[Dave Jones] from EEVBlog.com takes “Arduino fan boys” off the garden path getting down and dirty with different methods to capture, evaluate and retransmit IR remote control codes. Capturing and reproducing IR remote control codes is nothing new, however, [Dave] carves his own roads and steers us around some “traps for young players” along the way.
[Dave] needed a countdown timer that could remotely start and stop recording on his Cannon video camera, which he did with simplicity in a previous EEVBlog post using a commercial learning remote control unit. The fans demanded better so he delivered with this excellent tutorial capturing IR codes on his oscilloscope from an IR decoder (yellow trace) as well as using an IR photo transistor (blue trace) which showed the code inclusive of 38 KHz carrier frequency. Either capture method could easily be used to examine the transmitted code. The second lesson learned from the captured waveforms was the type of code modulation being used. [Dave’s] remote transmitted NEC (Japanese) pulse length encoding — which can be assertaind by referencing the Infrared Remote Control Techniques (PDF). Knowing the encoding methodology it was trivial to manually translate the bits for later use in an Arduino transmitter sketch. We find it amazing how simple [Dave] makes the process seem, even choosing to write his own sketch to reproduce and transmit the IR codes and carrier instead of taking the easy road looking for existing libraries.
A real gem of knowledge in the video was when it didn’t work! We get to follow along as [Dave] stumbles before using a Saleae Logic analyzer to see that his transmitter was off frequency even though the math in his sketch seemed correct. Realizing the digital write routine was causing a slowdown he fudged his math to make the needed frequency correction. Sure, he could have removed the performance glitch by writing some custom port control but logic dictates using the fastest and simplest solution when hacking a one-off solution.
[Dave’s] video and links to source code after the break.
Continue reading “Learn to Translate IR Codes and Retransmit Using Arduino”
This is an overview of a 500,000 Watt radio transmitter site. It’s one of the slides shared in a guided video tour of the transmitter’s hardware. The radio station — whose call sign was WLW — called itself the Nation’s Station because of its ability to reach so much of the country.
It operated at the 500 kW level starting back in the 1930’s. The technology at the time meant that there were a lot of challenges involved with transmitting at this level of power. It took 750 kW input to achieve the 500 kW output. To reach that the station had a set of AC motors in the basement generating the 4500 Amps at 33 Volts DC
needed to power the transmitter to heat each filament. Obviously there was a lot of heat generated at the same time. The system was water-cooled. An elaborate network of Pyrex pipes carried distilled water to and from the tubes to handle the heat dissipation.
The video tour lasts about thirty minutes. It’s just packed with interesting tidbits from the experts leading the tour so add it to your watch list for some geeky entertainment over the weekend.
Continue reading “Retrotechtacular: A tour of WLW, a 500,000 Watt radio transmitter”
The GoPro line of HD cameras seem like they were specifically designed for use with quadcopters. We say that because the small, light-weight video devices present a payload which can be lifted without too much strain, but still have enough horse power to capture video of superb quality. Here’s a hack that uses the camera to provide a remote First Person View so that you may pilot the aircraft when it is out of your line of sight.
The camera in question is a GoPro Hero 3. It differs from its predecessors in that the composite video out port has been moved to a mini USB connector. But it’s still there and just a bit of cable splicing will yield a very clear signal. The image above shows the camera in the middle, connecting via the spliced cable to an FPV transmitter on the right. This will all be strapped to the quadcopter, with the signal picked up by the receiver on the left and piped to a goggle display worn by the pilot. You can see the cable being construction process in the clip after the break.
If you’re looking for other cool stuff to do with your GoPro camera check out the bullet-time work [Caleb] did with ours.
Continue reading “GoPro hack delivers live video feed for piloting your Quadcopter”
Get your feet wet with radio frequency transmitters and receivers by working your way through this pair of tutorials. [Chris] built the hardware around a couple of 555 timers so you don’t need to worry about any microcontroller programming. He started by building the transmitter and finished by constructing a receiver.
Apparently the 27 MHz band is okay to work with in most countries as long as your hardware stays below a certain power threshold. The carrier frequency is generated by the transmitter with the help of a 27.145 MHz crystal. The signal is picked up by the receiver which uses a hand-wrapped inductor made using an AL=25 Toroid Core. We’d say these are the parts that will be the hardest to find without putting in an order from a distributor. But the rest of the build just uses a couple 555 timer chips and passive components, all of which will be easy to find. The video after the break shows the project used to receive a Morse-code-style message entered with a push button. It would be fun to interface this with your microcontroller of choice and implement your own one-way error correction scheme.
About thirty cents and some wire are all it takes to start hacking extra features into this DX6i transmitter. The DX6i is a six-channel, two-mode transmitter used to control hobby airplanes and helicopters. There are several built-in features but [Ligius] found an easy way to add a few more. In the upper left portion of the case you can see the eight-pin microcontroller he brought to the project.
It’s a PIC 10F222 mounted in a DIP socket so that it may be removed for reprogramming. The hardware page of the wiki shows the connections he made. By reading from the throttle, and tapping into the trainer wire, he is able to add features without any apparent alterations to the controller (no extra buttons, etc). You can see in the clip after the break that the throttle position when power is switched on selects between different modes. This can be the delay for turning off the LCD backlight, or presets for helicopter or airplane modes. [Ligius] thinks there’s a lot more potential here, even the possibility of fixing a bug in this particular model of transmitter.
Continue reading “Adding features to a DX6i transmitter”
[Angus McInnes] has been working on AM radio transmission techniques. He tried out a method of using a VGA port for the task but found the vertical blanking was audible. His latest experiments use a Teensy microcontroller board as an AM transmitter.
This is not a standalone solution, but rather a hardware extension for his laptop. This is because the microprocessor doesn’t have enough cycles to do much more than read bytes over USB and push their bits out one of the I/O pins.
To get a steady stream of data he’s using isochronous mode to push a steady data stream via the USB connection. Bulk transfer is another option but [Angus] found that it caused some jitter in the audio. Each byte is fed to the AVR SPI hardware once every eight clock cycles. His transmission can be picked up from across the room, but that’s the limit since the AVR doesn’t put out that strong of a signal. But it should be a rather trivial exercise to build a simple amplifier.
Here’s a way of transmitting audio that makes it virtually impossible for someone else to listen in. Instead of sending radio waves bouncing all over creation, this uses the focused light of a laser to transmit audio. In the image above you can see the silver cylinder which houses the laser diode. It is focusing the beam on a light dependent resistor to the right which looks almost like a red LED due to the intensity of the light.
The simplicity of this circuit is fascinating. On the receiving end there is no more than the LDR, a 1.5V power source, and a headphone jack. The transmitter is not much more complicated than that. It includes an audio output transformer which boosts the resistance of the audio signal. This increase in resistance ensures that the laser diode modulates enough to affect the LDR on the receiving end. The transmitter uses a 3.3V supply. Check out the video after the break to hear the high quality of audio coming through the setup.
Once you’re done playing around with the transmitter you might try turning the laser into a remote control for your stereo.
Continue reading “A laser audio transmitter”