Net Objects

Wireless: Radio basics and Bluetooth Part 1

Physical layer:

radio: electromagnetic wave sent over air
putting electro-induction in one wire and listening on the other

frequency dependent
convert the changes into something meaningful (i.e. serial data)

FM:
frequency modulation
shifting (analog) wavelengths (if tuning into 88mhz - will shift between 87-89…)
changing timing
clearer signal
signal strength stays same
takes up more bandwidth

AM:
amplitude modulation
further distance
signal strength changes (especially at the distance - drops off)
same frequency
works at consistent

Digital over radio:
FSK: Frequency shift keying (takes a little longer)
ASK : Amplitude shift keying (degradation over range)
OOK: On Off Keying (don’t know diff between off and nothing)

line of site matters.
multi-path: signal is not direct line of site - came by bouncing off walls (lead paint, metal, galvanized tin, etc)
metal blocks radio: the metal absorbs the electricity - acting as an antennae
faraday cage - Enemy of the State style. http://en.wikipedia.org/wiki/Faraday_cage
- An external electrical field causes the charges to rearrange which cancels the field inside.

radio has no ground. so problems with interference are huge.

Bluetooth:
can handle media exchange, but basic ones aren’t built in: only serial sending (control info)
protocol designed at baud rate: 9600

AT command set: text way of sending commands to modems

http://www.makingthingstalk.com/chapter2/77/
(sparkfun just changed the radio, so the AT command set has changed since Making Things Talk)

always send in ASCII mode (so you don’t send raw data that messes up pairing and AT commands)