The Development Of A Lightweight Wireless Protocol

June 12, 2014 by Brian Benchoff 30 Comments

BANO [Texane] had been thinking about how to monitor the state of his garage door from a remote place. The door itself isn’t around any power outlets, and is a few floors away from where his server would be located in his apartment. This presented a few design challenges – namely, the sensor itself should have a wireless connection to the server, and being low power would be a great idea. This led to the development of a minimalist framework for wireless communication that allows a sensor to run for weeks without a battery swap.

The wireless protocol itself is based on a simple key value pair; each individual sensor, coupled with a NRF905 radio, has passes an address, a key, and a value. There are allowances for checksums and acknowledgement, but as the PDF says, this is a very minimal protocol.

With the software out of the way, [Texane] turned to the hardware. The microcontroller is a simple Arduino clone, paired with a radio and a coin cell on a small board. The micro spends most of its time in a low power state, with the sensor, in this case a reed switch, tied to an interrupt pin.

There was a problem with the power consumption of the radio, though: when the short 17-byte message was transmitting, there was a significant voltage drop. This was okay with a fully charged battery, but with a partially drained coin cell, the possibility of brownouts was high. A big cap in parallel was enough to offset this voltage drop.

It’s still a little expensive for an all-in-one home automation and monitoring system, but developing a functional wireless protocol and the hardware to go with it is no small feat. It’s actually a great piece of kit that [Texane] is sure to find a few uses for.

Stuff Wireless Charging Into A Nook’s Crannies

June 10, 2014 by Kristina Panos 21 Comments

Qi receiver for Nook Many technologies that come about for one type of product make us want to extend it to other things. For instance, we’d like the ability to remotely unlock our front door when it’s raining or our hands are full. Once [MS3FGX] experienced Qi wireless charging with his Nexus 5, he wanted the ability to wirelessly charge all the things. The first gadget on the list was his Nook Simple Touch eReader, which he successfully retrofit with a Qi receiver.

Space is at a premium inside of most modern technology. As it turns out, there is a burgeoning market for shoving inductive charging receivers into things. [MS3FGX] decided to try a Qi receiver meant for a Samsung S3, and it actually fits very well behind the battery. He glued it down and then cut a channel in the battery tray for the wires.

[MS3FGX] went full hack with this one and wired it to the Nook’s USB port on the inside. He would have preferred a thinner wire, but used some from a 40-pin IDE cable with little trouble. After the operation was complete, he put it on the Qi pad and it started charging right away. To his delight, the battery increased 20% after an hour. And yes, he can still charge the Nook the traditional way without any issues.

If you want to add wireless charging to any phone cheaply and easily, we’ve got you covered.

A Tweeting Litter Box

June 6, 2014 by Nick Conn 44 Comments

SmartLitterBox

How can you not be interested in a project that uses load cells, Bluetooth, a Raspberry Pi, and Twitter. Even for those of our readers without a cat, [Scott’s] tweeting litter box is worth the read.

Each aspect of this project can be re-purposed for almost any application. The inexpensive load cells, which available from eBay and other retailers, is used to sense when a cat is inside the litter box. Typically sensors like the load cell (that contain a strain gauge) this use a Wheatstone bridge, which is very important for maximizing the sensitivity of resistive sensor. The output then goes to a HX711, which is an ADC specifically built for load cells. A simple alternative would be using an instrumentation amplifier and the built-in ADC of the Arduino. Now, the magic happens. The weight reading is transmitted via an HC-06 Bluetooth module to a Raspberry Pi. Using a simple Perl script, the excreted weight, duration, and the cat’s resulting body weight is then tweeted!

Very nice work! This is a well thought out project that we could see being expanded to recognize the difference between multiple cats (or any other animal that goes inside).

PirateBox, For All Your Wireless Dead Drop Needs

May 31, 2014 by Brian Benchoff 13 Comments

piratebox

Here’s an interesting idea: get a router, Android device, or Raspberry Pi, put it on its own wireless network, and allow anyone to upload and download files. That’s a PirateBox, a small node in the web of digital culture and also a really great way to distribute files at a LAN party.

We’ve seen these type of things before, but now, thanks to [David] and [Matthias], and a bunch of other people, there’s now an easy way to turn a Raspi, Android, or anything that runs OpenWrt into a wireless dead drop. Also included in the software is an image board (think chan) a chat room, UPnP media server, and a browser-based file sharing system. Want to share a “linux distro”? Just upload it to the box over WiFi and it’s available to anyone in range.

