< for ATtiny45, the small AVR microcontroller
in the inventory. Other ATtiny's and ATMega's (including the Mega328P used in Arduino) are similar.
XMEGAs have more capabilities.
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###Microcontrollers.
As circuit elements. Programming will be discussed later.
Pins: Supply (2.7-5.5V), ground, reset. Other pins available for input and output. Configured by programming to be input or output.
#### Input.
- Digital inputs (using VCC=5V): Low for 0 - ~2.3 V. High for 2.3 - 5 V.
- Individual pins can be configured to have an input pullup resistor.
This is used, for example, to make a simple button input circuit.
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- Analog to Digital converter. (ADC) "Analog" input. Uses digital process to infer analog voltage.
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- Built-in analog amplifier. Attiny45 has a 20X differential amplifier.
#### Output.
- Digital output. Low (0 V), high (Supply voltage, e.g. 5V), tri-state (floating, with high input impedance).
- what can the ucontroller drive?
- Things with high input impedance: FETs, Piezoelectric transducers, other microcontroller inputs.
- To some extent, things with low imput impedance: maximum current is 40mA per I/O pin. Enough to (over)drive LEDs.
- One way to get "Analog" out: Pulse width modulation (PWM)
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