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DC30: Thinkpad x200 SAO

Sep 19, 2022    #badges   #defcon  

ThinkPad x200 SAO

Are you even a hacker if you don’t do all your hackin’ on a 15 year old IBM thinkpad? These machines are extremely common at Defcon, every fourth person in line is probably holding one by the battery pack, trying to reverse engineer something in Ghidra.

A ThinkPad was an obvious choice for an SAO. I wanted to do something more interesting than just a blinky LED, so I threw a tiny OLED display on it and gave it just enough brains to talk to it.

Designing Around Shortage

The DEF CON these debuted at (DEF CON 30) occurred in the middle of the great parts shortage of the early 2020s. Everyone used an RP2040 on their designs that year, probably because it was literally the only microcontroller you could buy. Unfortunately, that micro is way overpowered for something like this and requires a fair amount of support circuitry (SPI Flash, regulators, lots of caps, etc) to drive properly. What I really wanted was some ATTiny or dead simple PIC micro, but those are entirely unobtainable. Even my shitty, unethical, big tech employer couldn’t get one.

If only someone had a huge stockpile of these, already soldered into some tiny breakout…

Oh yeah, the Digispark! This is a tiny breakout for the ATTiny85. It even has a built in USB interface that they are somehow (seriously how the fuck is this possible) bitbanging out. These boards are super cheap, tiny, and have all the signals broken out for a decent design. They just needed to be through hold soldered onto the SAO

Digispark

Now that we have a micro we can source (Digisparks are in unlimited supply on AliExpress) we just need to throw it onto the SAO with a screen.

Programming

No big tricks here. I used a cool library that manages to drive the OLED with a seriously underpowered micro like this, and did some fancy PROGMEM’ing to get the text into the read only flash portion of memory.

Shitpad Assembly

Assembly

The shortage means these are all through hole components, so they would need to be done by hand, in my room.

The first batch made for DEF CON 30 was HORRIBLY designed for assembly. I managed to somehow get the SAO connector not only backwards, but mirrored too! I thought ahead and added some jumpers to work around this, but I so royally messed up the connector that these were useless. Instead, I ended up wire wrapping the connector to the micro and hot glueing it all in place. Probably the worst bodge job ever, especially since I had to do it 30 times. That really sucked.

Shitpad Rev1

All that is fixed for DEF CON 31. The connector is correct, and I actually got some proper surface mount connectors that I can just reflow on in my oven. Way easier to do this than soldering them all by hand.

Shitpad Rev1

All other components are through hole by necessity. The LED is on the other side of the board so it couldn’t be reflowed in my primitive setup, and my only source of ATTiny85’s is STILL Digispark boards so those also needed to be through hole.

Shitpad Laid Out

Maybe when everything in the world gets fixed and we can order chips again I’ll do a real design that can just be ordered wholesale from china.

Shitpad Testing

All ThinkPad SAOs are assembled, packaged, and tested to make sure they work right. The LEDs are super bright, but sometimes that’s a good thing in the bright Las Vegas sun.



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dcpunks / PawprintPrototyping / notgood.link / pinball! / elf / kebo / dcpunks / stinky / alex lynd /