Archive for the Category » Phys Comp «

Sunday, November 18th, 2007 | Author:

Idle values:

  • x: 73-77
  • y: 84-88
  • z: 126-129


Roll Right 90d tilt values:

  • x: 34-36
  • y: 88-90
  • z: 84-86


Roll Left 90d tilt values:

  • x: 117 – 119
  • y: 85-87
  • z: 83-86


Pitch up 90 values:

  • x: 73 – 76
  • y: 44 – 47
  • z: 84 – 87


Pitch down 90d

  • x: 75 – 77
  • y: 126 – 128
  • z: 81 – 83


Palm motion towards self is the same as palm motion away from self. One way to differentiate this is to high visibility of finger tip when palm is pointing towards self.

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Thursday, November 15th, 2007 | Author:

Chapter One

The Design of Everyday Things by Don Norman

This book is a good descriptions of the principles of design. Norman starts off with some absurd product designs which do not account for human use. He then makes some detailed analyses of the usability of everyday products. He succinctly outlines principles of design such as conceptual models, natural mappings, affordances and feedback. I especially like his examples of bad design.

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Tuesday, November 13th, 2007 | Author:

So it turned out that my accelerometer was busted. When I swapped with the same model no overheating occurred. My guess is that during soldering I must have damaged the circuit board. Can it still be fixed/salvaged? Hard to say.

So now I’m working with a 2nd MMA7260Q. The values I’m getting are much more strange than with the 1st accelerometer. These are range of values when it is sitting idle.

Before activating SLP switch to HIGH

  • X: 16 – 97
  • Y: 16 – 97
  • Z: 24 – 99

After activating SLP switch to HIGH

  • X: 121 – 399
  • Y: 195 – 426
  • Z: 400 – 601

Adding Low Pass Filter

  • X: 143 – 684
  • Y: 159 – 686
  • Z: 319 – 703

These are values while just sitting still. Why? Another observation I don’t understand is why do the value fluctuations increase after adding the low pass filter?

Below are the circuit schematic that I used:


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Monday, November 12th, 2007 | Author:

So I’m working on the MMA7260Q 3-Axis Accelerometer and ran into several problems..

1. Overheating

I’m powering the 3.3V accelerometer from the 5V arduino, and using a 3.3V voltage regulator. In spite of this, the chip still starts getting very hot.

2. Signal Jitter

I was getting a lot of signal jitter even when the accelerometer was just sitting idle. I started to use a decoupling capacitor and low-pass filter.

Capacitors store up electricity while current is flowing into them, then release the energy when the incoming current is removed. Sometimes they are polarized, meaning current can only flow through them in a specific direction, and sometimes they are not. If a capacitor is polarized, it will be marked as such on the diagram. Don’t wire a polarized capacitor backwards; it might explode.

A basic low-pass filter consists of a resistor and a capacitor. If you’re dimming an LED, start with a 10µf capacitor and a 220-ohm resistor, and experiment with different values from there to see what works best.

If you find the readings from your analog inputs are inconsistent (for example, you see changes on one channel when the sensor on a different channel is the one sensing action), it helps to decouple your input circuit. Decoupling means smoothing out the dips and spikes going into the circuit from the rest of your microcontroller circuit. To do this, place a 0.1microfarad capacitor from voltage to ground as close to where the analog input connects to voltage.

Accelerometer Ranges for 1st Iteration

X: 114-123

Y: 139-150

Z: 195-206


2nd: add .1mF capacitor to accelerometer




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Wednesday, October 31st, 2007 | Author:


  • zigbee protocol
  • ASCII Based
  • AT Protocol
  • Command mode or Data mode


Set Command Mode: +++

Response: OK

Node Discover: ATND

Return ID: ATID


ATMY (Characters get sent out to serial port and do not screen display)

Response: 2200F0E3 (address)


Xbee site:

  • - download data sheet and product manual
  • - Xbee has analog and digital inputs
  • - microcontroller that is configurable but not programmable
  • - AT command set is in product manual



  • - Xbee breakout board
  • - Xbee to USB adapter – droids
  • - Xbee shield – breakout board
  • - serial to USB breakout board
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