Week 11

Input Devices
(Apr 13)

Assignment:

measure something: add a sensor to a microcontroller board that you have designed and read it

Design a board, add a sensor and read it

• Note from lecture

  - beware of bit timing
  - pyroelectric measures changes of temperature. thermal radiation from your body. activity detector
  - sonar : ultrasonic transducers is just a pair of microphone and a loud speaker 
  designed to run above audio frequencies
  it only work if you get a reflection. e.g. if you tilt a surface it doesnt work. 
  the procesor has timer and counter. trigger and wait for echo.
  how far you can see depends on how good is the reflector
  - magnetic field : mostly used for proximity to magnet field. there's a sign so. 
  at the finest resolution you can measure earth's magnetic field meaning it can be used 
  also for orientation. produces analog output. convert analog-digital
  - web interface : node.js, a web page can not talk directly to usb ports cos security issues. 
  we use web socket, local server 	
  local server : javascript program talks to node. node is javascripts in a browser 
  but running out of the browser
  npm is packages for node. there's npm serialport 
  - temperature :2 standard kind : NTC and RTD
  NTC : goes to lower temp, more sensitive
  RTD : goes to higher temp, less sensitive
  both of them are not linear. neeed calibration.. fix resistor / variable resistor ??? 
  use a bridge to measure small changs, small signal
  - framing ? low byte / high byte ??
  - light : phototransistor : bipolar transistor 
  - Bit banging is a technique for serial 
  communications using software instead of dedicated hardware. 
  Software directly sets and samples the state of pins on the microcontroller, and is responsible 
  for all parameters of the signal: timing, levels, synchronization, etc.
  - I2C / SPI protocol...
  - identify objects : sample from MOMA : vinyl-cut rasonator.
  Each object has a vinyl-cut coil with a capacitor, 
  each ring has different freqency. the resonate frequency of the ringing way of distinguish objects
  
  			

1. Intro : Capacitive sensing

What is Capacitive sensing ? Here's the meaning from Wikipedia

capacitive sensing is a technology, based on capacitive coupling, that can detect and measure anything that is conductive or has a dielectric different from air.

Many types of sensors use capacitive sensing, including sensors to detect and measure proximity, position or displacement, humidity, fluid level, and acceleration.

What is step response ?

Main reference projects: touchpad, multitouch

Similar projects : Sabina | Luca's push button | Satsha Kit

2. Temperature

1. This is the sensor I have and its datasheet

2. I soldered it on pins to test the circuit

3. The result is not so varied so I tried with different resistence

4.

5.In the end I adopted easier way, using a ready-made temperature sensor. image source

Which is anyhow very jittery... as it can be seen from this visualization I made with vvvv

6. So I added also a capacitive surface in order to give a on/off toggle when to use the temperature input

7. Then I hook everything up with my modified Satshakit in which I add also the RF transmitter

Download files :
the crossfix file (dxf) for laser cut
Modified Satshajib (png) for laser cut
Arduino program (ino) for temperature & capacitive read

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