Wireless Hacks

1078 Articles

Wireless Power Transfer Using Capacitive Plates

July 17, 2015 by 33 Comments

It seems like wireless power transfer is all the rage these days. There’s wireless charging mats, special battery packs, heck, even some phones have it built in! And they all use inductive coils to transfer the power — but what if there was another way? Coils of copper wire aren’t always that easy to fit inside of a product…

As an experiment, [Josh Levine] decided to try making a proof of concept for capacitive power transfer.

He first demonstrates inductive power transfer using two coils of copper wire to power up an LED. The charging coil is supplied with 15V peak-to-peak at 1MHz which is a fairly typical value for inductive charging. He then shows us two glass plates with some tinfoil taped to it. Two LEDs bridge the gap alternating polarity — since the power is oscillating, so we need a path for electrons to flow in both directions. There is no connection through the glass, but when it is set on the charging plate, the LEDs light up. The charging plate is supplied with 30V peak-to-peak at 5MHz.

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Transmitting MIDI Signals With XBEE

July 17, 2015 by 27 Comments

What do you do when you want to rock out on your keytar without the constraints of cables and wires? You make your own wireless keytar of course! In order to get the job done, [kr1st0f] built a logic translator circuit. This allows him to transmit MIDI signals directly from a MIDI keyboard to a remote system using XBEE.

[kr1st0f] started with a MIDI keyboard that had the old style MIDI interface with a 5 pin DIN connector. Many new keyboards only have a USB interface, and that would have complicated things. The main circuit uses an optoisolator and a logic converter to get the job done. The MIDI signals are converted from the standard 5V logic to 3.3V in order to work with the XBEE.

The XBEE itself also needed to be configured in order for this circuit to work properly. MIDI signals operate at a rate of 31,250 bits per second. The XBEE, on the other hand, works by default at 9,600 bps. [kr1st0f] first had to reconfigure the XBEE to run at the MIDI bit rate. He did this by connecting to the XBEE over a Serial interface and using a series of AT commands. He also had to configure proper ID numbers into the XBEE modules. When all is said and done, his new transmitter circuit can transmit the MIDI signals wirelessly to a receiver circuit which is hooked up to a computer.

DNS Tunneling With An ESP8266

July 1, 2015 by 51 Comments

There’s a big problem with the Internet of Things. Everything’s just fine if your Things are happy to sit around your living room all day, where the WiFi gets four bars. But what does your poor Thing do when it wants to go out and get a coffee and it runs into a for-pay hotspot?

[Yakamo]’s solution is for your Thing to do the same thing you would: tunnel your data through DNS requests. It’s by no means a new idea, but the combination of DNS tunneling and IoT devices stands to be as great as peanut butter and chocolate.

DNS tunneling, in short, relies on you setting up your own DNS server with a dedicated subdomain and software that will handle generic data instead of information about IP addresses. You, or your Thing, send data encoded in “domain names” for it to look up, and the server passes data back to you in the response.

DNS tunneling is relatively slow because all data must be shoe-horned into “domain names” that can’t be too long. But it’s just right for your Thing to send its data reports back home while it’s out on its adventure.

Oh yeah. DNS tunneling may violate the terms and conditions of whatever hotspot is being accessed. Your Thing may want to consult its lawyer before trying this out in the world.

Wireless Weather Station

June 22, 2015 by 12 Comments

High schooler [Vlad] spent about a year building up his battery-operated, wireless weather station. Along the way, not only has he learnt a lot and picked up useful skills, but also managed to blog his progress.

The station measures temperature, humidity, pressure and battery voltage, and he plans to add sensors for wind speed, wind direction and rainfall soon. It is powered via a solar panel and can run on a charged battery for a full month. The sensor module transmits data to a remote receiver connected to a computer from where it is published to the internet. Barometric pressure is measured using the BMP180 and the DHT22 provides temperature and humidity values. The link between the transmit and receive sections uses a 433MHz Superhetrodyne RF Kit which gives [Vlad] a range of 50m. There’s an ATMega328 on the transmitter and receiver side. He’s taking measurements once every 12 minutes, and putting the micro controller in low power mode using the Rocket Scream Low Power Library. A 5W, 12V solar panel charges the 6V Lead Acid battery via a LM317 based charge circuit. This ensures the battery gets charged even when the solar panel is not receiving optimal radiation. One hour of sunlight provides enough charge to keep it going for 2 days. And a fully charged battery will keep it running for a full month even when there’s no sunlight.

