A SI5351 clock generator chip and an Arduino

Generate Clocks With The SI5351 And An Arduino

June 27, 2014 by Eric Evenchick 10 Comments

If you’re dealing with RF, you’ll probably have the need to generate a variety of clock signals. Fortunately, [Jason] has applied his knowledge to build a SI5351 library for the Arduino and a breakout board for the chip.

The SI5351 is a programmable clock generator. It can output up to eight unique frequencies at 8 kHz to 133 MHz. This makes it a handy tool for building up RF projects. [Jason]’s breakout board provides 3 isolated clock outputs on SMA connectors. A header connects to an Arduino, which provides power and control over I2C.

If you’re looking for an application, [Jason]’s prototype single-sideband radio shows the chip in action. This radio uses two of the SI5351 clocks: one for the VFO and one for the BFO. This reduces the part count, and could make this design quite cheap.

The Arduino library is available on Github, and you can order a SI5351 breakout board from OSHPark.

Controlling RC Toys With The Raspi

June 3, 2014 by Brian Benchoff 18 Comments

signal

An interesting trick you can do with a a fast CPU and a GPIO pin mapped directly to memory is an FM transmitter. Just toggle a pin on and off fast enough, and you have a crude and kludgy transmitter. [Brandon] saw a few builds that turned a Raspberry Pi into an FM radio transmitter and realized a lot of toy remote control cars use a frequency in the same range a Pi can transmit at. It’s not much of a leap to realize the Pi can control these remote control cars using only a length of wire attached to a GPIO pin.

The original hack that turned a Pi GPIO pin into an FM transmitter mapped a GPIO pin to memory, cycled through that memory at about 100 MHz, and added a fractional divider to slightly adjust the frequency, turning it into an FM transmitter. Cheap RC cars usually listen for radio signals at 27 and 49 MHz. It doesn’t take much to realize commanding RC cars with a Pi is possible.

The only problem with this idea is that most RC cars use pulse modulation. For an RC transmitter to send the command for ‘forward’, a synchronization pulse is sent, then a series of pulses and pauses. The frequency doesn’t change at all, something the originally FM code doesn’t do. [Brandon] realized that if he just moved the frequency up to something the RC car wasn’t listening to, that would register as a zero.

All that was left was to figure out the command codes for his RC truck. For this, [Brandon] decided brute force would be the best option. Armed with a script and a webcam, he cycled through all possible combinations until the webcam detected a moving truck. Subtlety brilliant, if you ask us. Of course more complex commands required an oscilloscope, but now [Brandon] has a git full of all the code to control a cheap RC car with a Pi.

Talking To ISEE-3

May 29, 2014 by Brian Benchoff 18 Comments

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ISEE-3, the plucky interplanetary spacecraft fueled by the dreams of thousands of crowdfunding backers and hydrazine is now transmitting data to Earth.

Where all radio contact with ISEE-3 this year has only been a carrier frequency, the folks at the reboot project have successfully commanded ISSE via the huge Arecibo telescope to transmit data back to Earth. Usable data are now being received at 512 bits/second at ground stations in Germany, Kentucky, and California, surely being looked over by the ISEE reboot project engineers.

Simply transmitting the commands to put the data multiplexers into their engineering telemetry mode was no small task; a power amplifier needed to be built, shipped to Arecibo, and installed in the giant dome hanging over the Arecibo dish. The amplifier was only installed in the last day, during an earthquake, no less.

There’s still a lot of work to be done before the project can go any further; the team will need to check the status of the spacecraft from the data received, more systems will be checked out, and eventually the spacecraft will be commanded to perform a 17-hour long burn with its small thrusters, putting it on course to be captured by Earth some time in August.

It’s an amazing achievement to do any sort of communication on this scale, and now events in the ISEE-3 mission timeline will be coming rather quickly. We’re trying to organize a video/blog/cast thing with the team from NASA Ames or Morehead State, but the team is, understandably, a little busy right now.

Oinker Is Twitter For HAMs

May 12, 2014 by Rick Osgood 57 Comments

Have you ever wanted to send a quick message to your HAM radio buddies over the air but then realized you forgot your radio at home? [Troy] created Oinker to remedy this problem. Oinker is a Perl script that turns emails into audio.

