A Vintage Single Transistor LED Blinker

October 17, 2016 by 19 Comments

[Eric Wasatonic] had a box of SWB2433 transistors that he had very little information about. In order to discover their properties, he fired up his curve tracer to compare these transistors with more common ones. He noticed the SWB2433 exhibited negative resistance while the similar curves of a 2n3904 didn’t. Then he reverse-biased the two transistors: the negative resistance region on the 2n3904 was less than that of the SWB2433, but it was there, and a 2n2222 had a bigger region. Using this knowledge, he developed a relaxation oscillator circuit which uses a negatively biased transistor.

Using one transistor, one resistor and one capacitor, he describes the circuit and how the components affect the frequency of the sawtooth wave the oscillator creates. [Eric] uses the oscillator to build a simple LED blinker and shows what happens when he changes the transistor and adjusts the voltage or resistance. He also shows the circuit as a tone generator and adjusts the tone by replacing the resistor with a potentiometer. And then, for fun, he modifies the circuit to show the oscillator as an AM transmitter. Check out his video after the break.

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Hackaday Prize Entry: The Internet Of Casts

October 16, 2016 by 5 Comments

[Alex]’s entry for the Hackaday Prize is extremely simple: it’s a device to monitor the inside of casts. For every itch, for every broken bone, for every skin irritation, and for every episode of House that featured compartment syndrome, the CastMinder has an answer.

The CastMinder is a simple electronic device embedded inside an orthopedic cast. Attached to this tiny bit of electronics are a few sensors, relaying pressure, moisture, temperature, and of course the battery level to an iOS app. The use case for this device is actually very simple; the pressure sensor is a great idea if you have a cast and you’re unconscious in a hospital. A moisture sensor will at least tell you how many trash bags wrapped around your broken arm are necessary to take a shower.

The entire device is based on the LightBlue Bean, a tiny Bluetooth-enabled device that can be powered by a CR2032 battery. The enclosure is 3D printed, and the entire device is small enough to be embedded in a cast without the wearer noticing much. It’s a great idea, and a great project to make it to the semifinals of the Hackaday Prize.

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A Robot Arm From The Cupboard

October 16, 2016 by 4 Comments

Building a simple robot arm is a lot more straightforward than it used to be.  If you have a laser cutter, or a bit of cash and don’t mind waiting for postage, there are inexpensive kits like the MeArm. If you have a 3D printer, there are any number of 3D-printed designs for you to tackle. What if you need to satisfy your urge to build a robot arm really quickly, and you don’t have a laser cutter or 3D printer? You’ve got a pile of servos from that remote-control project, how can you make the rest?

If you are [roboteurs], you raid the stationery cupboard, and create an arm using rubber bands, paper clips, and binder clips. The binder clips grip the servo arms and hold the whole thing together, the rubber bands provide extra attachment , and the paper clips are bent to form the jaws. It’s not the prettiest or perhaps the most capable of arms, but it undeniably is an arm, and we’d doubt it could be done any more cheaply.

In this particular case, the arm serves as a demonstration piece for [roboteurs]’ Printabots Maker Kit for people without a 3D printer. It uses their controller board, but there is no reason why it could not be used with any other board capable of driving servos.

We’ve covered innumerable robot arms over the years, This one may be the cheapest, but another contender might be this cardboard arm. None of them, however, are as cool as this steam-powered Armatron toy.

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Hackaday Links: October 16, 2016

October 16, 2016 by 35 Comments

You need only look at the weekly user account leak from a popular web service or platform to know there’s a problem with security. Reusing passwords is the dumbest thing you can do right now, and the Mooltipass Mini is the answer to that problem. The Mooltipass originally began as a Developed on Hackaday series, and we log frequent sightings of the Multipass (maxi?) at security cons. The Mini is smaller, has exactly the same capability, and is completely unrepairable. It’s very cool, and if your email password is the same as your banking account passwords, you kind of need this yesterday.

Last weekend was the Open Hardware Summit in Portland. All the talks were worth watching, but editing the talks down into something sensible takes time. In lieu of this, OSHPark has gone through the livestream and timestamped everything

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A Cheap, 555-Based Geiger Counter

October 16, 2016 by 37 Comments

Every mad scientist’s lair needs a Geiger counter. After all, if that UFO crashes on the back patio, you might need to know if it is hot. [Tanner_Tech] shows you how to build a cheap one that will get the job done.

You do need a Geiger tube, but a quick search of a popular auction site shows plenty of Russian surplus for a few bucks. The other thing you need is a source of high voltage (about 400V), which is the heart of the circuit using a 555-based DC to DC converter. You can see a video of the device working, below.

The DC to DC converter needs a transformer that [Tanner] swiped out of an alarm clock. A piezo transducer (stolen from a junk microwave) gives you the characteristic click. If you prefer solid state over hollow state, there’s an open source project that uses a PIN diode as a sensor. Or you could add an Arduino and some LEDs.

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Upcycle An Isolation Transformer

October 16, 2016 by 40 Comments

There are several reasons you should have an isolation transformer. They can prevent ground loops and also prevent a device under test from having a DC path to ground (or isolate an oscilloscope from DC ground, which can be dangerous in its own right, but that’s another discussion). [Tanner_tech] noticed that finding ballast transformers for sodium vapor street lights is getting easier as more street lights move to LED technology. What to do with these transformers? Build an isolation transformer, of course.

Of course, your dumpster transformer might be a little different than the one shown in the post (and the video, below). [Tanner] shows how to work out the leads you need. A little wood work and a PC power supply case finished the project.

Judging from the comments, some people take [Tanner’s] talk about safety as an implication that a transformer makes working on mains safe. It doesn’t. It makes it safer if you know what you are doing. Working with high voltage isn’t a place to learn by doing.

If you want some practical advice, [Jenny List] has a good read for you. You probably also ought to invest an hour in watching this video that has a lot of practical advice.

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Teardown A Classic : Tektronix P6042 Current Probe

October 16, 2016 by 6 Comments

[Paul Rako]’s teardown of his treasured P6042 current probe shows why Tektronix commands so much respect among the old hats of the electronics world.

Built in 1969, the P6042 is pretty sparse transistor-wise when compared a modern sensor. The user would clip the current probe, permanently attached to the case since the circuit was tuned for each one, over a wire and view the change in volts on an oscilloscope. When the voltage division on the oscilloscope was set properly the current in a circuit could be easily seen.

The teardown is of a working unit so it’s not completely disassembled, but it also sits as a nice guide on refurbishing your own P6043, if you manage to snag one from somewhere. Aside from capacitors and oxidized switch contacts there’s not much that can go wrong with this one.

As for how it compares, the linear power supply, analog circuit design, and general excellent engineering has the P6042 coming in with a cleaner signal than some newer models. Not bad for a relic! Do any of you have a favorite old bit of measurement kit?