For the last few years, [Lt_Lemming] was the president of Brisbane’s hackerspace. Until several months ago, access to the local was done using 125KHz RFID tags and an Arduino board with a prototyping shield. As the hackerspace gained members and moved to bigger facilities, [Lt_Lemming] decided to build himself a more compact and advanced platform.
His Simple NetworkAble RFID Controller (SNARC) is a platform which can be connected to an Ethernet network and different RFID readers in order to implement smart access control functionalities. Through hole components were selected so even solder apprentices may assemble it. The PCB was designed using Fritzing, and development can even be done inside the Arduino IDE as ISP and serial headers are available on the board. Finally, an N-channel mosfet controls the door locking mechanism.
The project is open hardware and software, and all the sources can be downloaded from [Lt_Lemming]’s github repo.
[Dirk] had a problem: while he already had an Arduino with an Ethernet shield, he needed WiFi for an upcoming project. Running a Cat5 cable was out of the question, and a true Arduino WiFi shield is outrageously expensive. He did, however, have a WiFi router lying around, and decided it would make a perfect WiFi shield with just a little bit of cutting.
The router [Dirk] used was a TL-WR702N, a common router found in the parts bins of makers the world over. Inspiringly, the size of the router’s PCB was just larger than the space between the Arduino’s pin headers. Turning the router into a shield is simply a matter of scoring the edge of the board and gluing on a few pins for mechanical strength.
Power and ground lines were soldered between the pin headers and the router, while data is passed to the Arduino and Ethernet shield through a short cable. It may not look pretty, but if it works in a pinch we can’t complain.
[Angus Gratton] recently cracked open a pair of USB to Ethernet converters to see what’s inside. One was an Apple branded device, the other a no-name from eBay. The former rings in at $30, with the latter just $4. This type of comparison is one of our favorites. It’s especially interesting with Apple products as they are known for solid hardware choices and the knock-offs are equally infamous for shoddy imitations.
From the outside both devices look about the same. The internal differences start right away with a whole-board metal shield on the Apple dongle and none on the off-brand. But the hardware inside is actually quite similar. There’s an RJ-45 jack on the left, followed by the Ethernet isolation chip next to it. From there we start to see differences. The off-brand had a blank chip where Apple’s ASIX AX88772ALF USB to Ethernet bridge controller is located. There is also a difference with the clock; Apple is using two crystals with the other using just one.
[The Backwoods Engineer] tested out a new accessory kit for the STM32-F4 Discovery board. The image above shows two boards communicating with the UDP protocol. Notice the extra PCB into which each Discovery board has been plugged. This is a third-party add-on which adds Ethernet, RS-232, SD card slot, and a connector for LCD or Camera. We’ve had one of these F4 Discovery boards on hand for a while and haven’t figured out a good way to connect external hardware to the huge dual pin-headers. This doesn’t solve the problem — the base board also includes dual headers to break-out all the pins — but having Ethernet, serial, and SD certainly reduces the need to add all that much more. The other drawback to the hardware is that the sample firmware is targeted at the IAR Embedded Workbench which is neither free, nor in the realm of affordable for hobbyists.
The NIC used on the baseboard has auto-crossover capabilities so the boards were connected using a regular Cat6 patch cable. This example has the boards constantly sending UDP packets with the module on the right reporting status information to a terminal via the serial connection.
[Kenneth Finnegan’s] post about this 24-Port HP ProCurve 2824 Ethernet Switch teardown was a delight to read. He’s taking an introduction to networking class at California Polytechnic State University. One of their labs included virtual machines shooting thousands of new MAC addresses at the thing all at once. Despite it’s ability to switch data at a blazing fast rate, it’s ability to deal with that many new hardware identifiers was less than impressive. He wanted to find out why and it just so happened he had one of these in his parts bin at home (which he refers to as if it’s a high-powered RPG character).
The mainboard is divided into three major blocks: the power supply, the switching hardware, and the processor that makes this a manged switch. Although he covers all of these pieces (and the switching stuff is very interesting to learn about) it is the processor section that was causing the aforementioned slowdown. It’s a 266MHz PowerPC chip with a measly 64 MB of RAM. Of course this doesn’t need to be any more powerful since all traffic from previously ‘learned’ MAC addresses gets handled by the switching block and never touches the processor portion.
Don’t miss the end of his post where he discusses how the filtering caps, and semi-isolated ground planes help to tame the beast created from all of this high-speed switching.
[Matt] literally finds himself in a sticky situation. There’s an oil slick in his sump well. These wells work in conjunction with drain tiles to pump water away from the foundation of a house. Unfortunately the tar that was used to waterproof the outside of his foundation is also washing into the sump and gumming up the works. The system he built will sound an audio alarm and send an email if something goes wrong with the sump pump.
He’s monitoring for two different issues. One technique uses a float valve to sense if the water is too high, signalling that the mechanism controlling the pump has malfunctioned. The other is a current monitor that senses if the sump pump has been running too long (caused by the sump’s water sensor getting stuck in the on position). The one thing he didn’t want to do is control the pump directly as a bug in his code will easily result in a flooded basement. We have the same concerns when considering building a DIY thermostat (an error there could mean frozen water pipes leading to flooding).
If you’re lacking useful equipment for your Raspberry Pi hacking adventure, such as an HDMI monitor or power supply, this handy write-up will show you how to continue your hacking. All you’ll need is a laptop, the Raspberry Pi itself, an SD card, and an Ethernet and micro-USB cable. As noted in the article, it’s not really recommended to power the ‘Pi off of USB only, so this could potentially be a source of problems.
This hack begins by installing Linux on an SD card per this setup page, then using a Virtual Network Computing [VNC] setup to work with your Raspberry Pi. There are a few steps in between being able to do this, like setting up network sharing, and sleuthing out the IP address of the new processor, but everything is explained in detail for Mac and Linux. Windows users will have to do a bit of “sleuthing” of their own, but if you have some more information on this process, we’d love to hear about it in the comments!