Installers are available for devices you probably have sitting around in a junk drawer. Great for that Pi you’re trying to find a use for, and figuring out how to run one of these completely off the grid is an interesting challenge, to boot.

The I2C Programmable NFC Tag

May 30, 2014 by Brian Benchoff 22 Comments

NFC NFC tags are cool, but programming them to do your bidding – whether unlocking your computer, making an Arduino vending machine, or a smart home application – requires using an NFC device to program the tag over the air. An NFC tag programmable with any ‘ol microcontroller would certainly have some interesting applications, and Elecfreaks’ DNFC tag is just the thing to test out these ideas.

While NFC tags are reprogrammable, reprogramming them requires an NFC controller, be that through a dedicated hardware, a phone, or an Arduino shield. The DNFC tag is reprogrammable with a microcontroller with an I2C interface thanks to TI’s RF430CL330H dynamic NFC transponder IC. It still does everything you would expect from a NFC tag – MIFARE compatible. NDEF reading and writing, and everything else – but you can program it through an Arduino, Pi, or any other board with an I2C interface.

TI has an app note on using the chip inside the DNFC for automatic Bluetooth pairing, and Elecfreaks themselves have a few use cases in mind that include putting WiFi credentials on an Arduino board without putting the SSID in code and other Internet of Things™ applications. We’re thinking this is one of those devices that is eminently useful, but for something we just can’t think of off the top of your head. If you’ve got an idea for how to use an I2C programmable NFC tag, drop a note in the comments.

Elecfreaks is doing an Indiegogo campaign for the DNFC, $13 for one. I picked one up, but it’s flexible funding, so buy it or don’t. I don’t care.

A Wireless Computer Remote That Emulates A USB Keyboard

May 25, 2014 by Nick Conn 7 Comments

PCRemote

If you are anything like [Antoine], you would love to be able to control your PC with a simple hand-held remote control from anywhere in your house. [Antoine] wrote in to tell us about his wireless computer remote that emulates a USB keyboard, making it suitable for any device that uses a USB keyboard.

His blog post is very well written and contains a ton of design information and background on the project. He initially wanting to easily control his PC’s music from anywhere in his house without needing to be within line of sight of his computer. The end result is a very handy remote that can be used to change music, video, and even launch applications on his computer. The system consists of a base station for his remote that connects to the computer and acts as a USB keyboard, and the remote itself. The base station uses V-USB on an Arduino to interface with the computer, and VirtualWire to handle the wireless protocol for the remote. For those of you who don’t know about VirtualWire (now superseded by RadioHead), it is a very cool Arduino library that lets you easily use raw wireless interfaces (also called vanilla wireless interfaces).

Without going into too much detail here (be sure to see the actual post for more information), the remote itself was redesigned after the initial proof of concept to maximize battery life. The final power consumption is very impressive, resulting in a battery life of more than two years! This remote system is very well put together and contains many aspects that can easily be reused for other projects.

Firmware For Cheap Bluetooth Modules

May 18, 2014 by Brian Benchoff 43 Comments

If you’ve ever built anything with a microcontroller, some sort of sensor, and a connection to the outside world, you’re probably wondering how those places in China can pump out cheap electronics for a mere percentage of what it costs you to pull a DIY. It’s not just volume – it’s engineering; if something has Bluetooth, you find a Bluetooth module with a built-in microcontroller so you can write firmware to it.

The BC417 is the System on Chip found in the very popular BlueCore4-Ext Bluetooth module featuring 8Mbits of Flash (75% of which is used for Bluetooth related stuff), somewhere around 12 kB of RAM, with everything run in a virtual machine. [pfalcon] wrote an extremely experimental firmware for this device that allows anyone to create a wireless sensor node for peanuts. These devices are almost as cheap as a bare ATMega, so the possibilities are interesting, to say the least.

At this point, the hardest part of putting custom firmware on these devices is programming them. For that, [Elastic Sheep] comes to the rescue with a parallel port to SPI interface. There’s also a firmware dumper and some breakout boards available. These modules are pretty cheap, and the pitch isn’t too bad, so you might be able to etch your own boards should you want to experiment a little.

Thanks [Peter] for sending this in.