Dissecting The TL-WR841N For Fun And Profit

The TP-Link TL-WR841N isn’t a particularly impressive piece of hardware, but since it works decently well and sells for under $20 USD, it’s one of the most popular consumer routers on Amazon. Now, thanks to [TrendyTofu] of the Zero Day Initiative, we now have a concise step-by-step guide on how to hack your way into the newer versions of the hardware and take full control over this bargain WiFi device. This work was initially done to help test out reported vulnerabilities in the router’s firmware, but we’re sure the readers of Hackaday can come up with all sorts of potential uses for this information.

TP-Link helpfully labeled the UART pins

The story starts, as so many before it have, with a serial port. Finding the UART pads on the PCB and wiring up a level shifter was no problem, but [TrendyTofu] found it was only working one-way. Some troubleshooting and an oscilloscope later, the culprit was found to be a 1kΩ pull down resistor connected to the RX line that was keeping the voltage from peaking high enough to be recognized.

Once two-way communication was established, proper poking around inside the router’s Linux operating system could begin. It wasn’t a huge surprise to find the kernel was ancient (version 2.6.36, from 2010) and that the system utilities had been stripped to the absolute bare minimum to save space. Replacing the firmware entirely would of course be ideal, but unfortunately OpenWRT has dropped support for the newer hardware revisions of the TL-WR841N.

To teach this barebones build of Linux some new tricks, [TrendyTofu] used the mount command to find a partition on the system that actually had write-access, and used that to stash a pre-compiled build of BusyBox for MIPS. With a more complete set of tools, the real fun could begin: using GDB to debug TP-Link’s binaries and look for chinks in the armor. But feel free to insert your own brand of mayhem here.

You might think that in the era of the Raspberry Pi, abusing cheap routers to turn them into general purpose Linux boxes would be somewhat out of style. Frankly, you’d be right. But while the days of strapping Linksys WRT54Gs to remote controlled cars might be long be gone, there are still some routers out there interesting enough to make it worth dusting off this time-honored hardware hacker tradition.

Smoothieboard Gets An Ambitious Update For V2

If you’ve been reading Hackaday for awhile, there’s an excellent chance you’ve seen a project or two powered by the Smoothieboard. The open source controller took Kickstarter by storm in 2013, promising to be the last word in CNC thanks to its powerful 32-bit ARM processor. Since then we’ve seen it put to use in not only the obvious applications like 3D printers and laser cutters, but also for robotic arms and pick-and-place machines. If it moves, there’s a good chance you can control it with the Smoothieboard.

But after six years on the market, the team behind this motion control powerhouse has decided it’s time to freshen things up. The Kickstarter for the Smoothieboard v2 has recently gone live and, perhaps unsurprisingly, already blown past its funding goal. Rather than simply delivering an upgraded Smoothieboard, the team has also put together a couple “spin-offs” targeting different use cases. If Smoothie v1 was King of CNC boards, then v2 is aiming to be the Royal Family.

Smoothieboard v2-Prime with breakouts

The direct successor to the original board is called v2-Prime, and it’s everything you’d expect in an update like this. Faster processor, more RAM, more flash, and improved stepper drivers. There’s also available GPIO expansion ports to connect various breakout boards, and even a header for you to plug in a Raspberry Pi. If you’re looking to upgrade your existing Smoothieboard machines to the latest and greatest, the Prime is probably what you’re after.

Then there’s the v2-Mini, designed to be as inexpensive as possible while still delivering on the Smoothieboard experience. The Mini has the same basic hardware specs as the Prime, but uses lower-end stepper drivers and deletes some of the protection features found on the more expensive model. For a basic 3D printer or laser cutter, the Mini and its projected $80 price point will be a very compelling option.

In the other extreme we have the v2-Pro, which is intended to be an experimenter’s dream come true. It features more stepper drivers, expansion ports, and even an integrated FPGA. Realistically, this board probably won’t be nearly as popular as the other two versions, but the fact that they’ve even produced it shows how committed the team is to pushing the envelope of open source motion control.

Our coverage of the original Smoothieboard campaign back in 2013 saw some very strong community response, with comments ranging from excited to dismissive. Six years later, we think the team behind the Smoothieboard has earned a position of respect among hackers, and we’re very excited to see where this next generation of hardware leads.

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