Table of Contents
Expander Shield Kit Tutorial
Product Description:
The Expander Shield Kit allows you to build a Digispark shield which connects a PCF8574P Remote 8-bit I/O expander IC to the Digispark development board. It communicates with the Digispark over the I2C bus and provides 8 more digital i/o pins that can be controlled by the Digispark.
This is an unassembled kit and requires basic soldering. This is designed for use with the Digispark development board, which is not included.
Parts:
| Part | Quantity | Identification |
|---|---|---|
| Expander Shield PCB | 1 | |
| 4.7K (4K7) Ohm 1/4W resistor 1% or 5% | 2 | Yellow - Violet - Red |
| 16 pin DIP socket | 1 | |
| PCF8574P IC | 1 | |
| 1×8 pin female 0.1“ pitch header | 1 | |
| 1x40pin male 0.1” pitch header | 9 pins worth | |
Resistor Values: For more information on how to identify the value of the resistors we recommend these sites: A nice simple resistor calculator: http://www.ealnet.com/m-eal/resistor/resistor.htm A comprehensive article on identification: http://www.diyaudioandvideo.com/Electronics/Color/
Soldering: If you are new to soldering we recommend the following tutorials: Soldering Basics (http://www.sparkfun.com/tutorials/106) and Soldering Crash Course from the folks at Sparkfun (http://www.sparkfun.com/tutorials/354). How to solder from the Curious Inventor: http://store.curiousinventor.com/guides/How_to_Solder
Adafruit has this excellent guide that starts with the tools needed and then shows detailed pictures, including some of the common problems that beginners experience (http://learn.adafruit.com/adafruit-guide-excellent-soldering)
We assume for these assembly instructions that you know the basics of thru-hole soldering. If you don't check out the links above, these boards are very easy to solder - we promise!
Assembly:
NOTE: If you have a “Model B” board you may need to cut the trace to the onboard LED before using any I2C devices - Find out how to tell which board you have and what to do here: modelbi2c
Empty kit bag (or if using a raw PCB, aquire parts) and verify contents. Note for Kickstarter Backers and Pre-orders: Headers are not included in each kit bag, but the entire order came with more than enough headers for all kits.
Solder resistors one at a time. Solder the leads and clip off the excess. Repeat for all resistors.
Insert the 16 pin DIP socket into the board matching the indention cut out on one end with the indention printed on the board.
Insert the 8 pin female header (on the top of the board) and solder each pin.
Cut a length of male headers 6 pins long and one 3 pins long. Insert into corresponding positions (on the bottom of the board) and solder each pin.
Tip: Inseting the headers into a breadboard and then placing the board on top can make this process easier.
Note: If you are using stackable headers, use them here instead of the standard male headers.
Insert the PCF8574P expander IC into the 16 pin DIP socket matching the indention cut out on one end with the indention on the socket.
Your expander shield is complete!
Programming:
The pin connections are as follows:
Digispark P0 → SDA
Digispark P2 → SCL
The I2C Address is 0x20 - this address can be changes with the on-board solder jumpers. Please refer to the schematic and datasheet for more info.
Please refer to the expander example included with the Digispark Arduino Addon.
