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PCB devboard the size of a USB-C plug

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Re: PCB devboard the size of a USB-C plug

#21

Post by throwup238 »

jasongill wrote: post #16
rkagerer wrote: post #13

Earlier quoted context omitted.

That's it, I'm going back to parallel port cables for everything now.

The parallel port (at least in it's later implementations) actually supports DMA - I'm sure that data exfiltration via the parallel port is hard, but probably not impossible... Nothing is safe, unfortunately!

It’s almost certainly impossible on modern systems. The southbridge which allowed DMA to parallel port was absorbed into PCH and slowly stripped of legacy LCP support by chipset and motherboard manufacturers.

Re: PCB devboard the size of a USB-C plug

#22

Post by claytongulick »

rkagerer wrote: post #4
chrisallick wrote: post #2

This looks awesome, I'd love to get one. Question, what's the advantage over something like the ESP32C3 and the like? Just even smaller?

If it helps, I've used earlier Atmel AVR chips, as well as the ESP32-S3. 8-bit AVR is an extremely clean, relatively simple instruction set that can be viably hand-coded. It's fairly straightforward to calculate the exact number of cycles your code will use, which is handy for applications requiring deterministic timing and for knowing worst-case execution time of interrupt handlers. If the C3 instruction set is anyt…

I'll second this.

Doing asm on the AVR is beautiful, you can count clock cycles easily and then observe them on the scope.

I wrote a bit banging serial interface for an AVR once and had a mystery when I was testing it from a PC just with a basic echo. Every Nth character would be wrong. Was able to figure out a timing problem by counting clock cycles and found the bug in my code.

Was cool to see it align with what I was seeing on my oscilloscope.

Re: PCB devboard the size of a USB-C plug

#25

Post by sleepydog »

tl2do wrote: post #5

I'm interested in this too. I've been using STM32 NUCLEO boards, which are cheap and capable, but even the smallest ones are noticeably larger than this. I'd love to see an STM32 version of this project.

https://tomu.im/somu.html

This is an stm32l432kc in the form of a yubikey nano.

Re: PCB devboard the size of a USB-C plug

#28

Post by gucci-on-fleek »

d0able wrote: post #26

Very cool, but what about the $ to manufacture? Things get exponentially(?) harder the smaller it is, especially for custom boards.

Looks like it only has 6 discrete components [0], and the pinout on the MCU looks like a standard QFP [1] (and everything else is on larger pads), so I think that you should be able to manufacture this using standard production techniques/manufacturers. But I know hardly anything about hardware, so I may be completely wrong here.

[0]: https://github.com/user-attachments/assets/0f7962d5-38e1-4bd...

[1]: https://en.wikipedia.org/wiki/Quad_flat_package

Re: PCB devboard the size of a USB-C plug

#30

Post by FiniteIntegral »

d0able wrote: post #26

Very cool, but what about the $ to manufacture? Things get exponentially(?) harder the smaller it is, especially for custom boards.

It's not that things get more expensive as they get smaller. As long as you're within reasonable tolerances it can be more cost effective. There is very little reason in a consumer-grade product, especially a devboard, to push any major fabs' tolerances. SMD components are grain-sized and you can make traces pretty thin.

For example, this project is a 2-layer PCB. Those are bog standard. With this small of a footprint it can be printed on a single surface and cut out. The schematic they posted keeps everything on a single surface for print. This is also an operation any fab can easily perform. If you order from China, even cheaper (even accounting for duty cost + S&H).

I'd be more concerned about the MCU and the components rather than the cost of a custom PCB.

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