Designing An RF Transceiver

December 9, 2010 by Mike Szczys 15 Comments

[William Dillon] is finishing up his degree. His final project as a student was to design an RF transceiver. He decided to work with the Microchip MRF49XA, which runs around $3 but will cost you $20 if you want it in a ready-to-use module. He didn’t find a lot of info on the Internet about communicating with these chips so he’s shared his design, code, and board files. If you’re ever wanted to delve into RF design this is a good primer. [William] talks about building around the example circuit from the datasheet but also includes a discussion of the calculations he made in working with the 434 MHz band, and an AVR-based library for using his module.

Home Automation Without Pulling Wires

November 9, 2010 by Mike Szczys 14 Comments

Here’s a bit of simple home automation using hacks with which we’re become pretty familiar. [Mrx23] combined OpenWRT, a microcontroller, and a set of RF controlled outlet switches to add automation to his plug-in devices. An RF remote that controls the switched outlets has been connected to an Arduino. The router communicates with the Arduino via a serial connection. And the router is controlled by a web interface which means you can use a smartphone or other web device to control the outlets.

The best thing about this system is the power that the router wields. Since it has an underlying Linux kernel you have the option of setting CRON jobs to turn lighting on and off, and group settings can be established to set up a room’s lighting level for watching movies, hosting guests, etc. Combine this with the fact that OpenWRT can use port forwarding for Internet control and the possibilities really start to open up.

[Thanks Arpad]

FM Bug Using Salvaged SMD Parts

October 22, 2010 by Mike Szczys 20 Comments

If you’re a soldering ninja this FM transmitter bug is for you. It’s quite similar to the one we looked at yesterday, but this uses 100% salvaged parts. Two phones donated components; a Nokia 3210 for its voltage-controlled oscillator and a Nokia 1611 for the rest of the parts. The bad news is that mobile technology like cellphones use some of the smallest surface mount packages known to man. That’s where the soldering skill come into play. The good news is that if you’ve been scavenging for discarded phones in order to reuse their LCD screens you already have these parts on hand.

[Thanks George]

Data Confirmation With RF Communications

October 18, 2010 by Mike Szczys 35 Comments

[Rafael] built a system that uses radio frequency for communications. The code he was using with the inexpensive receiver/transmitter pairs already had some error correction but from time to time an entire message would be missed by the receiver. He set out to make these RF communications more robust.

A little more than a year ago we looked at using these same transmitters with an Arduino. [Rafael] has a similar setup but since they are unidirectional he chose to use two pairs for bidirectional communication (each operating at a different frequency to avoid interference). On one end, a computer transmits data to the Arduino which is in a remote location. His confirmation protocol relies on a randomly generated message identifier. The computer will continually transmit the same message. The Arduino continually receives these messages, comparing them with the last successfully received message. If they match, it is considered a successful data transfer and the Arduino transmits a confirmation back to the computer which then starts transmitting the next message.

This isn’t an application-specific protocol. For demonstration purposes [Rafael] built a quick home automation setup that uses it to operate a house lamp.

Giving An IR Transmitter Some Strength

August 22, 2010 by Mike Szczys 17 Comments

[Jkx] was using a Thomson VS360U video transmitter to make a wireless connection between a cable box and his television. The system using an RF remote, but relies on an IR transmitter to communicate between the base station and the cable box. He found the IR module that comes with the device is under-powered and set out to fix the situation. Using a scope he found the pin that drives the IR LED. The board above contains a boost circuit that patches into voltage and ground, using the pin he sniffed out to control the base of a transistor. Now the device has enough power to reliably control the cable box.

Wireless Garage Door Indicator

July 5, 2010 by Mike Szczys 13 Comments

[Sixerdoodle’s] garage door indicator tells him if the door is open or closed. He was inspired by the hack from last September but wanted to make it wireless. The setup uses an RF transmitter/receiver pair from Sparkfun, each controlled by an ATtiny13 microcontroller. We found his battle with RF interference from other devices to be interesting. Working out those bugs made for a great learning experience.

Reverse Engineering An RF Clicker

July 5, 2010 by Caleb Kraft 17 Comments

[Travis Goodspeed] has pulled apart a TurningPoint response card, which is an RF device for answering quizzes, attendance checks, and casting votes in a classroom setting. After tearing it apart, he set out to reverse engineer it and managed to get quite a lot done. At this point he can spoof cards, so he could fake his or several people’s attendance. He can also sniff the packets as they are sent, opening up a plethora of opportunities to mischief. The one that was mentioned in the tip line was to simply repeat the answer that was most often sent for the quizzes. The writeup is very detailed and has great pictures. Good job [Travis].

[thanks Springuin]