The script monitors an email account for new messages and then uses the Festival text-to-speech engine to transform the text into audio. [Troy] runs Oinker on a Raspberry Pi, with the Pi’s audio output plugged directly into an inexpensive ham radio. The radio is then manually tuned to the desired transmit frequency. Whenever Oinker see’s a new email, that message is converted into speech and then output to the transmitter.

The script automatically appends your HAM radio call sign to the end of every message to ensure you stay within FCC regulations. Now whenever [Troy] runs into some bad traffic on the road, he can send a quick SMS to his email address and warn his HAM radio buddies to stay clear of the area.

Repairing A Damaged RC Rx Due To Reverse Polarity Power Input

May 12, 2014 by Rich Bremer 21 Comments

Rx Receiver Repair

Once in a while all of us technocenti get a little complacent and do something that may be considered ‘dumb’ while working on a project…. like cutting the wrong side of a piece of wood or welding a bracket on in the wrong direction. [Santhosh] is human like everyone else and plugged in the power connector to his RC Receiver incorrectly, rendering the receiver useless. How will his Arduino-controlled Robot work without a functioning receiver?

[Santhosh] started by opening up the case to expose the circuit board and checking out the components inside. The first component in the power input path was a voltage regulator. Five volts DC was applied to the input side of the 3.3-volt regulator but only 1.21 came out the other end. Now that the problem was quickly identified the next step was to replace the faulty regulator. Purchasing an exact replacement would have been easy but cost both time and money. [Santhosh]’s parts bin contained a similar regulator, a little larger than the original but the pinout was the same.

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Reading 2.4GHz Transmitters With An Arduino

May 10, 2014 by Brian Benchoff 11 Comments

Quad There are a lot of cheap quadcopter kits out there, sold ready to fly with a transmitter and battery for right around $50 USD. One of the more popular of these micro quads is the V2X2 series. They are, unfortunately not compatible with any other radio protocol out there, but [Alexandre] has managed to use the transmitter included with his V202 quad to send data to an Arduino.

Like most quads, the transmitter that came with [Alexandre]’s V202 operates on 2.4GHz. Listening in on that band required a little bit of hardware, in this case a nordic Semiconductors nRF24L01p. Attached to this chip is a regular ‘ol Arduino running a bit of code that includes [Alexandre]’s V202 library.

Right now, the build can detect if the quad is bound or not, and read the current position of the throttle, yaw, pitch, and roll, as well as all the associated trims. It’s just the beginnings of [Alexandre]’s project, but his eventual goal is to build an Arduino bot based on the code, complete with RC servos. Not bad for a transmitter that will be utterly useless when the microquad eventually breaks.

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DIY Ultra Wideband Impulse Synthetic Aperture Radar And A MakerBot

May 7, 2014 by Brian Benchoff 7 Comments

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What could possibly be better than printing out a few low-resolution voxels on a MakerBot? A whole lot of things, but how about getting those voxels with your own synthetic aperture radar? That’s what [Gregory Charvat] has been up to, and he’s documented the entire process for us.

The build began with an ultra wideband impulse radar we saw a while ago. The radar is built from scraps [Greg] picked up on eBay, and is able to image a scene in the time domain, creating nice linear sweeps on a MATLAB plot when [Greg] runs in front of the horns.

With an impulse radar under his belt, [Greg] moved up the technological ladder to something that can produce vaguely intelligible images with his setup. The synthetic aperture radar made from putting his radar horns on the carriage of a garage door opener. The horns slowly scan back and forth along the linear rail, taking single impulse readings and adding them together in an image. In the video below, [Greg] is able to image a few pieces of copper pipe only a few inches in diameter. The necessary equipment for this build only cost [Greg] a few hundred bucks at the Dayton Hamvention, and a similar setup could be put together for even less.

If building an X band impulse synthetic aperture radar isn’t impressive enough. [Greg] also 3D printed one of his radar images on a MakerBot. That’s just applying stlwrite to the 2D radar image and feeding it into MakerWare. Gotta have that blog cred, doe. It also makes for the best headline I’ve ever written.

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