11. Input devices

Group assignment

Measure the analog levels and digital signals in an input device

Individual assignment

Measure something: add a sensor to a microcontroller board that you have designed and read it.

Research

To begin with, I don’t fully understand how to design my own board, but I have some understanding of what an input device is. I will review assignments from previous Fab Academy students to help with how to design my board/input device and test it.

After some review of the material, I chose to rework a temperature sensor board based on Neil’s design*(link).

Input Device: Read temperature

Components

  • Thermistor
  • ISP 2x3 Pin Header
  • ATtiny45
  • 10k Ohm Resistor (x4)
  • 1uF Capacitor
  • FTDI 6x1 Pin Header

Board Design

I’ll be designing the board in Eagle (9.3.2 Education).

Schematic

Schematic

Once that schematic was translated into a board, the connections didn’t work. I created another schematic with the proper connections:

Schematic

…and from that I created my board:

Board

…and then my worst nightmare happened: the Thermistor that I was able to find in the Eagle libraries did not produce pads on the board (see the route/trace connecting to nothing in the lower right corner, and compare to the drawing above). I believe these parts are for through-hole boards and not surface mount boards, thus the parts don’t produce pads on Eagle boards.

Board2

After numerous google searches and asking for support, I was unable to find a library with a usable thermistor.

Here are the libraries that I downloaded: - fab library - Eagle fab library - Thermistor library - …and another library that I found on GitHub that I wasn’t able to upload to Eagle.

I’m stuck and I’ve basically run out of time. I’ve found Eagle very frustrating to use, but at this point, it is the program that I’m familiar with.

I’ve encountered difficulties with finding the proper part within the Eagle libraries. Previously, I was able to find what I needed. No such luck this time.

Update

So, Blair Evans (Incite Focus) gave me the tip to use a resistor in place of a thermistor, since they have the same physical layout.

updated schematic