Ultrasound related information

An Introduction to Ultrasound
What is a decibel
Texas Instrument Application Note
Atmospheric Sound Absorption Calculator

SP-elektroniikka ultrasound receiver and transmitter (page 77)
Typical ultrasound receiver and transmitter

Operaatiovahvistin
Basics of an operational amplifier

Wikipedia Farad


Atmel AVR microcontrollers:

AVR-freaks. Everything about ATmel AVR microcontrollers (specs, tools, code samples, links...)
Atmel's AVR web site Software (Atmel studio, AVR GNU compiler etc.) and datasheets.

IC manufacturers:

Maxim IC / Dallas semiconductor
Texas instruments
National semiconductor
Philips semiconductor
Atmel
ST microelectronics

IC distributors:

Farnell   preferred source for component orders
Elfa

IC shops:

SP-elektroniikka   preferred source for component orders
Suomen huoltopalvelu (Oulussa)
Bebek
PartCo
El-kama
Elektrolinna