Show HN: Capacitor Alarm Clock | Hacker News Reader

Show HN: Capacitor Alarm Clock

github.com

153 pointsarcaege48 comments

I made an alarm clock that blows up capacitors to wake you up.

There are more details on the Github repo but it's made from an esp32-c3 as the microcontroller, with 3 capacitor slots. There are relays on each capacitor slot to put 15v reverse voltage on the capacitor, with 5.1 ohm resistors on each slot for current limiting in case the capacitor shorts out. I also chucked in an SSD1315 OLED to show the time and a menu to configure it, although there's a web UI as well. The esp32 also means you can fetch the time from NTP.

It also functions as a small heater since I used LDOs to step down 15v to 3.3v for the esp32, I was lazy and didn't use a buck converter circuit :)

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This reminded me of a Blog entry I wrote about in 2013 on "Massive Electro-Pyrotechnic Initiator Chip Resistor (MEPIC)". These are 0805 chip resisters that are by design meant to let out the Magic Smoke that runs all electronic parts.

Sadly I could not get free samples from my Vishay Rep, that I was in good standing with. MEPIC85N8R0KTT come in lots of 10,000 to buy.

Be sure to check out the application note "A Guide to Using EPIC / MEPIC Igniters in Pyrotechnic Applications".

https://www.vishay.com/en/product/53058/

National Semiconductor, bought by TI, used to make a similar part, check out the application note:

https://www.ti.com/lit/an/snoa217/snoa217.pdf

This is what I wrote about the MEPIC parts a long time ago:

"MEPIC resistors, also known as bridge resistors, are resistive elements that convert electrical energy into heat energy in a precise electro-thermal profile for the purpose of initiating a series of pyrotechnic events in a controlled energetic reaction. [They go BOOM on command, which is different than Rapid Spontaneous Self-Disassembly.]

The new Vishay Sfernice resistor is optimized for electronic igniter applications in automotive safety systems for the deployment of airbags and other safety devices; digital blasting in mining applications; and in fireworks applications for better synchronization of fireworks, music, and special effects.

With firing energy down to 1.5 mJ and a typical ohmic range of 2 Ohms (+/- 10 %), the device provides designers with very predictable, reproducible, and reliable behavior.

Offered in the standard 0805 case size for the wraparound and flip chip versions, with other sizes available upon request, the resistor features easy set-up of firing levels, and is compatible with various pyrotechnic compositions.

Offering ESD withstanding to 25 kV without extra protection, the MEPIC resistor's performance meets no fire/all fire conditions and the requirements of USCAR, AKLV16, and major car manufacturer standards.

The device is RoHS-compliant and conforms to Vishay "Green" standards. [Is it not great that Fuzes are 'Green'?]"

MEPIC fuses... ok... Green? Oh my!

You forgot to add a link to the blog :)

It was not an oversight, however since you asked:

http://blog.softwaresafety.net/2013/04/magic-smoke-resistors...

Byte Magazine had an April ad for a Noise Emitting Diode. The symbol was a diode wearing a pair of earmuffs.

I looked that up. Interesting that it appears on page 369. The numbers from the famous N. Tesla quote.

Sadly we've lost such funs stuff in the modern era. Has anything been better than the Signetics Write-Only-Memory from long ago today?

https://dn760104.eu.archive.org/0/items/best_of_byte_volume_...

The actual "make it go bang" bit here isn't the most potent. (I think I have capacitors here which wouldn't care in the least about this, despite their datasheet ratings.)

If you need to take it to the next level, consider something based on a xenon photoflash driver. These aren't as common as they used to be, but they're still not hard to make. I had to make one of these a while back and ended up using one of those $5 LTC chips but that was appropriate for the situation; there are certainly other ways to do it. This will basically charge a 400V capacitor up for you, which you can then dump into the 5V part. High-quality 5V capacitors will handle small spikes of this. But using a big 400V capacitor will make a big spike, which is not kind to the other capacitor. (I must confess I didn't try blowing up a lot of things on the one I made, but it was medical test gear, not technically a capacitor-blower-uper, and I was on deadline anyway. I also had other, significantly more destructive, equipment available to me should that be the goal.)

I expected an alarm clock using a capacitor for timing. Either charge it to a delay-dependent level, or charge it to a fixed level and discharge through a delay-dependent path, or trigger when it drops below a delay-dependent level.

Tangent: I remember when hackaday posts about building cool and or useless circuits were posted constantly to HN. Now I can't remember the last time I saw one. (I know this link isn't hackaday, but it's exactly like what they feature).

Sorry I'm late, the capacitor didn't blow.

