27 MHz transmitter/receiver pair made with 555 timers

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.

Adding features to a DX6i transmitter

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.

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Teensy board used as an AM radio 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.

A laser audio transmitter

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.

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Need a quadcopter transmitter? Use a PS2 controller!

After [Pyrofer] built a quadcopter, he purchased a cheap 6-channel transmitter made in China. Unfortunately, that transmitter was terrible so he took an old PS2 controller and built his own.

For his build, [Pyrofer] broke out the analog sticks and wired them to an AVR housed in the handle of the controller. The AVR sent commands to a 2.4 GHz radio transmitter powered by a small LiPo battery. With the addition of a few tact switches behind the shoulder buttons of the controller, [Pyrofer] has four axes of control with a few buttons for changing modes on his quadcopter.

This build really doesn’t hold a candle to some of the awesome DIY RC transmitters we’ve seen, but we’ve got to give [Pyrofer] credit for coming up with a very simple and easy build. Just about everyone has a PS2 or XBox controller lying around, and with a few extra hardware bits it’s easy to bodge up a decent remote control.

[Pyrofer] used a project called Funkenschlag to generate PPM signals, so if you feel the need to replicate this project send it in when you’re done.

The RC transmitter that does everything

[Demetris] sent in a project he’s been working on over the last year. It’s called the Open Source Radio Control, and promises to be a modular platform for every imaginable remote control transmitter need. If you’d like to control a bipedal android or a 3D aerobatic model plane, the OSRC can do it while transmitting video from the cockpit down to your hands.

Last summer, we caught wind of the OSRC project to build an extensible and open source remote control radio that would do anything; from displaying video from the cockpit to serving as the brain of a UAV rig, the OSRC promised to do everything.

A fully decked out OSRC can be had for about $1400, putting it in the upper echelon of remote control radios. For that price, though, you get a fully customizable radio with your choice of shoulder buttons and a 4.8 inch LCD that receives a video feed from the cockpit of your favorite model. The base unit starts out around $700; still very expensive for a remote control radio, but reasonable when you consider all the possible upgrades.

[Demetris] and the rest of the team put together an outrageously long yet surprisingly beautiful video showing off a few features of the OSRC. You can check that out after the break.

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The folly of adding an auxiliary audio input to a Hyundai Sonata

Why auxiliary audio inputs haven’t been standard on automotive head units for decades is beyond us. But you can bet that if you’re looking at a low-priced sedan you’ll need to buy an entire upgrade package just to get an audio jack on the dash. [Jon W’s] Hyundai Sonata didn’t have that bells-and-whistles upgrade so he decided to pop his stereo out and add his own aux port.

A big portion of this hack is just getting the head unit out of the dash. This is made difficult on purpose as an anti-theft feature, but [Jon’s] judicious use of a butter knife seemed to do the trick. He lost some small bits along the way which were recovered with a Shish Kebab skewer with double-stick tape on the end.

With the head unit out, he opened the case and plied his professional Electrical Engineering skills to adding the input. Well, he meant to, but it turns out there’s no magic bullet here. The setup inside the unit offered no easy way to solder up an input that would work. Having done all of the disassembly he wasn’t going to let it go to waste. [Jon] grabbed a nice FM transmitter setup. He wired it up inside the dash and mounted the interface parts in the glove box as seen here.

It’s nice to know we’re not the only ones who sometimes fail at achieving our seemingly simple hacking goals. At least [Jon] was able to rally and end up with the functionality he was looking for.