Show HN: F32 – An Extremely Small ESP32 Board
257 points
1 day ago
| 13 comments
| github.com
| HN
As part of a little research and also some fun I decided to try my hand at seeing how small of an ESP32 board I can make with functioning WiFi.
jacquesm
17 hours ago
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If you add another GPIO and make a silicone mold you could make an in-cable eavesdropper on USB connections that streams out the data via the wifi. That would be a pretty scary tool in the right circumstances.
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atemerev
17 hours ago
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These cables can be bought for like $200 mostly legally.
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tmpfs
1 day ago
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This is a very cool experiment, even if the board doesn't end up being that practical (the antenna hack is going to be an ongoing issue I think) your documentation looks great at a glance!
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pegor
1 day ago
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Thank you! I agree, antenna definitely needs some improvement.
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wkat4242
3 hours ago
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You should take the metal of the USB connector into account. This will significantly alter the emission pattern of the antenna. Try to find a radio amateur in your area, we have equipment to measure and software to predict antennas.
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wkat4242
3 hours ago
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People that hide exploit devices in public chargers are going to love this one lol. Cheap, small and enough power
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actinium226
10 hours ago
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Neat! I just sent out an order to JLCPCB for an ESP32 based board. I don't have a rework station or any experience with SMT so I decided to go for their assembly options. It's 80 per board, but would probably be cheaper per board if I got more than 2 (I also have more components on my board than you).

Question about the instructions in your README, you say that once you're done with the top side, repeat for the bottom, but when you're working on the bottom side, what stops the elements on the top side from falling off once the heat passes through the board and melts the solder on that side?

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pegor
7 hours ago
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Working on the bottom side I only used the heat gun really carefully on the resistors then used a soldering iron with a fine tip for the usb-c connector since the leads are fairly large.
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4b11b4
7 hours ago
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Surface tension of solder in liquid state can hold the parts while upside down. Depends on weight of component & geometry of pads
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brokenmachine
8 hours ago
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"Bottom side must be done using a rework hot air gun, not possible with hotplate."

Basically you're hoping the bottom side doesn't get hot enough for everything to move or fall off.

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Rebelgecko
15 hours ago
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Really cool. I just ran into a situation where it would be handy to have a small Bluetooth device that plugs into USB-C. However soldering something like this seems a bit beyond me, is there a more turnkey solution?
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dotancohen
12 hours ago
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The company that printed the PCB, PCBWay, also offers PCBAs. They're really not expensive, though you might need to order in batches of multiples of five.
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actinium226
10 hours ago
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JLCPCB also offers assembly and they're much, much cheaper, like an order of magnitude cheaper.
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wkat4242
3 hours ago
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Wow thanks!!! I've been trying to find a cheap flex pcb supplier but the cheapest i found was $150 for 10. They are way cheaper making my project viable!
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stavros
13 hours ago
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This is great, well done! I don't know where I'd use this, but I'd definitely want to use it.
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anyg
1 day ago
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If it is a little bigger to incorporate a bigger chip antenna and some GPIO pins, it is going to be very useful for a lot of IoT projects!!
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margalabargala
17 hours ago
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The XIAO series of ESP32s is exactly that.

They are 4x the size though, almost exactly double in both length and width.

https://wiki.seeedstudio.com/XIAO_ESP32C3_Getting_Started/

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dotancohen
12 hours ago
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It's also got 15 times as many GPIO pins as the board in the fine article.

And this PCBA will be smaller than the battery in most applications anyway.

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margalabargala
12 hours ago
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It only has 14 pins, 3 of which are 5v, 3.3v, and ground, so slight exaggeration :-) point taken though
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sho_hn
13 hours ago
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These are quite lovely. Ceramic SMD antennas are awesome.
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pegor
19 hours ago
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Definitely would be more functional with more of the GPIOs exposed.
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forsalebypwner
17 hours ago
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If you want an ESP32 dev board with GPIOs exposed there are dozens (or hundreds, maybe thousands) of other options out there. It makes sense not to expose them when you're going for the smallest possible footprint.
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stavros
4 hours ago
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I don't know, I see enough space for four GPIOs there. Not holes, obviously, but pads should be very workable.
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imtringued
3 hours ago
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It could be even smaller without that USB C port and have more GPIO pads.
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PunchyHamster
18 hours ago
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there is plenty of those already and not all too hard to make yourself, see LilyGo T01-C3

Its of format of original ESP8 so you get serial + 3 IO pins

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Swannie
11 hours ago
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I was thinking "how much smaller than the cheap 30mm x 25mm boards on AliE can you go?" ... much smaller!

Very nice.

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selcuka
6 hours ago
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FYI XIAOs are 21x18mm.
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k__
1 hour ago
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I just learned about XIAO boards from Grok a few days ago, lol.

The Sense versions are pretty rad. Now I only have to add a battery and a touch sensor and I'm good to go.

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allenrb
12 hours ago
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Jesus. You had me at “hand-soldered 01005 components”.

I’m tempted to try a few of these just to see how disastrous my build efforts are.

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ingen0s
17 hours ago
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Nice work, kudos!
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Gys
16 hours ago
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> PCBWay does also offer assembly services

Seriously? For a tiny board like this also? Genuine question.

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kube-system
16 hours ago
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yes, but they use a machine, they don't do it by hand.
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puzzlingcaptcha
15 hours ago
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01005? Oh no no no. I can barely do 0402s by hand and those are _2.5x_ larger.
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joemi
12 hours ago
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Wouldn't 0402 be 4x larger (if comparing lengths) or 16x larger (if comparing areas), not 2.5x?

Edit: Nevermind, I was wrong. I see now that the sizes don't actually directly correspond to the number codes! 01005 is 0.4mm x 0.2mm and 0402 is 1mm x 0.5mm. That's annoyingly confusing, IMO.

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Neywiny
8 hours ago
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Metric mm vs imperial thou. Confusing but at least explainable
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sho_hn
15 hours ago
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With one of those mini-hotplates for reflow soldering and a LCD microscope it's still fairly doable.
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VTimofeenko
15 hours ago
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FWIW, there's a step by step soldering guide in the readme:

https://github.com/PegorK/f32#building-the-f32

It looks doable, but of course a lot of carefulling is required when placing the components.

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numpad0
11 hours ago
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infuriating fact: 0402 metric = 01005 imperial, 0402 imperial = 1005 metric. looks like this is the only semi-duplicate in common use.
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rts_cts
10 hours ago
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And that's how I ended up with half a reel of 01005 resistors...
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stavros
4 hours ago
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Wait wait wait what? 01005 isn't metric? They switched to imperial for just that size? What?
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numpad0
1 hour ago
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I was a bit outdated with resistor sizing and I don't have a great sources but apparently there are:

    inch 0402, 0201, 01005, 009005, 008004, $1
    mm   1005, 0603, 0402,  03015,  0201,   01005
these sizes... and $1 is the one in your mind that shall not be written in inches. The "01005 imperial" is just 0402, so it's not going up to the metric 01005 scale or beyond. I think.
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NuclearPM
1 day ago
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> This can be seen in my highly necessary depiction below.

I love this. Fun and insightful article. Thank you.

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unwind
4 hours ago
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Me too, but that particular picture was confusing. Shouldn't the board be with the human, 120 ft from the wifi access point being connected to? Now it looks as if the human screams at the board from 120 ft away, or something.

Other than that, hugely impressive project of course, it makes any board I've tried to design/assemble look impossibly huge. :)

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pegor
19 hours ago
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Thanks for checking it out!
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