Current Limiting Diode Use And Tutorial

January 6, 2014 by Todd Harrison 20 Comments

Not that this happens often, but what do you do when faced with a repair where you don’t know the power source but you do know you have to drive LED backlighting? When faced with this dilemma [Eric Wasatonic’s] solution was to design for ambiguity. In this interesting hack repair [Eric] needed to restore backlighting for an old car stereo LCD display. First he guaranteed he was working with a DC power source by inserting a small full-wave bridge rectifier. Then knowing he needed 4 mA to power each LED for backlighting he used some 1978 vintage current limiting diodes designed to pass 2mA each regardless of voltage source, within limits of course.

Sure this is a simple hack repair but worthy of being included in anyone’s bag of tricks. Like most hacks there is always knowledge to be gained. [Eric] shares a second video where he uses a curve tracer and some datasheets to understand how these old parts actually tick. These old 1N5305 current limiting diode regulators are simply constructed from a JFET with an internal feedback resistor to its gate which maintains a fixed current output. To demonstrate the simplicity of such a component, [Eric] constructs a current limiting circuit using a JFET and feedback potentiometer then confirms the functionality on a curve tracer. His fabricated simulation circuit worked perfectly.

There was a little money to be made with this repair which is always an added bonus, and the recipient never reported back with any problems so the fix is assumed successful. You can watch the two videos linked after the break, plus it would be interesting to hear your thoughts on what could have been done differently given the same circumstances.

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Hackaday: The Gathering

January 6, 2014 by Mike Szczys 83 Comments

1/21/14 – Downtown LA
Come one, come all to a party with [Brian], me, and the Hackaday readers who live in the Los Angeles area. Tickets are free, as is the beer, food, t-shirts, stickers, and other swag which you won’t find out about unless you show up in person.

This is the first official live Hackaday meetup and is open to all ages. During the summer we talked about making Hackaday a virtual hackerspace, and this event is one part of that initiative. We’ll let you in on some stuff we’ve been planning, but in return I expect you to tell us your thoughts on how the Hackaday community can get bigger and better. We’re also using the attendance at this event to judge if we should host more live events (possibly in other cities too). So if you’re in LA get your ticket now and make sure your friends do the same!

UPDATE 3: Get your name on the waiting list… Continue reading “Hackaday: The Gathering” →

Geek Group Fire Update

January 6, 2014 by Adam Fabio 167 Comments

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The Geek Group is in the process of cleaning up after their fire. Their small capacitor/spark gap room sustained the most damage, with the interior nearly completely incinerated, along with some structural damage to the walls and roof. The gap room was isolated from the much larger high voltage lab by red plastic welding curtain. The curtain was fire-retardant, but when it did finally burn, it was extremely sooty. With the curtain burning, soot covered the high voltage lab. The rest of the building escaped fire damage, but nearly all of it is covered in a fine layer of soot. The group has been and are attacking the soot problem head on, with shop-vacs, rags, and elbow grease. Several of their sponsors have also promised supplies to cover the remediation.

[Chris] and [Paul] have also been doing some sleuthing as to the root cause of the fire. While the cause will never be known beyond a shadow of a doubt, they have a pretty good idea of the chain of events. Gemini, the group’s 200 kVA Tesla coil had been run about 1/2 hour before smoke was detected. The fire was concentrated in Gemini’s spark gap room. Close inspection of the rotary spark gap showed that the stationary electrodes all seemed to have sustained a mechanical impact. It appears that either while the gap was running, or as it was spinning down, one of the flying electrodes moved enough to impact the stationary electrodes. These electrodes are 3/8″ and 1/2″ tungsten, and often glowed white-hot while the gap was in operation. One set screw held each electrode in to the 12″ rotor. The set screw of one flying electrode was found to be loose, and the electrode it retained probably impacted the stationary electrodes. It’s not a far leap to guess that hot metal from these impacts could have landed in the capacitor array, smoldered, and eventually caught aflame.

A single loose screw most likely caused the entire chain of events leading up to the fire. [Chris] and [Paul] had observed the spark gap throwing out hot bits of metal even during normal operation, and had planned an encapsulation box. However, disaster struck before it was built. This is not to say that The Geek Group operates an unsafe shop. The important thing here is that no one was hurt. Everyone in the building was evacuated quickly and safely.

A quick note about the comments – we know The Geek Group and [Chris] tend to be polarizing topics. However, we’d like to at try to keep the comments constructive.

