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Showing posts from March, 2012

The not so intuitive use of an IMU

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A recent project required acceleration measurements to study a person's gait. I thought this could be done easily with one of the many MEMS (MicroElectroMechanical Systems) devices available in the market under the name of IMU (Intertial Measurement Units) or just accelerometers.

I settled with the cheapest acceloremeter I found on eBay with an I2C interface to connect it to a Funnel IO powered by a rechargeable Lithium battery. Funnel IO (or FIO in short) is an Arduino-like board that includes a USB-powered battery charger plus an XBee module interface on board. It can be programmed wirelessly but this proved to be a real PITA to get it working (and even after that, it does not work reliably).

Once I got some code grabbed from Arduino forums to read my sensor (MMA7660FC from Freescale) I was a bit shocked with the results. My sensor was a 3-axis accelerometer and  I was expecting a measurement of X=Y=Z=0 on my first test with the sensor static. I was wrong. I should have read fi…

Wireless 3D printing

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Last week I had a "USB cable incident" with my Prusa (computer and printers are on different tables in my office). It was entirely my fault as I walked across the USB cable and I almost threw my printer to the floor. As a result, the ferrite torus I put in the USB cable to prevent EMI problems broke. Without it, I know prints may interrupt anytime due to interference.

While on eBay looking for a replacement, I realized that a Bluetooth module was costing less than $15 now. So I thought I could give it a chance to the idea of operating my printers wirelessly.   Later, I learned of an even cheaper module at $6.60, but this one is 3.3v only (which is ok if you are using this voltage for your Arduino, but I am using 5v).

A quick look at Sprinter firmware and Arduino Mega and RAMPS board specs revealed that Serial2 port using 16 (TX) and 17 (RX) pins was easily available on the ext4 connector of RAMPS board. And so was GND and +5V. Making it very easy to connect the Bluetooth mod…

Arduino RFID

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This time I am interested on a particular application of this technology: My university has moved to RFID picture IDs for students and I was curious about how difficult it was to read the cards from an Arduino board. Our system is using 13.56 MHz cards, so I ventured into eBay territory. Almost anyone can type "Arduino RFID" there to get plenty of cards that allow you to read (and write) RFID tags/cards.

For those of you living in a cave, RFID is a wireless technology that allows you to both power and interact wirelessly with a card or tag that contains a digital unique identifier that optionally may include some rewritable memory too. Tags or cards themselves do not have nor need a battery but they contain a microchip and a coil to gather energy from nearby readers. That means that the card and the reader need to be pretty close for this to work (that is why the technology is dubbed as NFC or Near Field Communication).

After buying one card and waiting the usual two weeks …