The crystal radio is a timeless learning experience, often our first insight into how a radio works. For some of us that childhood fascination never dies. Take for example Jim Cushman, this guy loves to work on vintage scooters, motorcycles, and especially crystal radios (special thanks to fellow coil-winding enthusiast M. Rosen for providing the link). Digging more deeply we find an entire community devoted to crystal radio design. In this article we will get back to basics and study the fundamentals of radio receiver design.
How it works:
A crystal radio is basically a high Q resonator tied to an antenna and an envelope detector. These days the envelope detector is a point contact diode such as a 1N34 Germanium diode.
The resonant circuit passes a specific wavelength (or more specifically range of wavelengths depending on its Q). The diode detector provides the amplitude or envelope of the signal(s) within that wavelength. A high impedance or highly sensitive ear piece converts this envelope to an audible signal that you can listen to.
The neat thing about crystal radios is that no active RF amplification is used. The radio is powered by the incoming radio signal that it is tuned to. More sophisticated crystal sets might have more than one tuned stage, perhaps 3 or 4 to minimize receiver bandwidth for maximum sensitivity and selectivity.
Continue reading “Getting Serious about Crystal Radios”
1977 was a special year for computing history; this year saw the release of the 8085 following the release of the Z80 a year before. Three companies would launch their first true production computers in 1977: Apple released the Apple II, Commodore the PET 2001, and Tandy / Radio Shack the TRS-80 Model I. These were all incredibly limited machines, but at least one of them can still be used to browse Wikipedia.
[Pete]’s TRSWiki is a Wikipedia client for the TRS-80 Model I that is able to look up millions of articles in only uppercase characters, and low resolution (128×48) graphics. It’s doing this over Ethernet with a very cool Model I System Expander (MISE) that brings the lowly Trash-80 into the modern era.
The MISE is capable of booting from CF cards, driving an SVGA display and connecting to 10/100 Ethernet. Connecting to the Internet over Ethernet is one thing, but requesting and loading a web page is another thing entirely. There’s not much chance of large images or gigantic walls of text fitting in the TRS-80’s RAM, so [Pete] is using a proxy server on an Amazon Web Services box. This proxy is written in Java, but the code running on the TRS-80 is written entirely in Z80 assembly; not bad for [Pete]’s first project in Z80 assembly.
If you have an old computer you’d like featured, just load up the retro site, snap some pictures, have them developed, and send them in.
Some projects that we build fulfill a genuine need for a new piece of hardware or software that will make life easier or fix a common problem. Other projects, on the other hand, we do just because it’s possible to do. [Gilchrist] has finished work on a project that fits squarely in the second category: a web browser that runs exclusively on an Arduino Uno with an ethernet shield.
The Arduino can serve plain-text web pages to an attached LCD and can follow hyperlinks. User input is handled by a small joystick, but the impressive part of the build is on the software side. The Arduino only has 2KB of RAM to handle web pages, and the required libraries take up 20KB of memory, leaving only about 12 KB for the HTML parser/renderer and the LCD renderer.
The Arduino browser is a work in progress, and [Gilchrist] mentions that goals for the project include more robustness to handle poor HTML (the Hackaday retro edition loads flawlessly though), a terminal, and WiFi capabilities. To that end, maybe a good solution would be using the new ESP8266 chip to keep things small and inexpensive?
Our friends over at Hack42 in the Netherlands decided to have some fun with their computer museum. So far, they’ve been able to display the Hack a Day retro site on three classic computers — including an Apple Lisa, a DEC GIGI, and a run of the mill DEC VT100. We had the opportunity to visit Hack42 last October during our Hackerspacing in Europe trip — but just as a refresher if you don’t remember, Hack42 is in Arnhem, in the Netherlands — just outside of Germany. The compound was built in 1942 as a German military base, disguised as a bunch of farmhouses. It is now home to Hack42, artist studios, and other random businesses. The neat thing is, its location is still blurred out on Google Maps! Needless to say, their hackerspace has lots of space. Seriously. So much so they have their own computer museum! Which is why they’ve decided to have some fun with them… Continue reading “Hack A Day Goes Retro in a Computer Museum”