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Doggy DVR Alarm Sensor

January 6, 2014 by James Hobson 10 Comments

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[Martin] lives in a small village about 25km from his job in a major city. Occasionally his home alarm system will trip and he will rush home to make sure everything is okay. So he decided to buy a DVR system instead… and he turned his dog’s collar into one of the main sensors.

As you may know, DVR’s also have sensor inputs in addition to loads of video cameras. These can be very handy to tell you other things that a small video clip will not, such as moisture, humidity, temperature etc. [Martin’s] DVR has 8 sensor inputs which he has configured to be the normally open type of sensors. By using a Sharp 817 optocoupler and a Funky v3 wireless module he made one of the sensor inputs wireless.

On the other end of the Funky wireless setup is a Kinder Surprise shell attached to his dog’s collar. In addition to the wireless module, it also contains a rudimentary 2-axis shock sensor consisting of a small spring that floats over a metal pin — when moved violently (when the dog is running about) it makes contact and [Martin’s] DVR alerts him by email and sends him pictures from the system.

He suspects he’ll be getting lots of pictures of the dog getting spooked by cats wandering by.

Automatic Antenna Tuner

January 6, 2014 by Eric Evenchick 48 Comments

To get the best power transfer into an antenna, tuning is required. This process uses a load to match the transmission line to the antenna, which controls the standing wave ratio (SWR).

[k3ng] built his own automatic antenna tuner. First, it measures the SWR of the line by using a tandem match coupler. This device allows the forward and reflected signals on the line to be extracted. They are buffered and fed into an Arduino for sampling. Using this data, the device can calculate the SWR. The RF signal is also divided and sampled to measure frequency.

To automate tuning, an Arduino switches a bank of capacitors and inductors in and out of the circuit. By varying the load, it can find the ideal matching for the given antenna and frequency. Once it does, the settings are stored in EEPROM so that they can be recalled later.

After the break, check out a video of the tuner clicking its relays and matching a load.

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The Most Beautiful Floppy Disk Jukebox Ever

January 5, 2014 by Brian Benchoff 22 Comments

Playing music on floppy drives is something that has been done to death. [kiu]’s RumbleRail is something else entirely. Yes, it’s still a collection of floppy drives playing MIDI files, but the engineering and build quality that went into this build puts it in a class by itself.

Instead of the usual assemblage of wires, power cords, and circuits that accompany most musical floppy drive builds, [kiu]’s is an exercise in precision and modularity. Each of the eight floppy drives are connected to its own driver with an ATMega16 microcontroller on board. The microcontrollers in these driver boards receive orders from the command board over an I2C bus. Since everything on the RumbleRail is modular, and the fact [kiu] is using DIP switches to set the I2C address of each board, this build could theoretically be expanded to 127 voices, or 127 individual floppy drives each playing their part of a MIDI file.

The RumbleRail can also operate in a standalone mode without the need for a separate computer feeding it data. MIDI files can be loaded off an SD card by the main controller board, and decode them for the floppy drivers.

If you’d like to build your own RumbleRail, all the board files, schematics, and firmware are up on [kiu]’s git. There are, of course, a few videos below of the floppy jukebox in action.

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Wireless Thermostat

January 5, 2014 by Kevin Darrah 15 Comments

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The thermostat in [Tom’s] 100-year-old house is two floors up from where the furnace is located, so a broken wire in the wall was just the catalyst needed to design a wireless thermostat.

The system is based on a customized PCB [Tom] designed called the Magic Mote. The board contains an MSP430 microcontroller, a low power NRF24l01+ wireless transceiver, and various sensor interfaces. The wireless thermostat project uses two of these boards; one monitors the temperature on the second floor and the other controls the furnace in the basement.

The temperature sensing is done using a DHT22/AM2303 temperature and humidity sensor, which is a convenient choice, since the part is calibrated and handles the analog digital conversion; you just need one digital pin to retrieve the temp/humidity data. To control the furnace, [Tom] used the local 24VAC and a latching relay to drive the heater signal. The 24VAC also powers the board, so a door-bell transformer steps the voltage down to something more usable; about 11VAC or so, which is then rectified, filtered, and regulated down to what the control electronics like to see (3.3V/5V).

This project is actually still in the early stages of what [Tom] has planned; a network of sensors and appliances with a beagle bone base station. We can’t wait to see what’s next for this project; maybe we’ll even see some voice control, like in this epic Siri controlled home automation project.

[via Dangerous Prototypes]