The server software consists of two parts. The first pushes serial data to a mySQL database. This is written in Visual Studio C# using help from Oracle mySQL connector. The second part publishes the entries in the mySQL database to the web server. This is written in php, and uses  Libchart for graphing. He’s got the code, schematics, parts list and a lot of other information available for download on his blog. There’s a couple of items pending on his to-do list, so if you have any tips to offer post your comments below.

IR Remote For Smartphone Via Bluetooth Adapter

June 19, 2015 by 8 Comments

Quite often, the raison d’être for building a project is to learn and hone one’s skills. In which case it doesn’t matter if the end use seems a bit frivolous. [indiantinker] built BlueIR, a device to control Bluetooth A2DP devices using an archaic IR Remote using a BT-Aux Adapter.

Sounds convoluted? Let’s try again. He uses an old IR remote to send data to a MSP430-series  microcontroller, which is connected over serial to a USB Bluetooth Receiver Adapter, which in turn is connected to a set of wired speakers. The Bluetooth adapter is paired with his phone. The IR remote allows him to control the audio player commands on his phone from a far greater distance compared to the bluetooth adapter.

He begins by breaking open the BT adapter to find that the markings on the chip have been erased. What he did find instead, were two pads promisingly marked as TX and RX, but he still did not know the baud rate or the command set. Digging around the Internet, he figured out that the chip used was the OVC3860 Bluetooth 2.0 + EDR Stereo Audio Processor and found its list of AT Commands. After some tests using a serial console he figured out that it worked at 115600 baud. Soon enough, he had it hooked up to the MSP430 Launchpad and was able to communicate. Next up, he built a small PCB, using the toner transfer method. The board consists of the MSP430G2553 micro controller, IR receiver, LED, some decoupling capacitors and a few pull up resistors. He leached power from the 3.3V regulator on the host BT adapter. The assembled PCB is piggy backed on top of the BT adapter for the time being, and a 3d printed housing is on his to-do list. His code is available at the BlueIR Github repo and the video below shows it in action.

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Tracking Bitcoin With The ESP8266

June 18, 2015 by 15 Comments

[Kendrick] was looking for something to do with an ESP8266 WiFi module, and since he loves Bitcoin and Arduino, the obvious solution was to make a Bitcoin price tracker.

The ESP8266 is a complete microcontroller with a WiFi chip and a few pins for a serial connection. It’s certainly possible to write some firmware for the ESP to get the current conversion rate of Bitcoin, but for simplicity’s sake, [Kendrick] chose to use an Arduino for this project. He’s using a 5V Arduino, and the ESP operates on 3.3V logic, but a few Zeners take care of the logic level conversion.

The code running on the Arduino checks the CoinDesk API minute, parses the JSON coming from the API, and prints the current Bitcoin price to the serial port. For tracking the current conversion rate of Bitcoin, it’s vastly overkill. This project could have a few interesting applications, from hooking up a few seven-segment displays, to an RGB LED mood lamp that keeps track of this magic Internet money.

Wifibroadcast Makes WiFi FPV Video More Like Analog

June 13, 2015 by 23 Comments

Normal WiFi is not what you want to send video from your quadcopter back to the first-person-view (FPV) goggles strapped on your head, because it’s designed for 100% correct, two-way transmission of data between just two radios. Transmission of analog video signals, on the other hand, is lossy, one-way, and one-to-many, which is why the longer-range FPV flights all tend to use old-school analog video transmission.

When you’re near the edge of your radios’ range, you care much more about getting any image in a timely fashion than about getting the entire video sequence correctly after a delay. While WiFi is retransmitting packets and your video is buffering, your quadcopter is crashing, and you don’t need every video frame to be perfect in order to get an idea of how to save it. And finally, it’s just a lot easier to optimize both ends of a one-way transmission system than it is to build antennas that must receive and transmit symmetrically.

And that’s why [Befinitiv] wrote wifibroadcast: to give his WiFi FPV video system some of the virtues of analog broadcast.

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