Getting Serious about Crystal Radios

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.

cs09-schematic

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.

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How to Be the Hardware Engineer at a Startup

For those who prefer the smell of solder smoke to lines of code then you may be a hardware engineer. What you should consider is how to land a job at a startup, how to work fast, be a team player, keep an open mind, and be organized. Joining a startup will be the greatest challenge of your career. You can do it! Be a hardware engineer at a startup and change the world.

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Shark vs. Robot

In laymen’s terms they built a shark-chasing robot. You can guess what happened next…

The back story is a little more reputable. I recently attended the Center for Marine Robotics meeting at the Woods Hole Oceanographic Institution (WHOI) and learned about a very interesting robot. For the Discovery Channel’s Shark Week the network partnered with [Amy Kukulya] at WHOI to develop an autonomous underwater vehicle (AUV) that locates, follows, and films sharks in their natural habitats, swimming, patrolling, doing their thing.

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See Actual Microwaves — No More Faking It

Last week we saw a lot of interest in faux visualization of wireless signals. It used a tablet as an interface device to show you what the wireless signals around you looked like and was kind of impressive if you squinted your eyes and didn’t think too much about it. But for me it was disappointing because I know it is actually possible to see what radio waves look like. In this post I will show you how to actually do it by modifying a coffee can radar which you can build at home.

The late great Prof. David Staelin from MIT once told me once that, ‘if you make a new instrument and point it at nature you will learn something new.’ Of all the things I’ve pointed Coffee Can Radars at, one of the most interesting thus far is the direct measurement and visualization of 2.4 GHz radiation which is in use in our WiFi, cordless phones (if you still have one) and many other consumer goods. There is no need to fool yourself with fake visualizations when you can do it for real.

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Mechanical Watch Hacker Gets an Apple Watch

Mechanical watch enthusiasts see the Apple watch as a threat to the traditional gear train. It does not tick, requires frequent re-charging, and it’s certainly not the most attractive of watches. But it can direct you to the local coffee shop, allow you to communicate with friends anywhere in the world, get you onto an airplane after the most awkward of arm gestures, and keep you apprised of the latest NCAA basketball scores. Is the advent of the smart watch the end to the mechanical watch?
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Become a Mad Scientist, Build A Power Distribution Panel

One practical use of large switches and indicator lamps is to make a power distribution panel which can be useful when you want to control and monitor the power consumption of numerous devices such as your electronics work bench or amateur radio station. Old-school in appearance and using military surplus electronics, this power distribution panel allows for control of outlet on back. Did I mention I built it when I was 16?

Building it was easy, 120 VAC line enters through a main breaker. It is fed through an AC amp meter (with built-in shunt) then to a line filter. From the line filter it goes to a line voltage meter and filament transformer to power the indicator lamps. This AC line is then bussed out to the circuit breakers. Each breaker controls one outlet on the rear panel. As devices are switched on or off the current draw can be measured. This is well demonstrated in the video overview found after the break.

Be creative. Use military surplus switches, indicators, and other unique looking hardware. Customize to give your preferred mad scientist look while also providing valuable functionality.

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Vintage Electronics Magazines Predicted Our Current Future

Do you remember the magazine Popular Electronics? What about Radio Electronics? These magazines were often the first exposure we had to the world of hacking. In December we learned that Americanradiohistory.com has gone to the trouble of scanning nearly every copy of both, and continues to add many many others — posting them online for us to enjoy once more. Since then we’ve been pouring through the archive pulling out some of the best in terms of nostalgia, entertainment, and fascinating engineering.

Yes much of this material is very dated; CB Radios, all-mighty computers, phasors, stun guns, levitating machines, overly complex circuits for simple tasks, and aviator eyeglasses. But found among all of this, many innovative mixed-signal circuits and other interesting ideas that have been developed into our tech-centric world. Many of those modern inventions you’ve welcomed into your life actually started long-long ago in the forward-thinking hacks shown off in these publications. The Google Glass precursor seen above is but one example. Keep reading to see the early roots of the tech we tend to think of as “new”.

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