RoadTest: PiFace Digital
Author: mcb1
Creation date:
Evaluation Type: Independent Products
Did you receive all parts the manufacturer stated would be included in the package?: True
What other parts do you consider comparable to this product?: Pi Crust, ALaMode, RaspiRobot
What were the biggest problems encountered?: The software has been updated and the instruction not updated. Software distribution link is to an uncompressed, and not up to date distro.
Detailed Review:
The PiFace Digital is a useful add-on to the RaspberryPi.
It features 8 digital inputs, and 8 open collector outputs, as well as 2 relays.
The designers have added LEDs on the outputs, and pushbuttons on 4 of the inputs to aid the user.
The board neatly fits around the various connectors, but covers all the onboard connectors, unlike the PiCrust.
(image http://picru.st/ )
PiFace have gone to the trouble of fitting a rubber buffer that rests on the HDMI connector and shaped the board nicely to fit around the Ethernet, USB and composite video connectors.
It is well labelled, with jumper options to isolate the relays and back emf diodes, and the relays are rated at 250v at 10Amps, BUT the board is NOT designed for 230v.!
There is an option to change the boards address, but the mystery is how you connect more boards.
The one biggest grip I have is access to the remaining GPIO pins.
The connector is not pass through, and it is not duplicated or brought out anywhere else.
The user has two options.
1. Remove the existing connector and fit an offering from Adafruit (E14 code 2296136). This involves desoldering the existing connector, which probably means removing the relay.
2. Fit two single row headers onto the existing connector.
I elected to do the second method.
While a second PiFace can be connected, the pins are not in very deep for a reliable connection, so the use of longer headers would be advisable.
The other option could be a ribbon cable arrangement, however both methods have mounting/supporting issues.
Personally I would rather have it very slightly higher, to allow the board connectors to be used.
If the GPIO was brought to the diagonally opposite corner, it would allow a second board to be rotated 180 deg and fitted, and keep it all within the same footprint.
Application
My test application was to control two relays with a temperature sensor (DS18B20), with one relay coming on at low temperatures, and the other at higher.
There are setting for the ON and OFF temperatures of both relays (4 settings) so that a reasonable hysterisis is available.
I have done this with both Arduino and a Digispark with the results displayed on a I2C LCD.
I thought the RaspberryPi would allow a web page and the ability for the user to easily control the 4 temperature settings.
I found the necessary information to access the temperature sensor here :-
http://learn.adafruit.com/adafruits-raspberry-pi-lesson-11-ds18b20-temperature-sensing
While they use a breakout board its the same pins.
This is a useful resource :-
http://elinux.org/Rpi_Low-level_peripherals
The "Getting Started" documentation explains what distribution to use, and how to talk to the Piface in python, but the software has been updated to name the relays 1-8, (so don't try to specify relay 0).
The only minor issue is the distribution suggested is not compressed, and rather than 550MB is a bit over 2GB.
Its also not the latest, so when you do a an update, you're waiting for a while while it downloads and replaces the various modules.
The more Linux savvy people might go "why didn't you use xyz and do abc", and they could be right, but I'm not in that league, so I followed the instructions.
Python is new to me so its taking longer than I wanted, as well as looking at some alternative methods including PiWiring.
As a consequence the software is not finished ....yet.
I'll post the result when I have completed it.
The Piface is a very capable addition, and allows users to connect it to the real world.
Mark
edit
The attached review is from The Shed magazine, a NZ Hobby type magazine that features 'How to' articles on Woodwork, Metalwork, Home renovation and inc Electronics.