Did anyone else smell capacitors when they watched the video? The brain does funny things.

There's a video demonstration about halfway down the GitHub

https://github.com/ArcaEge/capacitor-alarm-clock#Demo

Based. Unhinged. Don't try this at home.

But it is also art. It represents the waste in our devices that play out over 1-4 years (or say a few weeks for a vape) but in one night.

But yeah. Don't do it. Indoors? wtf!!!!

Oh no. I quite liked this until you said it was art that Represented something.

To be brutally honest it sounds like LLM speak to me. The account being in green doesn't help.

The line between an LLM being told to sound like an HN user, and an actual user who's adopted LLM lingo is... vanishingly thin at times. I myself accidentally find myself using such phrases, I can hardly accuse others.

I am human, to prove it I have laid down an em-dash below:

—

For anyone jumping into this thread hoping to see capacitor use for timing, there is this blog post about something like that:

https://notes-huy-rocks.translate.goog/posts/diy-pomodoro-ti...

(google translate link because the original post was in Vietnamese)

That sounds completely safe and healthy! Hmmmm, I love the smell of vaporized electrolyte, particularly when waking up!

I feel like a wire detonator would be safer plus the consumables would be cheaper however even then I doubt vaporized copper or aluminum is good for you. Honestly just roll some firecrackers and use the ESP to light them off.

For some reference work https://www.youtube.com/watch?v=agwKNLoU6g8

But it's got electrolytes!

There are some grades of electrolytic capacitors for which this is probably the only thing they should be used for.

Heh. I hoped to see a fully analog capacitor-based "movement", either a mechanical movement powered by periodic electric pulses, or maybe a device using split-flap displays powered by three highly precise, thermally-compensated capacitor discharge circuits.

Try this with a tantalum capacitor. Careful not to lose an eye...

Luckily our eyes tend to be closed when we're asleep. Evolutionary safety squints.

I'd like to see a study on the threshold of projectiles versus safety squints. I searched around, but couldn't find a paper.

LEDs also work if you've got enough energy to dump into them. Think bulky high-voltage cap + beefy MOSFETs.

So it’s not UL listed?

Do you need the 15V input to torch the capacitors and run the relays? Could I use a 5V USB ESP32 dev board instead, and just put a boost circuit or MOSFET on the relay load side for the explosion circuit when it needs to go off, or are there other components that need the higher voltage?

You could, but from my measurements the capacitor tends to pull ~1A before it bursts, so you'd be running up against the 3A limit of USB. At voltages below 12V, they don't seem to go off reliably.

Have you tried a backwards polarity tantalum capacitor? I've seen those go off just on their normal voltage when installed backwards. Sometimes immediately and other times with significant delay.

Eye Projectile and Eye Flash protection along with hearing protection are required.

What’s happening at the electron level that makes them do this? Anyone know?

If I recall correctly, electrolytic capacitors have to get "burned in" during manufacturing to make them work.

A current is passed through the capacitor and a thin film of oxide is built up in one of the terminals, according to the polarity. This is why electrolytic caps have polarity, if you use them with their polarity inverted, you flake off that oxide layer and thus short them out.

A free running current in that electrolyte boils it off, and you get an exploding cap

The perfect alarm clock would start lighting your life dreams on fire if you didn't wake up, cause that's whats happening anyway.

"A BOM is available under production" - the subtlety is in the spelling... good fun though!

Electroboom did this first, right?

The README references Electroboom's implementation

"Sorry I overslept, the capacitor didn't go off" gonna be funny excuse

Is this not technically an IED?

Doesn't look improvised to me.

This is absolutely how IEDs are made. You buy an old Nokia phone and wire the speaker/ringer to the detonator. Call phone -> boom.

In fact, TFReadme directly references Electroboom/Mehdi Sadaghdar who did this with an old-school analog alarm clock (the kind with an actual bell) and in the video he muses that it's literally a time bomb, har har get it.

> wire the speaker/ringer to the detonator. Call phone -> boom.

Given the constant stream of spam and scam calls I get that seems like an incredibly bad idea.

Wondering if we can adapt this for our pulsed power system :)

the alarm clock for the ai age, it needs an LLM

It is an LLM

a Life limiting machine

Nice job OP, and thanks for the demo video! PS to others, keep your volume below 40%.

...I may or may not have jumpscared myself by cranking the volume up before the alarm time as it was so quiet.

How about a flux capacitor clock?

gng thats crazy!

that's a bomb dude.. lmao.. don't take that anywhere!

Just about anything can be turned into a bomb. Take a coffee cup, a smart watch, and 5 lbs of C4, and it could easily be turned into a bomb, for example.

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