Circuit notes

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Some miscellaneous analog & digital circuit notes:

Analog filter

Series-RC.png

The frequency at which the filter attenuates to half it's original power is:

f = 1 / ( 2 x pi x R x C )
Where:
f = frequency in Hz
R = resistance in Ohms
C = capacitance in Farads

According to Atmel - a 10 kohm resistor and a 100 nF capacitor produces a filter with a 1 kHz 'crossover' frequency?!? Evil Mad scientist labs suggest a 33 kohm resistor and a 22 uF capacitor. I've been using 1.8kohm and a 10nF capacitor.

To make a high-pass filter, swap the resistor and capacitor.


Variable Resistor

VariableResistorArduino.png

On my Arduino, I see numbers in the range ~90 to ~1020 returned from analogRead(0) depending on the position of the knob. It's very non-linear though.


Switch

Arduino switch.png

The resistor is needed to avoid shorting out the Arduino pin if it's programmed as an output by mistake.


LED

Arduino LED.png

Minimal ATmega Circuit

Minimal ATmega.png

ATmega (As used on Arduino boards)

Atmega168PinMap2.png

Audio without DAC

Arduino audio.png

WaveShield DAC datasheet

MCP4921/4922 datasheet

Hooking up a Relay

Relay arduino.png



Wikiid Pages relating to Arduino (edit)
Arduino
Command line Arduino
Startup code for Arduino
Low level functions for Arduino
Putting data in flash on the Arduino
External resources for Arduino
Board schematics for Arduino
Misc notes: Circuit notes, Music notes, Stepper motors