code, circuits, & construction

John Schimmel and I had a meeting with a friend the other day who has chronic condition, and is looking for tools to notify her family and friends of her activity at home, so she can live more independently. A lot of good ideas came up, making for a potentially exciting project that’d be useful someone we care about: a win-win situation.

One of the ideas she had was a bed sensor, which would let her family know whether she’s in bed or not, so they can call to either wake her up, or tell her to get some rest if she’s up too late. Inspired by Mustafa Bagdatli and Diego Rioja’s BedData project, and assisted by them, we thought we’d see if we could put something together quickly, connecting force sensing resistors to an Arduino and using an Ethernet shield to upload data to Pachube.  The project has not been tested in the field yet, but it’s working in the lab, and was simple to set up.  It may be a useful example for other sensor projects.

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Nicolas Villar sent me a sample of the PepperMill, a new sensor board he and Steve Hodges designed at Microsoft Research in Cambridge, UK.  It’s a nifty little board.  You attach a DC motor and the board can an output voltage when the motor is turned,  and analog signals telling you the direction and speed of the motor.  It turns a DC motor into a rotary encoder, of sorts.

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Coming late to the game, I’m trying out a Bluetooth Mate from SparkFun with an Arduino Lilypad.Overall, it’s a nice Bluetooth radio to use with microcontrollers.  A few thoughts on getting it working:

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Matt Mets has written a nice Nikon remote control library for Arduino. I used it to make a motion trigger and intervalometer. It looks like this:

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Here’s a Processing sketch that takes data from Sparkfun’s uLog datalogger via a serial port, and saves the results to a file. To use this, you’ll need:

• uLog datalogger with some data on it
• USB-to-serial adaptor; there are many types out there, but I used this one.

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Berkeley’s CNMAT (center for new music and audio technologies) has a nice resource archive, with pictures.  Useful if you’re looking for electronic parts, microphones, and other things audio-related.  Similar to RISDpedia and ITPedia, among others, very useful.  Thanks to Tom Gerhardt and Adrian Freed for the link.

Peter Knight works with Massimo and Alex and co. at Tinker.it. He’s written some great AVR code, which is useful in Arduino.  For example:

Secret Thermometer takes advantage of the ATMega’s internal thermometer. Turns your ‘328-based Arduino into a thermometer with no extra parts.

Secret Voltmeter same idea, but this reads the internal analog-to-digital converter to tell you the Arduino’s supply voltage. Also works on the ATMega168.

He’s also done Cantarino, a speech synthesis engine; Auduino, a granular sound synthesis engine; a DMX library; and more.  Check them all out at the tinker.it code repository.

Shigeru Kobayashi, who made Gainer and Funnel, has made yet another nifty tool for physical computing:  physical x wonderfl. It combines Gainer, Funnel, Firmata, Arduino, and Wonderfl.

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Making LED displays is fun. There are a a few tools that get used all the time, from row-column scanning to LED driver chips to multplexers and shift registers. This tutorial discusses some of the more popular methods for controlling large amounts of LEDs from a microcontroller, including their various strengths and weaknesses, and how they work. For more on this subject see chapter 14 of “Physical Computing“, where Dan O’Sullivan and I discussed it in more depth.  I’ll also include some notes on how to apply these ideas to controlling multiple motors or other high-current loads.

Most microcontroller modules have a limited number of outputs. Even if you use the analog inputs as digital I/O, there are only 19 pins on an Arduino, for example. That’s a fairly typical number for an 8-bit controller, and it seems not nearly enough if you want to control, say, 100 LEDs or more.  There are a couple ways around this problem.  Without adding any additional hardware, you can make a matrix of your LEDs and control them using row-column scanning.  If you want discrete analog control over one output at a time, you can use a multiplexer. For digital control over multiple pins, you could use an addressable latch or a shift register. If you need pseudo-analog control over multiple pins, you could use a PWM driver.  There are also several LED driver chips that are designed specifically to control groups of LEDS.

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This tutorial will show how to control multiple LED outputs from a microcontroller using a CD4099B  addressable latch.

Parts you’ll need:

• CD4099B addressable latch
• Arduino microcontroller (Any model will do)
• 16 LEDs

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