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<title>Electronics intro:  microcontrollers.  </title>

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## Microcontrollers.

  [Datasheet](https://datasheet.octopart.com/ATTINY45-20SU-Atmel-datasheet-41301906.pdf) 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.

  ![picture](../images/t45_pinout.png)

  #### 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.

  ![picture](../images/input_pullup.jpg)

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  - Analog to Digital converter.  (ADC)  "Analog" input.  Uses digital process to infer analog voltage.

![picture](../images/pot_input.jpg)

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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)

![picture](../images/input_output.jpg)

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