This is a repository for a talk I gave at the Go Meetup on April 14, 2014 at Google Zürich.

Slides

The slides were presented with the Go present tool. You can find all the necessary files in the pres subfolder. The code examples in the slides all use the content of the file pres/serialport to decide on which serial port to talk to the I2C bus master. Change it to match your system, do not put a newline in the file.

The talk concluded with a little gag, the Googly Eyed Gopher, which is described towards the end of this file.

Hardware

The talk was supported by a number of code examples which communicated with hardware on a breadboard. On the breadboard I wired 3 devices onto an I2C bus. The I2C bus lines were pulled up to VCC by 5kOhm resistors. The voltage of the power supply was 3.3V.

The I2C bus was driven by a Bus Pirate. The Bus Pirate contains a USB-to-serial converter, thus ultimately the software interface to the Bus Pirate is a serial port, albeit a relatively virtual one.

The circuit on the breadboard consisted of the following. All chips are relatively easy to obtain from electronics distributors. Schematics will follow.

EEPROM

A 24C02 2kbit EEPROM with all address lines (A2:A0) pulled to GND. Thus, the EEPROM responds to the 7 bit address 0x50 a.k.a. the 8 bit address pair 0xa0/0xa1.

I/O Expander

An MCP23008 8-bit I/O expander. All address lines (A2:A0) were pulled to GND. Thus, the I/O expanders responds to the 7 bit address 0x20, a.k.a. the 8 bit address pair 0x40/0x41. To Pin 0, a resistor and an LED were connected in series in positive logic: a high level on Pin 0 turned on the LED.

A/D Converter

A PCF8591P 4 channel 8 bit A/D and 1 channel 8 bit D/A converter. All address lines (A2:A0) were pulled to GND, making the chip respond to the 7 bit address 0x48, a.k.a. the 8 bit address pair 0x90/0x91. The reference voltage was VCC=3.3V. To A/D channel 0, the middle tap of a potentiometer was connected. The other taps of the potentiometer were at VCC and GND, respectively.

The Googly Eyed Gopher

The subfodler gg contains the source code for the Googly Eyed Gopher. The Go program in gg.go continously reads A/D samples from A/D channel 0 of the A/D converter on the breadboard. The Go program also serves a static index page, index.html and the 2 images for the Gopher. The index page is peppered with some Javascript that opens a websocket to the Go server. On this connection, the Go server continously sends fresh A/D samples which the JS side translates into rotations of the Gopher's pupils.