This toy intercom system is way better than a pair of tin cans and some string


On his blog, [Kenneth Finnegan] recently showed off a replica of a fun toy he used to play with as a kid, a telephone intercom system. The setup is pretty simple, requiring little more than a pair of analog phones, a battery, and a resistor.

The phones are connected to one another using a standard telephone cable, but [Kenneth] uses a 9v battery to introduce a small bias current into the loop, allowing the speakers at either end to hear one another. He also added a small LED into the circuit so that there is a visual indication as to when both handsets are off hook.

The setup is very simple at the moment, though [Kenneth] does have some ideas in mind to enhance his intercom system. He hopes to tweak the remote phone to ring when the local phone is picked up, among other things.

Telephone technology is nothing new, but for just a few dollars (or less) your kids can be entertained for hours as [Kenneth] was way back when.

Continue reading to see a short video overview of the phone system, and be sure to share your ideas for enhancing it in the comments section.

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ATtiny Hacks: SerialCouple – A standalone thermocouple ADC board with serial out

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Since we are in the midst of featuring a wide assortment of ATtiny hacks, [Kenneth] wrote in to share a project he has been developing over the last few months, the SerialCouple.

Most all development platforms have the ability to function as an analog to digital converter, but you don’t always need a full-featured board when all you require is serial output for your computer. With his SerialCouple board, [Kenneth] is trying to take some complexity out of the process by building a standalone thermocouple ADC board. The SerialCouple is designed to take analog readings from a thermocouple, converting them to digital values that can be sent to any device over a serial connection. The grunt work is done by a Maxim MAX31855 chip, which converts the thermocouple’s analog data to digital temperature readings. The digital representation of the temperature is then retrieved by the on-board ATtiny2313, which sends the data out the serial port.

If a standalone thermocouple ADC board is something you’ve been looking for, be sure to swing by his site to take a look at his code and schematics.

Continue reading to see a short video demo that explains how the SerialCouple works.

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Equipment Needed to Get “Started” in Electronics

[Kenneth] is a Mechanical Engineer who likes to dabble in electronics. Besides providing us with an excellent picture of his workbench, he has put together a list of things that you’ll need as you learn to work with electronics. A beginner electronics kit from one of a number of different sources may work for some, but others may not be interested in a kit.

[Kenneth] gives links and recommendations for categories of: books, electrical equipment, development tools, components, digital electronics, and analog chips. As he puts it, this post is a “gigantic list of everything I would buy right now to replace my entire workshop if mine were to disappear.”  This is a great list of things you may need if you’re starting out.  If you have some experience, this list may introduce you something new. Check out some of [Kenneth’s] other projects like his cloud chamber or the Chumby webserver that he made.

How Low Can You Go?

That’s exactly what [Kenneth Finnegan] figured out with his original investigation into low powered MSP430-based circuits. He was able to keep a count-up timer running off of 20F worth of capacitors for over 10 weeks. Although quite impressive by its own merit, many people left comments that questioned whether similar results would be seen in a circuit with functionality more advanced than simply incrementing a single digit on an LCD. Well folks, [Kenneth] has stepped it up again with this ultra low power LCD clock.

The biggest challenge in creating this clock was finding an efficient way to drive the 28 LCD segments off of the limited number of pins on his MSP430G2231 chip while still having open pins for button inputs as well. An ICM7211 LCD driver is definitely up for the task (with a few clever modifications to drive the auxiliary characters such as the center colon), but requires 8 pins to drive it. A standard 74HC595 latching shift register brings this number down to a more manageable number of 3 total pins.

Once completed the total current consumption was found to be around 12μA – low enough for a claimed run-time of approximately two and a half years from the 3V 200mAh CR2032 coin cell used. If true, a set of standard AA alkaline cells in series as found in many clocks would run this little circuit for decades.

Stick around for a short video after the break and make sure to check out the original blog entry for schematics and the complete source code!

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Your very own cloud chamber


[Kenneth] and [Jeff] spent a weekend building a cloud chamber. This is a detection device for radiation particles that are constantly bombarding the earth. It works by creating an environment of supersaturated alcohol vapor which condenses when struck by a particle travelling through the container, leaving a wispy trail behind. This was done on the cheap, using isopropyl alcohol and dry ice. They already had a beaker, and after a few tries figured out that the dry ice worked best when serving as a bed for the flask. A black piece of paper was added inside the base of the container to help raise the contrast when looking for condensate. They experimented with a couple of different methods for warming the alcohol, including an immersion heater built from power resistors.

There’s a video explaining the apparatus which we’ve embedded after the break. It’s a bit hard to see evidence of particle travel in the video but that’s all the more reason you should give this a try yourself.

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Chumby webserver using upgraded internal storage

The Chumby One has an internal SD card offering a fair amount of storage. [Kenneth Finnegan’s] came with a 1 GB card that had about 500 MB left over which he filled with a collection of MP3s. But he wanted to do more and so installed a pre-compiled version of lighttpd to act as a web server. The problem is that this binary requires a thumb drive to be plugged in because it maps the storage directory to the mounted USB folder. He wasn’t happy with that so he upgraded the internal SD card and rolled his own webserver to run from the internal SD card.

The upgrade involved going from a 1 GB to an 8 GB microSD card. In order to run the webserver internally he needed to recompile lighttpd to use a different root directory. This meant setting up an ARM cross-compiler and eventually finding a new place for the start up script. The location change for the ‘lighty’ directory leaves us wondering if a symlink couldn’t have solve the problem without recompilation. But we don’t have the hardware on hand to try this out ourselves.

But if you want to give it a shot, check out [Bunnie’s] post about Chumby-based hardware. Looks like you can head out to the big-box store and have one in hand without shelling out too many clams.

Launchpad takes ultra low power to the extreme

We’ve all known the MSP430s under the Launchpad are designed to be low power, but who wants to bet how long the chip can last on only 20F worth of capacitors? A couple of hours? A day at max? [Kenneth Finnegan] setup a MSP430 with supercaps to find out. To make sure the chip is actually running, [Kenneth] programmed it to count from 0 to 9 over a period of 10 seconds, and then reset. To get it ultra low power, the chip is in sleep mode most of the time, and a raw low current LCD is used to display the output. While [Kenneth] simply checks the chip every few hours to see if it’s still counting, a setup much like the Flash Destroyer, tracking a clock and then storing the current value would get a more exact time of death. Either way, it’s been over 3 weeks…and still counting. Video after the rift.

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