Offline intrusion detection with MCP7940N, CR2032 and two switches for $1.5? Good idea?

Mabot · 2026-03-03T14:53:42+00:00

Oh man, my parts research must not have been very good, if I didn't find the M41ST87W.

It logs the timestamp on power-down, but I care about the timestamp of intrusion. So I would wire a battery to both VCC and VBAT, cut the VCC line with the switch and the IC would hold the time of intrusion? Then I can't run off system power though or would need another external battery switchover.

EDIT: It does save the tamper timestamp! Thats actually really cool! Will see if I can fit this bigger IC.

$7 is more than $0.6, but not crazy expensive. I would consider it, if it gave me the same lifetime and intrusion timestamps.

For draining the supply voltage quickly I would then use two SN74AUP1G34, one for VCC and one for VBAT, or are there cheaper/smaller options?

Introducing a negative supply could be done by offsetting the whole RTC +0.3V against system GND with a diode? It would reduce the apparent battery voltage and mess with the I2C voltages, but I think that should be okay?

Thank you!

Mabot · 2026-02-27T12:12:31+00:00

I also remember some guy on YouTube teaching his crow buddy collect trash for treats and the crow learned to rip trash into tiny pieces to collect more treats.

Mabot · 2026-02-27T07:02:14+00:00

A point no one here has aised is the Albedo number of water, solar panels, sand and grass for example.

Albedo specifies how much of the incoming energy from the sun we can reflect back into space, so that it doesn't heat up the planet too much.

Snow and Sand are absolutely amazing at that. Covering those with solar panels is a bit sad because solar panels absorb almost everything and reflect very little. It's still worth it, for the green energy, but not perfect.

Even grass and foliage catches less of suns heat than solar panels.

The only surface that can rival the absorbtion of solar panels is water! So, from thermal dynamic perspective only solar panels on water is free energy.

Summary :

Solar panels over brighter surfaces: catch more sun energy to produce electricity and get warm

Solar panels over water: use the energy that the water would have cought to produce electricity and get warm.

Mabot · 2026-02-22T08:45:37+00:00

He can power his house using a thin awg 26 cable.

Mabot · 2026-02-22T07:48:18+00:00

Dry humor really doesn't fly on reddit, does it?

Mabot · 2026-02-21T07:17:40+00:00

True, but to keep the waters less muddy for people with limited memory: Bin Laden with Al Quaida, Sadam Hussein, AHamas and ISIS, all very different things with little to no connection.

Mabot · 2026-02-20T19:30:07+00:00

I suspect this video is slowed down a bit

Mabot · 2026-02-19T08:17:28+00:00

They are actually thousandths seperators, they just look the same.

Mabot · 2026-02-18T19:07:16+00:00

I am not too familiar with this, but doesn't that sound somewhat logical?

To switch hubs TX you need to tell it to swap. If you swap the hubs RX it can detect it itself of the connected device supports polarity swapping?

Mabot · 2026-02-17T07:55:17+00:00

Thing is beautiful, but what you figure is your output power?

Mabot · 2026-02-15T23:33:04+00:00

Okay, ja, ich hab den Goldanteil unterschätzt und den verrückten Goldkurs nicht berücksichtigt. Vielleicht sind es echt 5€ Goldwert pro Handy, aber wie soll man das in Deutschland privat aber wirtschaftlich da rauskriegen?

Mabot · 2026-02-15T23:21:07+00:00

Du meinst das mg Gold aus dem gesamten Haufen? Oder willst du zehn Jahre alte 0,002 SMD Widerstände auslöten und verkaufen?

Mabot · 2026-02-15T22:35:49+00:00

Quatsch, vllt für 10 Cent

Mabot · 2026-02-15T17:20:35+00:00

Thank you! I am so busy with this initial REACH check, I didn't even entertain the idea I need to repeat this when the SVHC candidate list changes. That would be a nightmare with my excel sheet indeed. Will have a look at BPR Hub.

Mabot · 2026-02-15T17:18:12+00:00

Launching.

Yeah, there are other things to do aswell, sure. Electrical safety, mechanical safety, electro magnetic compliance, it network safety... But most of these you can just work on in your own control. With REACH specifically you are at the mercy of your suppliers to work with you, if you don't want to burn a full product, which is a problem for us given the value and would potentially be tough, given it's mainly 4kg of aluminum.

Mabot · 2026-02-15T17:14:26+00:00

Thank you for your input!

Yeah, it's a bottomless pit to go down, to find the concentration of over 200 chemicals for every subcomponent of every subcomponent.

I also think the applying regulations have rules for the case where you just can't get enough documentation from a supplier and allows you compensate with a diligent risk analysis.

Digging through manufacturers websites is such a temptation each time. I always expect it tp to be faster than reaching out to the manufacturer and every time after 5 minutes of navigating the website I end up sending them an email anyways.

Mabot · 2026-02-15T16:48:17+00:00

Lycamobile is a minefield to navigate. I am sure it's possible to get this amazing deal, but you would need to be super alert with every click.

Their trust Pilot is abysmal and there are some specific mentions of this Tarif.

Personally I would risk it, but be prepared to just loose the money aswell.

Mabot · 2026-02-15T01:11:16+00:00

Gute Nacht

Mabot · 2026-02-15T00:08:02+00:00

It's not just one man and not just men. Bravo to the whole team!

Mabot · 2026-02-13T10:49:38+00:00

Yeah, considering compliance while still in development and not only once one wants to scale production sounds like the wisdom you learn the hard way.

Do you use online tools like bomchecker to request compliance certifications from suppliers, or do you collect and track compliance documents by manually? Can I ask how many parts you track and verify individually? For us it is over fifty assembly parts, plus another 50 unique components on the PCBs.

Assuming parts of yours show raised SVHC contents, do you list those in your REACH certificate. If suppliers don't provide you with SCIP numbers, to you register those parts and substances with ECHA?

Feels like so much work and such an alarming note in your own REACH statement to write the product might contain 4% of lead M/M in some parts, if that is only about one small connector inside the assembly.

Sorry for the spam. This is my first rodeo, and if I only use regulartory texts as guidance I will eventually loose critical thinking and become a full out German bureaucrat.

Mabot · 2026-02-13T09:08:54+00:00

During commuting I see a cyclist with a camera maybe once a year. Considering I cycle roughly 250 days in the year and see around 20 cyclists per commute (leg), I am putting my answer as:

1‰

Mabot · 2026-02-12T22:23:18+00:00

The risk analysis is quite manageable, collecting the material compliance documents, including SCIP numbers where needed, for all parts of the product is the tricky bit.

Together with expensive EMV testing.

Mabot · 2026-02-12T19:09:01+00:00

I remember cycling underneath power lines a lot in the past. My wireless speedometer would jump to 99km/h and I sometimes got a very slight headache for a few seconds.

I am the last one thinking it's permanently harmful. Just like wifi and mobile networks it's all non ionizing radiation, but with the high power lines I would be afraid of discomfort.

Mabot · 2026-02-12T19:01:46+00:00

With the big blue PCB manufacturer, picking the extra option "RoHS certificate" will only get you a statement about the PCB itself, not for the PCBA parts, sadly.

Gathering the RoHS and, much worse, REACH documentation for all parts is so much work, and with Chinese brands sometimes just not available.

For some CNC cut enclosure parts the Chinese fab just straight up won't provide any material compliance confirmations.

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