Crystal Oven Temperature Sensor Reads 0.01F Resolution

June 19, 2013 by Mike Szczys 17 Comments

crystal-oven-temperature-sensor

[Scott Harden] continues his work on a high precision crystal oven. Being able to set a precise temperature depends on the ability to measure temperature with precision as well. That’s where this circuit comes in. It’s based around an LM335 linear temperature sensor. He’s designed support circuitry that can read temperature with hundredth-of-a-degree resolution.

Reading the sensor directly with an AVR microcontroller’s Analog-to-Digital Converter (ADC) will only yield about 1-2 degrees of range. He approached the problem by amplifying the output of the sensor to target a specific range. For the demonstration he adjusts the swing from 0-5V to correspond to a room temperature to body temperature range.

Of course he’s using analog circuitry to make this happen. But before our digital-only readers click away you should view his video explanation. This exhibits the base functionality of OpAmps. And we think [Scott] did a great job of presenting the concepts by providing a clear and readable schematic and explaining each part slowly and completely.

So what’s this crystal oven we mentioned? It’s a radio project that goes back several years.

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Telegraph Sounder Clicks Out Email Messages

June 12, 2013 by Mike Szczys 7 Comments

telegraph-box-together

[Patrick Schless] is excited to show off the project he took on about nine months ago. After finding an antique telegraph sounder he wired it up to an Arduino to see if he could make it tick. The successful experiment laid the ground work for different hardware that would make it into a morse code email reader.

He doesn’t know much about the background of the old hardware, but driving it is relatively simple. It’s basically a magnetic relay so you need to have a transistor for switching and a flyback diode for protection. Once those components are in place it’s just a matter of toggling a bit. [Patrick] knew he wanted to pull messages from an online source, so he set his Arduino aside and grabbed a Raspberry Pi. It worked like a charm. His plan was to put this on a bookshelf in perpetuity so he went the extra mile, designing his own PCB and having it spun using the OSH Park service. The project is finished with this low-profile laser-cut base which houses all of the electronics.

Now if he wants to respond to his emails in Morse code he needs to build this keyboard.

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Hacking The R-390A Military Shortwave Radio Receiver To Transmit As Well

June 6, 2013 by Mike Szczys 12 Comments

hacking-r390a-radio

After getting his hands on this relic [Gregory Charvat] manage to hack it, converting the receiver into a transceiver.

It may be old, but the R-390A is nothing to scoff at. It’s abilities include AM, code, and FSK operation from 500 kHz to 32 MHz. But it is a receiver with no way of transmitting on the same bands. This is where [Gregory’s] hack comes into play. He rerouted the variable-frequency oscillator feed inside of the R-390A in order to use his 20M single-sideband unit. Basically what this does is allow him to control everything from the 390, using the microphone from the SSB — along with some switching hardware — to transmit his own messages.

His demo video starts with him making a few contacts using the hacked equipment. He then spends some time at the whiteboard explaning the changes. This portion went over our heads, but it becomes more clear when he cracks open the case and shows the actual modifications.

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2013 LayerOne Badge Hacking Contest Winner

June 1, 2013 by Mike Szczys 20 Comments

[Dynotronix] wrote in to share the news that he won the 2013 LayerOne badge hacking contest. In addition to the good news he included a description of his badge hack.

We got a good look at the hardware included on the badge several days ago. You may remember that it’s outfitted with footprints for 48 LEDs around the perimeter which are driven by two ICs. Looking at the image above it’s hard to miss the fact that [Dyno] didn’t populate any of that. He went right for the power of the XMEGA processor to analyze and generate signals.

But what specifically can you do with the signal this thing generates? Turns out a rather simple circuit can make it into a transmitter. [Dyno] concedes that it’s a remarkably finicky setup, but just a few components on a scrap of copper clad turned this into an FM transmitter. Check out the video where you can hear the sweeping alarm-type sounds pushed to an FM radio via his voltage controlled oscillator circuit which has a range of about fifteen feet.

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Raspberry Pi Helps With 2.4GHz Home Automation

May 30, 2013 by Mike Szczys 15 Comments

Wanting to extend the capabilities of the radio frequency devices in his home [Kalle Löfgren] turned a Raspberry Pi into an RF control hub. We’ve seen some of his home automation work in the past. In his media room he built a universal remote base station which used the same RF board as in this project. The main difference is that before he went with an AVR microcontroller and this time he’s upgrade to a Raspberry Pi board.

The RPi brings a lot more to the table. Notably, the scripting (whose output is shown above) and networking features. His radio board is an nRF24L01 which he talks to via the SPI protocol. The Raspberry Pi has no problem talking to SPI devices through its GPIO header. [Kalle] just needed to do a bit of setup to configure the pin modes.

A Python script lets him sent commands using his keyboard, but this can also be automated. Combine that with the TCP server script he wrote and it opens up the a wide range of configurations to switch or talk to any device operating on the 2.4 GHz band.

Detecting Galactic Rotation With Software Defined Radio

May 26, 2013 by Brian Benchoff 27 Comments

Last summer in the heyday of software defined radio via USB TV tuners we asked hackaday readers a question: Is anyone using everyone’s favorite method of SDR for radio astronomy? It took nearly a year, but finally there’s an awesome project to turn a USB TV tuner into a radio telescope. It’s from the fruitful mind of [Marcus Leech] (PDF warning), and is good enough to detect the rotation of the galaxy with a three-foot satellite dish.

News of [Marcus]’ work comes to us from [Carl] over at RTL-SDR.com who has been keeping tabs on the advances of building a radio telescope in a backyard. He’s been collecting a lot of interesting tidbits including this gif showing an arm of the galaxy entering and leaving [Marcus]’ telescope’s field of view over the course of a few hours.

Not only can [Marcus]’ telescope record continium measurements – basically, a single-pixel camera sensitive to only one frequency – it can also produce spectral plots of the sky. Combine the ability to measure multiple frequencies at the same time with the Doppler effect, and [Marcus] can measure the rotation of the galaxy with a USB TV tuner. That’s just awesome in our humble opinion.

If you already have an RTL-SDR TV tuner and a largish satellite dish, [Marcus]’ project should be fairly inexpensive to replicate; the feed assembly is made out of a coffee can, the amplifiers are repurposed satellite television equipment, and all the software – [Marcus]’ own simple_ra tool for GNU Radio – is open source. Of course with a 3 foot diameter dish, it will be impossible to replicate the data from huge radio telescopes. Still, it’s an impressive piece of work that leaves us searching craigslist for an old C-band dish.