that providing clean power for cool projects can be challenging. Specifically, how best to providing power from main’s A/C (240/120VAC) to 5VDC or 3.3VDC in a tiny package.

Over the years I’ve seen various solutions offered. For many, the solution is to take wall-wart USB chargers and abuse and repackage them. For some projects this is certainly a viable and safe solution. But what is frequently not discussed is that this may not be a safe solution when embedded within a residential electrical junction box. This is because air circulation suffers, heat builds, and the result can be temps and/or voltages out of spec for what is otherwise a well functioning power source. Worse, many of these units lack advanced safety features which come highly recommended for all components embedded within our walls. This is because they were never intended to be embedded within a junction box in your wall.

Enter the HLK-PM01. When these devices first arrived on the scene, the standard advice was, ‘chineesium, so avoid them.’ As a general rule, it appears many faithfully listened. Yet at this time we have a fair amount of tests applied and can confirm they are a viable hobbyist’s power supply and can be made very safe even for embedding within a junction box in your home.

I have shamelessly ripped off some documentation to provide a concise source of information for you guys. So let me be clear, I’ve not produced any of the material here.

Test result (tested by person who tests medical equipment): https://drive.google.com/drive/folders/0B6nq_ZrOsEl7Y1NlcjBCS0s4WEU

The heart of the device is the AP8012: https://drive.google.com/file/d/0B6nq_ZrOsEl7cU9jWFI0aHA2dlk/view?usp=sharing

But to make the devices truly safe, consider adding the following inexpensive components to further increase safety. See post’s diagram for proper component use.

Thermal fuse, to be glued to the side of the HLK-PM01 module:
http://www.ebay.com/itm/5pcs-Microtemp-Thermal-Fuse-73-C-73-Degree-TF-Cutoff-Cut-off-10A-AC-250V-New-/171758798880

Ceramic slow blow fuses (250V @ 300mA):
http://www.ebay.com/itm/111433875797?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT&rmvSB=true&rmvSB=true

Varistor:
http://www.ebay.com/itm/260848704608?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT&rmvSB=true&rmvSB=true

Also, be on the lookout for impostors. They use inferior parts and are generally of poor construction quality. The tend to be noticeably less expensive (in the $1.25-$1.75 range). In this link, notice it is missing the quality control sticker and that the seal on the bottom edges are spotty at best. As this post is about a safe mains power supply, saving a buck isn’t worth it.
http://www.ebay.com/itm/HLK-PM01-AC-DC-220V-to-5V-Step-Down-Power-Supply-Module-Household-Switch-PR-/322501854061

Notice the presence of a quality controlled, ‘passed’, sticker.
http://www.ebay.com/itm/HLK-PM01-AC-DC-220V-to-5V-Step-Down-Power-Supply-Module-Household-Switch-D-/112041806450

Please note the links provided are not specific recommendations. These are links I’ve obtained based on simple searches and am providing these links for easy reference and your convenience. I know nothing of the sellers or the specific products sold by the linked vendor. Your mileage my vary.

Total power module cost should roughly be $3.40, delivered. The result is a 5v (3v3 if you get the HLK-PM03) at 600mA. This is more than enough for many arduino + nrf24l01p, arduino + esp8266 TTL, and esp8266/esp32 projects. Not only will you have a surplus of power, but you’ll have surplus safety.

Here’s another writeup on these power modules and resulting tests:
http://lygte-info.dk/review/Power%20Mains%20to%205V%200.6A%20Hi-Link%20HLK-PM01%20UK.html

And yet another look. Here, the author asserts they can pass class A EMC tests with front-end (A/C) filtering. The author has offered to make his schematic available. Which I leave as an exercise to the reader.
https://skippy.org.uk/quick-look-at-the-hlk-pm01/

If you’re really bored, read this rather lengthy thread, from which much excellent information is available. Which is where I’ve shamelessly ripped much of the content above. For brevity’s sake, I hope you’ll excuse me.
https://www.openhardware.io/view/13/In-Wall-ACDC-Pcb-for-MySensors

An actual IoT project built around the HLK-PM01:
https://www.mysensors.org/hardware/in-wall-relay

Edit:
Video review:
https://www.youtube.com/watch?v=zrxekAJ_M1I

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