[IAEP] [support-gang] What Sensors and Where To Buy?

[James Cameron]

On Fri, Sep 21, 2012 at 03:38:12PM -0700, Kevin Mark wrote:
> This is a minor update because I was reading a post[1] on sparkfun. This kit
> shows a kit with single  examples of various types of sensors. This kit is too
> expensive but you can buy the individual parts separately at their site or
> elsewhere.
> [1] https://www.sparkfun.com/products/11283

Thanks.  Interesting.

Not every sensor works with an OLPC XO though, and the teaching of the
sensors themselves is more difficult with the highly integrated
sensors, since they don't provide a simple voltage as output.

Looking at SparkFun's DEV-11283 Sensor kit, I have the following
comments:

> HMC5883L - Triple-Axis Magnetometer Breakout Board -  An accurate,
> simple-to-use digital magnetometer with an I2C interface.

Can be connected to the OLPC XO USB socket via a microcontroller.

> ADXL335 - Triple-Axis Accelerometer Breakout Board - Senses
> acceleration along all three axes, with a range of up to ±3g. Fully
> analog interface.

Can be connected to the OLPC XO USB socket via a microcontroller.

> ITG-3200 - Triple-Axis Gyro Breakout Board - Senses angular velocity
> along three axes of rotation. Fully digital interface with a range
> of up to ±2000°/s.

Can be connected to the OLPC XO USB socket via a microcontroller.

> Large Piezo Vibration Sensor - With Mass - A flexible film able to
> sense for vibration, touch, shock, etc. When the film moves back and
> forth an AC wave is created, with a voltage of up to ±90.

Can be connected to the OLPC XO microphone input directly, with the
input configured for AC.  May require a series resistor, given the
maximum voltage of 90V.

> Reed Switch - Senses magnetic fields, makes for a great non-contact
> switch.

Can be connected to the OLPC XO microphone input directly, with the
input configured for DC with bias.

> 0.25" Magnet Square - Plays nicely with the reed switch. Embed the
> magnet into stuffed animals or inside a box to create a hidden
> actuator to the reed switch.

Is not connected.  Pity the stuffed animal.

> 0.5" Force Sensitive Resistor - A force sensing resistor with a 0.5"
> diameter sensing area. Great for sensing pressure (i.e. if it's
> being squeezed).

Can be connected to the OLPC XO microphone input directly, with the
input configured for DC with bias.

> PIR Motion Sensor - Easy-to-use motion detector with an analog
> interface. Power it with 5-12VDC, and you'll be alerted of any
> movement.

Can be connected to the OLPC XO microphone input and the USB socket
for power.

> Ultrasonic Rangefinder - Maxbotix LV-EZ1 - Distance sensor with both
> analog and RS-232 interfaces, providing sonar range information from
> 6 to 254 inches.

Can be connected to the OLPC XO microphone input, and the USB socket
for power.  May require a voltage divider, given the analog output of
10mV per inch, 2.55V maximum over 255 inches.

> HIH-4030 Humidity Sensor - A high precision humidity sensor with an
> analog output.

Can be connected to the OLPC XO microphone input and the USB socket
for power.  May require a voltage divider.

> IR Receiver Breakout Board - An analog interfaced IR receiver,
> sensitive to a wide range of IR waves. Great for 'listening' to TV
> remotes.

Can be connected to the OLPC XO microphone input and the USB socket
for power.  May require a voltage divider.

> Mini Photocell - The photocell will vary its resistance based on how
> much light it's exposed to. Will vary from 1kΩ in the light to 10kΩ
> in the dark.

Can be connected to the OLPC XO microphone input directly.

> Optical Detector/Phototransistor - An all-in-one infrared emitter
> and detector. Ideal for sensing black-to-white transitions or can be
> used to detect nearby objects.

Can be connected to the OLPC XO microphone input and the USB socket
for power, in a similar fashion to the LM35D on the Wiki.

> BMP085 Barometric Pressure Sensor - Low power, high precision
> barometric pressure sensor with I2C output.

Can be connected to the OLPC XO USB socket via a microcontroller.

> Flex Sensor - As the sensor is flexed, the resistance across the
> sensor increases. Useful for sensing motion or positioning

Can be connected to the OLPC XO microphone input directly.

> SoftPot - These are very thin variable potentiometers. By pressing
> on various positions along the strip, you vary the resistance.

Can be connected to the OLPC XO microphone input directly.

When I say above that a microcontroller is needed, this is because the
output of the sensor is not directly compatible with the OLPC XO, and
will require conversion.  The USB socket on the OLPC XO has the most
utility for this.

Other things to take into account are:

- the software for the microcontroller (Turtle Art plugins exist for
  at least Arduino and ExpEyes),

- the cost of the microcontroller,

- the increased complexity of setup; write the script, connect the
  microcontroller to the XO, connect the device to the
  microcontroller.

-- 
James Cameron
http://quozl.linux.org.au/