Plus Shield

Introduction

Plus Shield helps lead out the 40 pins of Raspberry Pi 2 Module B or Raspberry Pi 1 Module B+ with screening print marks (BCM marks, see figure Plus Shield Pin Arrangement) at each pin. The shield integrates AD-DA chip and RTC chips, both of which use the I2C communication protocol and occupy no pins. For detailed materials of the chips, visit the WIKI section of our website www.sunfounder.com.

Schematic

Plus_shield_v1.6 schematic

Software Installation

Take the following procedures of installation step by step.

Step 1. Enable I2C and SPI

Run the command to open Raspberry Pi Software Configuration Tool (raspi-config)

sudo raspi-config

Enable I2C: Select Advanced Options =>I2C => <Yes> => <Ok> => <Yes>
Enable SPI: Select Advanced Options => SPI => <Yes> => <Ok> => <Yes> => <Ok> Select <Finish>. Close raspi-config.
If a message of rebooting appears, click <No>. Before reboot, we still need to complete some configurations.

Step 2. Add SPI, I2C, 1-Wire and RTC kernel module to the /etc/modules list

Open /etc/modules

sudo nano /etc/modules

Add the following contents at the end of the file (but if one or more such lines already exist in the file, you do not need to repeat them; just make sure the following lines are included).

snd-bcm2835
spi_bcm2708
spidev
i2c-dev
w1-gpio
w1-therm
rtc-ds1307

Save and exit.

Step 3. Enable I2C, SPI and 1-Wire hardware interfaces

Open /boot/config.txt

sudo nano /boot/config.txt

Add the following contents at the end of the file.

dtparam=spi=on
dtparam=i2c_arm=on
dtoverlay=w1-gpio

Save and exit.

Step 4. Create DS1307 (device creation) at boot

Open /etc/rc.local

sudo nano /etc/rc.local

Add before the line exit 0:

# For Raspberry Pi 1
echo ds1307 0x68 > /sys/class/i2c-adapter/i2c-0/new_device

# For Raspberry Pi 2
echo ds1307 0x68 > /sys/class/i2c-adapter/i2c-1/new_device

exit 0

Save and exit.

Step 5. Install related software packages

sudo apt-get update
sudo apt-get upgrade
sudo apt-get install git i2c-tools python-smbus

Git is a code management software that you can use to obtain or update the code we provide. Or you may learn to use Git and GitHub so you can manage and share your code conveniently.
Now you can reboot.

sudo reboot

Step 6. Download source code

Clone the source code from our GitHub page:

cd ~git clone https://github.com/sunfounder/SunFounder_PiPlus 

Step 7. Install SunFounder_PiPlus package to your Raspberry Pi

Run setup.py to install

cd SunFounder_PiPlus
sudo python setup.py install –c

Add –c at the end, so after the SunFounder_PiPlus package is installed, you can set the time for DS1307.Also you can make the setting anytime by running ds1307setup.py.

sudo python ds1307setup.py

Then follow the guide to complete the setting of ds1307 time.

Application

There are two chips on the Plus Shield: DS1307 and PCF8591.

DS1307

First, check whether the time of DS1307 is correct:

sudo hwclock –r

If it goes wrong, change directory to SunFounder_PiPlus/ and run ds1307setup.py to modify the time.

cd ~/SunFounder_PiPlus/
sudo python ds1307setup.py

Run the example:

cd ~/SunFounder_PiPlus/shield_example/
sudo python plus_ds1307.py

Then you can see the time printed on the screen. Open plus_ds1307.py with nano:

nano plus_ds1307.py

You can see the parameter of DS1307(clock) is HOUR12. You can restore the function get_split_datetime() to the 24-hour format.
You may check the application of the function under main() – comments after #.

'''
get_split_datetime(), get date, time seperatelyj
'''
#date, time = DT.get_split_datetime()
#print 'date:', date
#print 'time:', time
<pre>
Delete the mark # at the beginning of the three lines below and comment the part of '''DT.get_datetime()''', as shown below: 
<pre>
def main():
	while True:
		'''
		get_datetime() return the output of 'hwclock -r' 
		command
		'''
		#datetime = DT.get_datetime()
		#print datetime
		'''
		get_split_datetime(), get date, time seperatelyj
		'''
		date, time = DT.get_split_datetime()
		print 'date:', date
		print 'time:', time

Press Esc to exit. Type in the command wq. Save and exit.

Run plus_ds1307.py again

sudo python plus_ds1307.py

Then you can see the date and time printed separately on the screen.

PCF8591

PCF8591 is an AD-DA conversion chip that adopts I2C communication method. Its address is 0x27. Since a 3.3V is applied to the chip, when using the analog pins, please make sure the voltage is no larger than 3.3V.
Plug in an analog module (e.g. one of the modules in the SunFounder Sensor Kit for Raspberry Pi).
Run the example:

cd ~/SunFounder_PiPlus/shield_example/
sudo python plus_pcf8591.py

The values read of AIN0 and AIN3 will be printed on the screen, as well as the output value of AOUT.
Open plus_pcf8591.py with nano:

nano plus_pcf8591.py

In the setup() function, ADC = PCF8591() is to initialize the PCF8591 chip.
In the main() function, the function read_all() is to read all the four input analog values.
read(channel) is to read the analog value of a specific pin. Channel is the input pin among AIN0~AIN3 (can be defined in SunFounder_PiPlus.Shield), which can also be indicated by 0-3.
write(value) is to output the analog value which ranges from 0~255.
Now try to read a single analog value by read()!
Plug in a device that can output analog values. Modify the sketch and run:

sudo python plus_pcf8591.py